AQ_GEN_PLNG_20220404_SIP_RH-SIP_AppE2a

Appendix E-2a

Regional Haze Modeling for Southwestern VISTAS II
Regional Haze Analysis Project 2011el and 2028el
CAMx Benchmarking Report

Benchmark Runs #1 and #2

August 17, 2020

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Regional Haze Modeling for Southeastern
VISTAS II Regional Haze Analysis Project
2011el and 2028el CAMx Benchmarking
Report

Task 6 Benchmark Report #1
Covering Benchmark Runs #1 and #2

Prepared for:
Southeastern States Air Resource
Managers, Inc.
205 Corporate Center Dr., Suite D
Stockbridge, GA 30281-7383

Under Contract No. V-2018-03-01

Prepared by:
Alpine Geophysics, LLC
387 Pollard Mine Road
Burnsville, NC 28714

and

Eastern Research Group, Inc.
1600 Perimeter Park Dr., Suite 200
Morrisville, NC 27560

Final - August 17, 2020

Alpine Project Number: TS-527
ERG Project Number: 4133.00.006

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 ii

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CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 iii
Contents
Page
1.0 EPA 2011 AND 2028 BASE CASE CONFIRMATION .................................................1
2.0 DIFFERENCES BETWEEN EPA AND VISTAS SIMULATIONS ...............................2
3.0 CONFIRMATION METHODOLOGY ............................................................................3
4.0 CAMX 6.32 2011EL COMPARISON .............................................................................4
4.1 Ozone ....................................................................................................................4
4.2 PM2.5 ...................................................................................................................27
4.3 Sulfate .................................................................................................................50
4.4 Nitrate .................................................................................................................73
4.5 Organic Carbon (OC) ..........................................................................................96
5.0 CAMX 6.32 2028EL COMPARISON .........................................................................119
5.1 Ozone ................................................................................................................119
5.2 PM2.5 .................................................................................................................142
5.3 Sulfate ...............................................................................................................165
5.4 Nitrate ...............................................................................................................188
5.5 Organic Carbon (OC) ........................................................................................211
6.0 CONCLUSION .............................................................................................................234

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 iv
TABLES
Table 4-1. Comparison of 2011el CAMx 6.32 Simulation Ozone Concentrations (ppb) Run
on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum Positive
and Maximum Negative Differences are Shown. ................................................................5
Table 4-2. Comparison of 2011el CAMx 6.32 Simulation PM2.5 Concentrations (µg/m3) Run
on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum Positive
and Maximum Negative Differences are Shown. ..............................................................28
Table 4-3. Comparison of 2011el CAMx 6.32 Simulation Sulfate Concentrations (µg/m3)
Run on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum
Positive and Maximum Negative Differences are Shown. ................................................51
Table 4-4. Comparison of 2011el CAMx 6.32 Simulation Nitrate Concentrations (µg/m3)
Run on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum
Positive and Maximum Negative Differences are Shown. ................................................74
Table 4-5. Comparison of 2011el CAMx 6.32 Simulation Organic Carbon Concentrations
(µg/m3) Run on VISTAS and EPA Computer Systems. Hours with the Top 10
Maximum Positive and Maximum Negative Differences are Shown. ..............................97
Table 5-1. Comparison of 2028el CAMx 6.32 Simulation Ozone Concentrations (ppb) Run
on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum Positive
and Maximum Negative Differences are Shown. ............................................................120
Table 5-2. Comparison of 2028el CAMx 6.32 Simulation PM2.5 Concentrations (µg/m3) Run
on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum Positive
and Maximum Negative Differences are Shown. ............................................................143
Table 5-3. Comparison of 2028el CAMx 6.32 Simulation Sulfate Concentrations (µg/m3)
Run on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum
Positive and Maximum Negative Differences are Shown. ..............................................166
Table 5-4. Comparison of 2028el CAMx 6.32 Simulation Nitrate Concentrations (µg/m3)
Run on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum
Positive and Maximum Negative Differences are Shown. ..............................................189
Table 5-5. Comparison of 2028el CAMx 6.32 Simulation Organic Carbon Concentrations
(µg/m3) Run on VISTAS and EPA Computer Systems. Hours with the Top 10
Maximum Positive and Maximum Negative Differences are Shown. ............................212

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 v
FIGURES
Figure 4-1: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Maximum Positive Difference) ..........................................................6
Figure 4-2: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Second Highest Positive Difference) ..................................................7
Figure 4-3: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Third Highest Positive Difference).....................................................8
Figure 4-4: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Fourth Highest Positive Difference) ...................................................9
Figure 4-5: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Fifth Highest Positive Difference) ....................................................10
Figure 4-6: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Sixth Highest Positive Difference) ...................................................11
Figure 4-7: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Seventh Highest Positive Difference) ...............................................12
Figure 4-8: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Eighth Highest Positive Difference) .................................................13
Figure 4-9: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Ninth Highest Positive Difference) ..................................................14
Figure 4-10: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Tenth Highest Positive Difference) ..................................................15
Figure 4-11: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Maximum Negative Difference) .......................................................16
Figure 4-12: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Second Highest Negative Difference) ..............................................17
Figure 4-13: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Third Highest Negative Difference) .................................................18
Figure 4-14: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Fourth Highest Negative Difference) ...............................................19
Figure 4-15: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Fifth Highest Negative Difference) ..................................................20
Figure 4-16: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Sixth Highest Negative Difference) .................................................21
Figure 4-17: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Seventh Highest Negative Difference) .............................................22
Figure 4-18: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Eighth Highest Negative Difference) ...............................................23

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 vi
Figure 4-19: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Ninth Highest Negative Difference) .................................................24
Figure 4-20: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx
6.32 2011el Simulations (Tenth Highest Negative Difference) .....................................25
Figure 4-21: Scatterplot Comparing 24-hour Average Predicted Ozone Concentrations
(ppb) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2011el
Simulations Performed by EPA and VISTAS (Alpine). ...............................................26
Figure 4-22: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Maximum Positive Difference) ........................................................29
Figure 4-23: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Second Highest Positive Difference) ................................................30
Figure 4-24: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Third Highest Positive Difference)...................................................31
Figure 4-25: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Fourth Highest Positive Difference) .................................................32
Figure 4-26: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Fifth Highest Positive Difference) ....................................................33
Figure 4-27: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Sixth Highest Positive Difference) ...................................................34
Figure 4-28: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Seventh Highest Positive Difference) ...............................................35
Figure 4-29: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Eighth Highest Positive Difference) .................................................36
Figure 4-30: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Ninth Highest Positive Difference) ..................................................37
Figure 4-31: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Tenth Highest Positive Difference) ..................................................38
Figure 4-32: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Maximum Negative Difference) .......................................................39
Figure 4-33: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Second Highest Negative Difference) ..............................................40
Figure 4-34: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Third Highest Negative Difference) .................................................41
Figure 4-35: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Fourth Highest Negative Difference) ...............................................42
Figure 4-36: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Fifth Highest Negative Difference) ..................................................43

CAMx 2011el and 2018el Benchmarking Report – revised draft

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Figure 4-37: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Sixth Highest Negative Difference) .................................................44
Figure 4-38: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Seventh Highest Negative Difference) .............................................45
Figure 4-39: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Eighth Highest Negative Difference) ...............................................46
Figure 4-40: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Ninth Highest Negative Difference) .................................................47
Figure 4-41: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2011el Simulations (Tenth Highest Negative Difference).................................................48
Figure 4-42: Scatterplot Comparing 24-hour Average Predicted PM2.5 Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2011el
Simulations Performed by EPA and VISTAS (Alpine). ....................................................49
Figure 4-43: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Maximum Positive Difference) ................................................52
Figure 4-44: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Second Highest Positive Difference) ........................................53
Figure 4-45: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Third Highest Positive Difference)...........................................54
Figure 4-46: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fourth Highest Positive Difference) .........................................55
Figure 4-47: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fifth Highest Positive Difference) ............................................56
Figure 4-48: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Sixth Highest Positive Difference) ...........................................57
Figure 4-49: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Seventh Highest Positive Difference).......................................58
Figure 4-50: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Eighth Highest Positive Difference) .........................................59
Figure 4-51: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Ninth Highest Positive Difference) ..........................................60
Figure 4-52: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Tenth Highest Positive Difference) ..........................................61
Figure 4-53: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Maximum Negative Difference) ...............................................62
Figure 4-54: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Second Highest Negative Difference) ......................................63

CAMx 2011el and 2018el Benchmarking Report – revised draft

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Figure 4-55: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Third Highest Negative Difference) .........................................64
Figure 4-56: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fourth Highest Negative Difference) .......................................65
Figure 4-57: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fifth Highest Negative Difference) ..........................................66
Figure 4-58: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Sixth Highest Negative Difference) .........................................67
Figure 4-59: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Seventh Highest Negative Difference) .....................................68
Figure 4-60: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Eighth Highest Negative Difference) .......................................69
Figure 4-61: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Ninth Highest Negative Difference) .........................................70
Figure 4-62: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Tenth Highest Negative Difference) ........................71
Figure 4-63: Scatterplot Comparing 24-hour Average Predicted Sulfate Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2011el
Simulations Performed by EPA and VISTAS (Alpine). ....................................................72
Figure 4-64: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Maximum Positive Difference) ................................................75
Figure 4-65: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Second Highest Positive Difference) ........................................76
Figure 4-66: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Third Highest Positive Difference)...........................................77
Figure 4-67: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fourth Highest Positive Difference) .........................................78
Figure 4-68: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fifth Highest Positive Difference) ............................................79
Figure 4-69: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Sixth Highest Positive Difference) ...........................................80
Figure 4-70: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Seventh Highest Positive Difference).......................................81
Figure 4-71: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Eighth Highest Positive Difference) .........................................82
Figure 4-72: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Ninth Highest Positive Difference) ..........................................83

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Figure 4-73: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Tenth Highest Positive Difference) ..........................................84
Figure 4-74: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Maximum Negative Difference) ...............................................85
Figure 4-75: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Second Highest Negative Difference) ......................................86
Figure 4-76: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Third Highest Negative Difference) .........................................87
Figure 4-77: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fourth Highest Negative Difference) .......................................88
Figure 4-78: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fifth Highest Negative Difference) ..........................................89
Figure 4-79: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Sixth Highest Negative Difference) .........................................90
Figure 4-80: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Seventh Highest Negative Difference) .....................................91
Figure 4-81: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Eighth Highest Negative Difference) .......................................92
Figure 4-82: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Ninth Highest Negative Difference) .........................................93
Figure 4-83: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Tenth Highest Negative Difference) ........................94
Figure 4-84: Scatterplot Comparing 24-hour Average Predicted Nitrate Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2011el
Simulations Performed by EPA and VISTAS (Alpine). ....................................................95
Figure 4-85: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Maximum Positive Difference) ....................................98
Figure 4-86: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Second Highest Positive Difference) ............................99
Figure 4-87: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Third Highest Positive Difference) ............................100
Figure 4-88: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Fourth Highest Positive Difference) ...........................101
Figure 4-89: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Fifth Highest Positive Difference) ..............................102
Figure 4-90: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Sixth Highest Positive Difference) .............................103

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 x
Figure 4-91: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Seventh Highest Positive Difference) ........................104
Figure 4-92: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Eighth Highest Positive Difference) ...........................105
Figure 4-93: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Ninth Highest Positive Difference) ............................106
Figure 4-94: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Tenth Highest Positive Difference) ............................107
Figure 4-95: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Maximum Negative Difference) .................................108
Figure 4-96: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Second Highest Negative Difference) ........................109
Figure 4-97: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Third Highest Negative Difference) ...........................110
Figure 4-98: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Fourth Highest Negative Difference) .........................111
Figure 4-99: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Fifth Highest Negative Difference) ............................112
Figure 4-100: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Sixth Highest Negative Difference) ...........................113
Figure 4-101: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Seventh Highest Negative Difference) .......................114
Figure 4-102: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Eighth Highest Negative Difference) .........................115
Figure 4-103: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Ninth Highest Negative Difference) ...........................116
Figure 4-104: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Tenth Highest Negative Difference) ..........................117
Figure 4-105: Scatterplot Comparing 24-hour Average Predicted Organic Carbon
Concentrations (µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx
6.32 2011el Simulations Performed by EPA and VISTAS (Alpine). ..............................118
Figure 5-1: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Maximum Positive Difference) ......................................................121
Figure 5-2: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Second Highest Positive Difference) ..............................................122
Figure 5-3: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Third Highest Positive Difference).................................................123

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Figure 5-4: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Fourth Highest Positive Difference) ...............................................124
Figure 5-4: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Fourth Highest Positive Difference) ...............................................125
Figure 5-6: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Sixth Highest Positive Difference) .................................................126
Figure 5-7: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Seventh Highest Positive Difference) .............................................127
Figure 5-8: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Eighth Highest Positive Difference) ...............................................128
Figure 5-9: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Ninth Highest Positive Difference) ................................................129
Figure 5-10: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Tenth Highest Positive Difference) ................................................130
Figure 5-11: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Maximum Negative Difference) .....................................................131
Figure 5-12: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Second Highest Negative Difference) ............................................132
Figure 5-13: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Third Highest Negative Difference) ...............................................133
Figure 5-14: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Fourth Highest Negative Difference) .............................................134
Figure 5-15: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Fifth Highest Negative Difference) ................................................135
Figure 5-16: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Sixth Highest Negative Difference) ...............................................136
Figure 5-17: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Seventh Highest Negative Difference) ...........................................137
Figure 5-18: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Eighth Highest Negative Difference) .............................................138
Figure 5-19: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Ninth Highest Negative Difference) ...............................................139
Figure 5-20: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Tenth Highest Negative Difference)...............................................140
Figure 5-21: Scatterplot Comparing 24-hour Average Predicted Ozone Concentrations (ppb)
for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2028el Simulations
Performed by EPA and VISTAS (Alpine). ......................................................................141

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Figure 5-22: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Maximum Positive Difference) ......................................................144
Figure 5-23: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Second Highest Positive Difference) ..............................................145
Figure 5-24: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Third Highest Positive Difference).................................................146
Figure 5-25: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Fourth Highest Positive Difference) ...............................................147
Figure 5-26: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Fifth Highest Positive Difference) ..................................................148
Figure 5-27: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Sixth Highest Positive Difference) .................................................149
Figure 5-28: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Seventh Highest Positive Difference) .............................................150
Figure 5-29: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Eighth Highest Positive Difference) ...............................................151
Figure 5-30: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Ninth Highest Positive Difference) ................................................152
Figure 5-31: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Tenth Highest Positive Difference) ................................................153
Figure 5-32: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Maximum Negative Difference) .....................................................154
Figure 5-33: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Second Highest Negative Difference) ............................................155
Figure 5-34: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Third Highest Negative Difference) ...............................................156
Figure 5-35: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Fourth Highest Negative Difference) .............................................157
Figure 5-36: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Fifth Highest Negative Difference) ................................................158
Figure 5-37: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Sixth Highest Negative Difference) ...............................................159
Figure 5-38: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Seventh Highest Negative Difference) ...........................................160
Figure 5-39: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Eighth Highest Negative Difference) .............................................161
Figure 5-40: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Ninth Highest Negative Difference) ...............................................162

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August 17, 2020 xiii
Figure 5-41: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx 6.32
2028el Simulations (Tenth Highest Negative Difference)...............................................163
Figure 5-42: Scatterplot Comparing 24-hour Average Predicted PM2.5 Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2028el
Simulations Performed by EPA and VISTAS (Alpine). ..................................................164
Figure 5-43: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Maximum Positive Difference) ..............................................167
Figure 5-44: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Second Highest Positive Difference) ......................................168
Figure 5-45: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Third Highest Positive Difference).........................................169
Figure 5-46: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fourth Highest Positive Difference) .......................................170
Figure 5-47: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fifth Highest Positive Difference) ..........................................171
Figure 5-48: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Sixth Highest Positive Difference) .........................................172
Figure 5-49: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Seventh Highest Positive Difference).....................................173
Figure 5-50: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Eighth Highest Positive Difference) .......................................174
Figure 5-51: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Ninth Highest Positive Difference) ........................................175
Figure 5-52: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Tenth Highest Positive Difference) ........................................176
Figure 5-53: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Maximum Negative Difference) .............................................177
Figure 5-54: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Second Highest Negative Difference) ....................................178
Figure 5-55: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Third Highest Negative Difference) .......................................179
Figure 5-56: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fourth Highest Negative Difference) .....................................180
Figure 5-57: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fifth Highest Negative Difference) ........................................181
Figure 5-58: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Sixth Highest Negative Difference) .......................................182

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Figure 5-59: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Seventh Highest Negative Difference) ...................................183
Figure 5-60: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Eighth Highest Negative Difference) .....................................184
Figure 5-61: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Ninth Highest Negative Difference) .......................................185
Figure 5-62: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Tenth Highest Negative Difference) ......................186
Figure 5-63: Scatterplot Comparing 24-hour Average Predicted Sulfate Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2028el
Simulations Performed by EPA and VISTAS (Alpine). ..................................................187
Figure 5-64: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Maximum Positive Difference) ..............................................190
Figure 5-65: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Second Highest Positive Difference) ......................................191
Figure 5-66: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Third Highest Positive Difference).........................................192
Figure 5-67: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fourth Highest Positive Difference) .......................................193
Figure 5-68: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fifth Highest Positive Difference) ..........................................194
Figure 5-69: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Sixth Highest Positive Difference) .........................................195
Figure 5-70: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Seventh Highest Positive Difference).....................................196
Figure 5-71: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Eighth Highest Positive Difference) .......................................197
Figure 5-72: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Ninth Highest Positive Difference) ........................................198
Figure 5-73: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Tenth Highest Positive Difference) ........................................199
Figure 5-74: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Maximum Negative Difference) .............................................200
Figure 5-75: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Second Highest Negative Difference) ....................................201
Figure 5-76: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Third Highest Negative Difference) .......................................202

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August 17, 2020 xv
Figure 5-77: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fourth Highest Negative Difference) .....................................203
Figure 5-78: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fifth Highest Negative Difference) ........................................204
Figure 5-79: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Sixth Highest Negative Difference) .......................................205
Figure 5-80: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Seventh Highest Negative Difference) ...................................206
Figure 5-81: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Eighth Highest Negative Difference) .....................................207
Figure 5-82: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Ninth Highest Negative Difference) .......................................208
Figure 5-83: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Tenth Highest Negative Difference) ......................209
Figure 5-84: Scatterplot Comparing 24-hour Average Predicted Nitrate Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2028el
Simulations Performed by EPA and VISTAS (Alpine). ..................................................210
Figure 5-85: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Maximum Positive Difference) ..................................213
Figure 5-86: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Second Highest Positive Difference) ..........................214
Figure 5-87: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Third Highest Positive Difference) ............................215
Figure 5-88: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Fourth Highest Positive Difference) ...........................216
Figure 5-89: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Fifth Highest Positive Difference) ..............................217
Figure 5-90: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Sixth Highest Positive Difference) .............................218
Figure 5-91: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Seventh Highest Positive Difference) ........................219
Figure 5-92: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Eighth Highest Positive Difference) ...........................220
Figure 5-93: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Ninth Highest Positive Difference) ............................221
Figure 5-94: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Tenth Highest Positive Difference) ............................222

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Figure 5-95: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Maximum Negative Difference) .................................223
Figure 5-96: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Second Highest Negative Difference) ........................224
Figure 5-97: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Third Highest Negative Difference) ...........................225
Figure 5-98: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Fourth Highest Negative Difference) .........................226
Figure 5-99: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Fifth Highest Negative Difference) ............................227
Figure 5-100: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Sixth Highest Negative Difference) ...........................228
Figure 5-101: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Seventh Highest Negative Difference) .......................229
Figure 5-102: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Eighth Highest Negative Difference) .........................230
Figure 5-103: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Ninth Highest Negative Difference) ...........................231
Figure 5-104: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and
EPA CAMx 6.32 2028el Simulations (Tenth Highest Negative Difference) .............232
Figure 5-105: Scatterplot Comparing 24-hour Average Predicted Organic Carbon Concentrations (µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx
6.32 2028el Simulations Performed by EPA and VISTAS (Alpine). ..............................233

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1.0 EPA 2011 AND 2028 BASE CASE CONFIRMATION
Alpine has executed two confirmation runs, one for the 2011el base year and one for the
2028el base case, to confirm the contract team’s ability to replicate EPA’s results and to ensure
that the EPA data, models, and scripts operated in a consistent manner as EPA’s procedure.
The data for this analysis are paired in space and time, meaning that each plot represents
a comparison of the two simulations at the same monitor on the same day. Although there is
some variability between the two runs, the runs are not expected to be exactly the same due to
numerical differences that arises from the different computing architectures used for the U.S.
EPA and Alpine simulations. The numerics in photochemical grid models are very complex and
it is typical to get slightly different model concentrations based on the version of the computer
and compilers. When comparing simulations, it is critical to isolate the changes in concentrations
to the changes in the model inputs, and not on the computing details (i.e., compiler version,
computer architecture, parallelization options). This is especially problematic when looking at
particulate matter, since the particulate treatments have multiple pathways, and small
concentration differences can lead to different pathways through the code and different
concentrations.
Sources of the difference can come from the options used in CAMx compilation, the
version of the compiler, the compiler vendor, and how the model calculation is split onto
different processors (parallelization).

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August 17, 2020 2
2.0 DIFFERENCES BETWEEN EPA AND VISTAS SIMULATIONS
EPA ran the 2011v6.3el platform on EPA’s supercomputer with the model configured to
use four (4) processor nodes with 16 processors per node. The use of multiple processor nodes
with multiple processors per node is efficient on the EPA supercomputer due to the low latency
interconnect between the nodes. On more typical computer clusters with the nodes
interconnected with Ethernet, like the Alpine cluster and most likely the State and stakeholder
clusters, the latency between nodes is sufficiently high that it is inefficient to spread processing
between nodes. Our experience with the EPA platform has shown that on an Ethernet connected
cluster with 12 Intel XEON processors per node and hyperthreading enabled it is most efficient
to use a single node configured with 10 Message Passing Interface (MPI) instances, each with
two OpenMP threads.
EPA used the Intel FORTRAN compiler. Alpine, and the CAMx developers, use the
Portland Group (PGI) FORTRAN compiler. The PGI compiler has been the standard compiler
for CAMx applications for many years and it’s anticipated this compiler will be more widely
used by the States and stakeholders. The version of CAMx 6.32 EPA distributed with the 2011el
platform will be recompiled on the Alpine computer system and used for the confirmation.
EPA ran the model in two time segments. The first segment, typically used only for PM
applications, runs from December 22, 2010 through April 30, 2011. The second segment runs
from April 21, 2011 through December 31, 2011. The VISTAS confirmation run used the same
two segments. December 22-31, 2010 and the April portion of the second segment are spin-ups
and are not analyzed due to overlap with the first segment.

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August 17, 2020 3
3.0 CONFIRMATION METHODOLOGY
The comparison of simulations on the Alpine computer cluster and the EPA computer are
based on hourly differences in ozone, particulate matter less than 2.5 microns in aerodynamic
diameter (PM2.5), organic carbon (OC), Particulate Nitrate, and Particulate Sulfate. The metrics
for comparison are the absolute difference (Equation 1) and percent difference (Equation 2)
defined as:
(Equation 1) �𝐶𝐶𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣−𝐶𝐶𝑒𝑒𝑒𝑒𝑣𝑣�

(Equation 2) �𝐶𝐶𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣−𝐶𝐶𝑒𝑒𝑒𝑒𝑣𝑣��𝐶𝐶𝑒𝑒𝑒𝑒𝑣𝑣�

where: Cepa is the concentration at each grid cell hour for the EPA simulation and
Cvistas is the concentration at each grid cell hour for the simulation on the Alpine
computers.
The results are presented for the hours with the largest difference between the EPA and
VISTAS simulations. A table presents the hours with the top 10 positive and negative absolute
differences. Spatial maps are presented for the hours with the top 10 highest positive and
negative differences. To provide context for the differences, the concentration maps are also
presented for each of the hours of high difference. On each spatial plot the maximum positive
and negative values, along with the grid cell in which these occur, are presented at the top of the
graphic. The coordinates refer to the row and columns of the cell referenced to the cell
coordinates on the bottom (column) and left (row) of the graphic.
Hourly animations have also been prepared and are available on the VISTAS II project
ftp site. Where appropriate, this report also reports and interprets on the animations.

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August 17, 2020 4
4.0 CAMX 6.32 2011EL COMPARISON
This section presents comparisons of the 2011el simulations using CAMx 6.32 performed
on the Alpine and EPA computer systems.
4.1 Ozone
Ozone results for the top 10 positive and negative hours are presented in tabular format in
Table 4-1. The maximum positive difference is 3.13 ppb falling to 2.01 ppb for the 10th high. The
maximum negative difference is -2.65 ppb falling to -1.79 for the 10th high. The highest
differences are occurring on relatively low ozone hours with concentrations ranging from 30 ppb
to 51 ppb for the EPA simulation. The maximum positive and negative percent differences are
both 7.4%.

The top ten positive impact hours are presented in Figures 4-1 through 4-10 and the top
ten negative impact hours are presented in Figures 4-11 through 4-20. The locations of the
impacts are very localized and have seemingly no spatial pattern. On the hours with the
maximum impacts the overwhelming number of grid cells have impacts less than 0.01 ppb.

Scatterplots of the daily average ozone concentrations in local standard time at the
IMPROVE monitors are presented in Figure 4-21. The EPA results are plotted on the x-axis and
the VISTAS (Alpine) results are plotted on the y-axis. The data has a near perfect degree of
correlation with a line of best fit with a slope of 1.0000, an intercept of 0.0001 ppb and an R2 of
1.0000.

Examination of the animations show that the differences appear suddenly over very
limited areas, then the areas of difference disperse and travel downwind and become less than the
0.01 ppb plotting threshold typically within six (6) hours of forming.

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August 17, 2020 5
Table 4-1. Comparison of 2011el CAMx 6.32 Simulation Ozone Concentrations (ppb) Run
on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum Positive and
Maximum Negative Differences are Shown.
Year Month Day Hour VISTAS
Conc.
EPA
Conc.
Difference
(ppb)
Percent
Difference Column Row
Maximum Positive
2011 7 14 22 45.15 42.02 3.13 7.4% 292 77
2011 8 18 23 53.60 50.83 2.77 5.5% 286 152
2011 8 19 0 45.25 42.64 2.61 6.1% 286 152
2011 7 6 23 48.49 45.90 2.59 5.6% 197 156
2011 8 30 14 32.28 29.96 2.33 7.8% 110 217
2011 8 7 16 37.14 34.94 2.20 6.3% 257 103
2011 8 27 12 34.34 32.22 2.13 6.6% 295 143
2011 8 23 22 44.30 42.22 2.08 4.9% 323 47
2011 8 8 23 39.44 37.43 2.01 5.4% 217 184
2011 7 7 0 43.63 41.62 2.01 4.8% 197 156
Maximum Negative
2011 8 16 0 33.32 35.96 -2.65 -7.4% 251 134
2011 7 15 21 48.71 51.16 -2.44 -4.8% 224 159
2011 8 15 23 36.83 39.27 -2.44 -6.2% 251 134
2011 6 18 22 33.70 36.07 -2.37 -6.6% 196 187
2011 6 26 22 34.14 36.40 -2.26 -6.2% 206 183
2011 7 7 16 39.38 41.34 -1.97 -4.8% 216 180
2011 8 11 18 35.28 37.21 -1.92 -5.2% 332 28
2011 3 30 10 42.23 44.13 -1.90 -4.3% 117 19
2011 7 16 19 48.28 50.08 -1.80 -3.6% 196 189
2011 6 18 23 32.77 34.57 -1.79 -5.2% 196 187

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Maximum Positive Difference: July 14 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-1: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Maximum Positive Difference)

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August 17, 2020 7
Second Highest Positive Difference: August 18 at 2300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-2: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Second Highest Positive Difference)

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August 17, 2020 8
Third Highest Positive Difference: August 19 at 0000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-3: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Third Highest Positive Difference)

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August 17, 2020 9
Fourth Highest Positive Difference: July 6 at 2300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-4: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Fourth Highest Positive Difference)

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Fifth Highest Positive Difference: August 30 at 1400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-5: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Fifth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

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Sixth Highest Positive Difference: August 7 at 1600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-6: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Sixth Highest Positive Difference)

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August 17, 2020 12
Seventh Highest Positive Difference: August 27 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-7: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Seventh Highest Positive Difference)

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August 17, 2020 13
Eighth Highest Positive Difference: August 23 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-8: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Eighth Highest Positive Difference)

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August 17, 2020 14
Ninth Highest Positive Difference: August 8 at 2300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-9: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Ninth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

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Tenth Highest Positive Difference: July 7 at 0000 hours
VISTAS Simulation
Difference (VISTAS-EPA)

Figure 4-10: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Tenth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 16
Maximum Negative Difference: August 16 at 0000 hours
VISTAS Simulation
Difference (VISTAS-EPA)

Figure 4-11: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Maximum Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 17
Second Highest Negative Difference: July 15 at 2100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-12: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Second Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 18
Third Highest Negative Difference: August 15 at 2300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-13: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Third Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 19
Fourth Highest Negative Difference: June 18 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-14: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Fourth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 20
Fifth Highest Negative Difference: June 26 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-15: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Fifth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 21
Sixth Highest Negative Difference: July 7 at 1600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-16: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Sixth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 22
Seventh Highest Negative Difference: August 11 at 1800 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-17: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Seventh Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 23
Eighth Highest Negative Difference: March 30 at 1000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-18: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Eighth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 24
Ninth Highest Negative Difference: July 16 at 1900 hours
VISTAS Simulation
Difference (VISTAS-EPA)

Figure 4-19: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Ninth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 25
Tenth Highest Negative Difference: June 18 at 2300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-20: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2011el Simulations (Tenth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 26
Figure 4-21: Scatterplot Comparing 24-hour Average Predicted Ozone Concentrations
(ppb) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2011el Simulations
Performed by EPA and VISTAS (Alpine).

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 27
4.2 PM2.5
PM2.5 results for the top 10 positive and negative hours are presented in tabular format in
Table 4-2. The maximum positive difference is 6.73 µg/m3 falling to 2.21 µg/m3 for the 10th
high. The maximum negative difference is -5.41 µg/m3 falling to -1.97 µg/m3 for the 10th high.
The maximum positive percent difference from these days is 44.5% and negative percent
difference of -31.7%, both on low PM2.5 concentration days.

The top 10 positive impact hours are presented in Figures 4-22 through 4-31 and the top
10 negative impact hours are presented in Figures 4-32 through 4-41. The locations of the
impacts are again localized and tending to occur in Canada near the relatively high concentration
entering the domain through the northern boundary. Comparison with the Nitrate results in
Section 4.4 shows that on many days the principal difference in the PM2.5 concentrations is a
result of the differences in the Nitrate predictions.

Scatterplots of the daily average PM2.5 concentrations in local standard time at the
IMPROVE monitors are presented in Figure 4-42. The EPA results are plotted on the x-axis and
the VISTAS (Alpine) results are plotted on the y-axis. The data has a perfect degree of
correlation with a line of best fit with a slope of 1.0000, an intercept of 0.0000 ppb and an R2 of
1.0000.

Examination of the animations shows that the majority of the differences are occurring in
Canada and the Northern U.S. with the differences occurring in the areas of relatively high
PM2.5. We speculate that the differences are primarily from the difference in the Particulate
Nitrate and most likely from different pathways being taken in the ISOROPIA algorithm.

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 28
Table 4-2. Comparison of 2011el CAMx 6.32 Simulation PM2.5 Concentrations (µg/m3)
Run on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum Positive
and Maximum Negative Differences are Shown.
Year Month Day Hour VISTAS
Conc.
EPA
Conc.
Difference
(µg/m3)
Percent
Difference Column Row
Maximum Positive
2011 1 3 4 34.86 28.13 6.73 23.93% 156 236
2011 1 3 5 32.54 26.77 5.77 21.56% 156 236
2011 1 3 6 34.49 29.16 5.33 18.28% 156 235
2011 1 27 7 14.19 9.82 4.37 44.52% 349 244
2011 1 3 3 31.52 28.34 3.17 11.20% 156 236
2011 1 27 11 11.67 8.91 2.76 30.91% 349 243
2011 1 27 6 11.37 8.71 2.66 30.59% 343 244
2011 1 14 9 14.03 11.54 2.49 21.60% 164 222
2011 1 27 4 11.82 9.56 2.26 23.63% 343 244
2011 1 3 21 21.51 19.29 2.21 11.47% 164 236
Maximum Negative
2011 1 14 6 20.84 26.26 -5.41 -20.62% 120 243
2011 1 27 8 8.56 12.22 -3.67 -30.01% 350 243
2011 1 15 9 14.60 17.96 -3.36 -18.70% 126 220
2011 1 27 11 8.58 11.77 -3.19 -27.10% 342 245
2011 1 27 12 6.20 9.08 -2.88 -31.69% 342 243
2011 1 27 5 7.89 10.74 -2.85 -26.53% 342 244
2011 1 3 10 38.42 40.87 -2.45 -5.99% 155 235
2011 1 14 2 27.61 29.94 -2.32 -7.76% 134 242
2011 1 3 4 28.64 30.77 -2.13 -6.93% 157 237
2011 1 3 6 27.75 29.72 -1.97 -6.61% 159 234

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 29
Maximum Positive Difference: January 3 at 400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-22: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Maximum Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 30
Second Highest Positive Difference: January 3 at 500 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-23: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Second Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 31
Third Highest Positive Difference: January 3 at 600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-24: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Third Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 32
Fourth Highest Positive Difference: January 27 at 700 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-25: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fourth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 33
Fifth Highest Positive Difference: January 3 at 300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-26: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fifth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 34
Sixth Highest Positive Difference: January 27 at 1100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-27: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Sixth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 35
Seventh Highest Positive Difference: January 27 at 600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-28: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Seventh Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 36
Eighth Highest Positive Difference: January 14 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-29: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Eighth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 37
Ninth Highest Positive Difference: January 27 at 400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-30: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Ninth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 38
Tenth Highest Positive Difference: January 3 at 2100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-31: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Tenth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 39
Maximum Negative Difference: January 14 at 600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-32: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Maximum Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 40
Second Highest Negative Difference: January 27 at 800 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-33: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Second Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 41
Third Highest Negative Difference: January 15 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-34: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Third Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 42
Fourth Highest Negative Difference: January 27 at 1100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-35: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fourth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 43
Fifth Highest Negative Difference: January 27 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-36: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fifth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 44
Sixth Highest Negative Difference: January 27 at 500 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-37: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Sixth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 45
Seventh Highest Negative Difference: January 3 at 1000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-38: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Seventh Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 46
Eighth Highest Negative Difference: January 14 at 200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-39: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Eighth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 47
Ninth Highest Negative Difference: January 3 at 400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-40: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Ninth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 48
Tenth Highest Negative Difference: January 3 at 600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-41: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Tenth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 49

Figure 4-42: Scatterplot Comparing 24-hour Average Predicted PM2.5 Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2011el
Simulations Performed by EPA and VISTAS (Alpine).

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 50
4.3 Sulfate
Sulfate results for the top 10 positive and negative hours are presented in tabular format
in Table 4-3. The maximum positive difference is 0.31 µg/m3 falling to 0.19 µg/m3 for the 10th
high. The maximum negative difference is -0.40 µg/m3 falling to -0.14 µg/m3 for the 10th high.
The maximum positive percent difference from these days is 15.09% and negative percent
difference of -18.5%.

The top 10 positive impact hours are presented in Figures 4-43 through 4-52 and the top
10 negative impact hours are presented in Figures 4-53 through 4-62. The locations of the
impacts are considerably more localized than the nitrate differences, and are not occurring in any
systematic location, but are tending to occur in the colder months. The area of the differences
does not appear to be correlated with areas of high sulfate concentrations.

Scatterplots of the daily average sulfate concentrations in local standard time at the
IMPROVE monitors are presented in Figure 4-63. The EPA results are plotted on the x-axis and
the VISTAS (Alpine) results are plotted on the y-axis. The data has a perfect degree of
correlation with a line of best fit with a slope of 1.0000, an intercept of 0.0000 ppb and an R2 of
1.0000.

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 51
Table 4-3. Comparison of 2011el CAMx 6.32 Simulation Sulfate Concentrations (µg/m3)
Run on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum Positive
and Maximum Negative Differences are Shown.
Year Month Day Hour VISTAS
Conc.
EPA
Conc.
Difference
(µg/m3)
Percent
Difference Column Row
Maximum Positive
2011 12 31 16 14.98 14.67 0.31 2.12% 247 47
2011 11 29 15 4.91 4.60 0.31 6.74% 206 155
2011 1 10 3 2.20 1.91 0.29 15.09% 259 174
2011 12 31 15 14.06 13.78 0.28 2.06% 247 47
2011 12 14 22 6.46 6.18 0.28 4.54% 282 175
2011 4 9 9 6.40 6.14 0.26 4.21% 156 210
2011 4 8 2 7.66 7.41 0.25 3.31% 172 229
2011 11 29 16 4.44 4.22 0.23 5.36% 206 153
2011 4 9 10 6.46 6.23 0.22 3.57% 156 209
2011 4 9 8 6.19 6.00 0.19 3.19% 156 211
Maximum Negative
2011 12 6 0 5.65 6.05 -0.40 -6.55% 364 164
2011 12 14 22 5.28 5.63 -0.35 -6.22% 282 173
2011 12 6 1 5.48 5.77 -0.30 -5.13% 364 164
2011 2 6 17 3.72 3.95 -0.23 -5.79% 211 140
2011 5 28 7 2.39 2.61 -0.22 -8.39% 336 186
2011 2 6 16 3.11 3.29 -0.17 -5.29% 211 141
2011 5 14 7 0.64 0.79 -0.15 -18.53% 354 236
2011 12 18 11 3.06 3.21 -0.14 -4.51% 282 115
2011 12 29 16 4.24 4.38 -0.14 -3.28% 209 194
2011 12 30 11 2.82 2.95 -0.14 -4.68% 313 178

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 52
Maximum Positive Difference: December 31 at 1600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-43: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Maximum Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 53
Second Highest Positive Difference: November 29 at 1500 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-44: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Second Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 54
Third Highest Positive Difference: January 10 at 300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-45: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Third Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 55
Fourth Highest Positive Difference: December 31 at 1500 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-46: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fourth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 56
Fifth Highest Positive Difference: December 14 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-47: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fifth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 57
Sixth Highest Positive Difference: April 9 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-48: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Sixth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 58
Seventh Highest Positive Difference: April 8 at 200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-49: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Seventh Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 59
Eighth Highest Positive Difference: November 29 at 1600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-50: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Eighth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 60
Ninth Highest Positive Difference: April 9 at 1000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-51: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Ninth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 61
Tenth Highest Positive Difference: April 9 at 800 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-52: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Tenth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 62
Maximum Negative Difference: December 6 at 0000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-53: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Maximum Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 63
Second Highest Negative Difference: December 14 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-54: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Second Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 64
Third Highest Negative Difference: December 6 at 100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-55: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Third Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 65
Fourth Highest Negative Difference: February 6 at 1700 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-56: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fourth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 66
Fifth Highest Negative Difference: May 28 at 700 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-57: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fifth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 67
Sixth Highest Negative Difference: February 6 at 1600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-58: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Sixth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 68
Seventh Highest Negative Difference: May 14 at 700 hours
VISTAS Simulation
Difference (VISTAS-EPA)

Figure 4-59: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Seventh Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 69
Eighth Highest Negative Difference: December 18 at 1100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-60: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Eighth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 70
Ninth Highest Negative Difference: December 29 at 1600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-61: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Ninth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 71
Tenth Highest Negative Difference: December 30 at 1100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-62: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Tenth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 72

Figure 4-63: Scatterplot Comparing 24-hour Average Predicted Sulfate Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2011el
Simulations Performed by EPA and VISTAS (Alpine).

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 73
4.4 Nitrate
Nitrate results for the top 10 positive and negative hours are presented in tabular format
in Table 4-4. The maximum positive difference is 5.34 µg/m3 falling to 1.93 µg/m3 for the 10th
high. The maximum negative difference is -4.20 µg/m3 falling to -1.65 µg/m3 for the 10th high.
The maximum positive percent difference from these days is 110.0% and negative percent
difference of -54.5%, both on low Nitrate concentration days.

The top 10 positive impact hours are presented in Figures 4-64 through 4-73 and the top
10 negative impact hours are presented in Figures 4-74 through 4-83. As was discussed in
Section 4.2 for the PM2.5 concentrations, the differences are tending to occur in January along the
northern border in Canada.

Scatterplots of the daily average nitrate concentrations in local standard time at the
IMPROVE monitors are presented in Figure 4-84. The EPA results are plotted on the x-axis and
the VISTAS (Alpine) results are plotted on the y-axis. The data has a perfect degree of
correlation with a line of best fit with a slope of 1.0000, an intercept of 0.0000 ppb and an R2 of
1.0000.

Examination of the animations shows that the majority of the differences are occurring in
Canada and the Northern U.S. with the differences occurring in the areas of relatively high
PM2.5. We speculate that the differences are primarily from the difference in the Particulate
Nitrate and most likely from different pathways being taken in the ISOROPIA algorithm.

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 74
Table 4-4. Comparison of 2011el CAMx 6.32 Simulation Nitrate Concentrations (µg/m3)
Run on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum Positive
and Maximum Negative Differences are Shown.
Year Month Day Hour VISTAS
Conc.
EPA
Conc.
Difference
(µg/m3)
Percent
Difference Column Row
Maximum Positive
2011 1 3 4 24.70 19.36 5.34 27.60% 156 236
2011 1 3 5 22.87 18.32 4.55 24.84% 156 236
2011 1 27 7 8.33 3.97 4.36 110.03% 349 244
2011 1 3 6 23.13 18.99 4.15 21.84% 156 235
2011 1 27 11 6.60 3.95 2.65 66.94% 349 243
2011 1 3 3 21.99 19.49 2.50 12.85% 156 236
2011 1 27 6 5.72 3.22 2.50 77.54% 343 244
2011 1 27 4 8.79 6.61 2.18 33.08% 344 245
2011 5 19 13 6.83 4.90 1.94 39.59% 314 168
2011 1 14 9 8.78 6.84 1.93 28.24% 164 222
Maximum Negative
2011 1 14 6 14.35 18.55 -4.20 -22.62% 120 243
2011 1 27 8 2.99 6.64 -3.64 -54.92% 350 243
2011 1 27 11 3.82 6.97 -3.15 -45.21% 342 245
2011 1 27 12 2.25 4.96 -2.70 -54.54% 342 243
2011 1 27 5 2.53 5.17 -2.64 -51.13% 342 244
2011 1 15 9 9.50 12.11 -2.60 -21.51% 126 220
2011 1 3 10 25.95 27.85 -1.90 -6.83% 155 235
2011 1 27 9 4.37 6.21 -1.84 -29.60% 342 244
2011 1 14 2 19.31 21.10 -1.79 -8.50% 134 242
2011 1 3 4 19.76 21.41 -1.65 -7.72% 157 237

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 75
Maximum Positive Difference: January 3 at 400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-64: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Maximum Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 76
Second Highest Positive Difference: January 3 at 500 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-65: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Second Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 77
Third Highest Positive Difference: January 27 at 700 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-66: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Third Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 78
Fourth Highest Positive Difference: January 3 at 600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-67: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fourth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 79
Fifth Highest Positive Difference: January 27 at 1100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-68: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fifth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 80
Sixth Highest Positive Difference: January 3 at 300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-69: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Sixth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 81
Seventh Highest Positive Difference: January 27 at 600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-70: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Seventh Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 82
Eighth Highest Positive Difference: January 27 at 400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-71: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Eighth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 83
Ninth Highest Positive Difference: May 19 at 1300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-72: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Ninth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 84
Tenth Highest Positive Difference: January 14 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-73: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Tenth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 85
Maximum Negative Difference: January 14 at 600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-74: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Maximum Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 86
Second Highest Negative Difference: January 27 at 800 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-75: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Second Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 87
Third Highest Negative Difference: January 27 at 1100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-76: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Third Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 88
Fourth Highest Negative Difference: January 27 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-77: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fourth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 89
Fifth Highest Negative Difference: January 27 at 500 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-78: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Fifth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 90
Sixth Highest Negative Difference: January 15 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-79: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Sixth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 91
Seventh Highest Negative Difference: January 3 at 1000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-80: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Seventh Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 92
Eighth Highest Negative Difference: January 27 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-81: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Eighth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 93
Ninth Highest Negative Difference: January 14 at 200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-82: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Ninth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 94
Tenth Highest Negative Difference: January 3 at 400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-83: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2011el Simulations (Tenth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 95

Figure 4-84: Scatterplot Comparing 24-hour Average Predicted Nitrate Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2011el
Simulations Performed by EPA and VISTAS (Alpine).

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 96
4.5 Organic Carbon (OC)
Organic Carbon (OC) results for the top 10 positive and negative hours are presented in
tabular format in Table 4-5. The maximum positive difference is 0.18 µg/m3 falling to 0.09
µg/m3 for the 10th high. The maximum negative difference is -0.33 µg/m3 falling to -0.08 µg/m3
for the 10th high. The maximum positive percent difference from these days is 1.28% and
negative percent difference of -2.89%.

The top 10 positive impact hours are presented in Figures 4-85 through 4-94 and the top
10 negative impact hours are presented in Figures 4-95 through 4-104. The locations of the
impacts are extremely localized.

Scatterplots of the daily average OC concentrations in local standard time at the
IMPROVE monitors are presented in Figure 4-105. The EPA results are plotted on the x-axis and
the VISTAS (Alpine) results are plotted on the y-axis. The data has a perfect degree of
correlation with a line of best fit with a slope of 1.0000, an intercept of 0.0000 ppb and an R2 of
1.0000.

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 97
Table 4-5. Comparison of 2011el CAMx 6.32 Simulation Organic Carbon Concentrations
(µg/m3) Run on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum
Positive and Maximum Negative Differences are Shown.
Year Month Day Hour VISTAS
Conc.
EPA
Conc.
Difference
(µg/m3)
Percent
Difference Column Row
Maximum Positive
2011 6 26 12 17.32 17.13 0.18 1.08% 288 74
2011 5 20 12 11.46 11.32 0.14 1.23% 286 84
2011 8 26 12 10.82 10.69 0.14 1.28% 295 57
2011 5 20 13 10.89 10.77 0.12 1.16% 286 84
2011 12 15 17 25.91 25.80 0.12 0.45% 143 115
2011 7 14 22 5.30 5.19 0.11 2.03% 292 77
2011 6 26 13 12.40 12.31 0.10 0.79% 288 74
2011 7 26 12 10.30 10.21 0.09 0.93% 236 95
2011 8 26 13 7.69 7.60 0.09 1.23% 295 57
2011 8 23 22 7.38 7.29 0.09 1.28% 323 47
Maximum Negative
2011 12 20 9 10.97 11.30 -0.33 -2.89% 313 89
2011 12 20 8 11.31 11.59 -0.28 -2.39% 313 89
2011 5 21 0 8.28 8.39 -0.11 -1.37% 331 95
2011 12 20 10 11.20 11.31 -0.11 -0.96% 313 89
2011 2 14 23 18.47 18.58 -0.11 -0.57% 271 69
2011 2 14 22 16.07 16.17 -0.10 -0.65% 271 69
2011 8 4 14 13.21 13.31 -0.10 -0.75% 213 89
2011 7 19 12 7.28 7.37 -0.09 -1.22% 253 100
2011 8 1 0 8.21 8.29 -0.08 -1.01% 261 70
2011 7 15 13 5.29 5.38 -0.08 -1.56% 314 98

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 98
Maximum Positive Difference: June 26 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-85: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Maximum Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 99
Second Highest Positive Difference: May 20 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-86: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Second Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 100
Third Highest Positive Difference: August 26 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-87: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Third Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 101
Fourth Highest Positive Difference: May 20 at 1300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-88: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Fourth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 102
Fifth Highest Positive Difference: December 15 at 1700 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-89: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Fifth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 103
Sixth Highest Positive Difference: July 14 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-90: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Sixth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 104
Seventh Highest Positive Difference: June 26 at 1300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-91: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Seventh Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 105
Eighth Highest Positive Difference: July 26 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-92: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Eighth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 106
Ninth Highest Positive Difference: August 26 at 1300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-93: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Ninth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 107
Tenth Highest Positive Difference: August 23 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-94: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Tenth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 108
Maximum Negative Difference: December 20 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-95: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Maximum Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 109
Second Highest Negative Difference: December 20 at 800 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-96: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Second Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 110
Third Highest Negative Difference: May 21 at 0000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-97: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Third Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 111
Fourth Highest Negative Difference: December 20 at 1000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-98: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Fourth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 112
Fifth Highest Negative Difference: February 14 at 2300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-99: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2011el Simulations (Fifth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 113
Sixth Highest Negative Difference: February 14 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-100: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and
EPA CAMx 6.32 2011el Simulations (Sixth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 114
Seventh Highest Negative Difference: August 4 at 1400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-101: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and
EPA CAMx 6.32 2011el Simulations (Seventh Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 115
Eighth Highest Negative Difference: July 19 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-102: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and
EPA CAMx 6.32 2011el Simulations (Eighth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 116
Ninth Highest Negative Difference: August 1 at 0000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-103: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and
EPA CAMx 6.32 2011el Simulations (Ninth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 117
Tenth Highest Negative Difference: July 15 at 1300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 4-104: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and
EPA CAMx 6.32 2011el Simulations (Tenth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 118

Figure 4-105: Scatterplot Comparing 24-hour Average Predicted Organic Carbon
Concentrations (µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32
2011el Simulations Performed by EPA and VISTAS (Alpine).

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 119
5.0 CAMX 6.32 2028EL COMPARISON
This section presents comparisons of the 2028el simulations using CAMx 6.32 performed
on the Alpine and EPA computer systems.
5.1 Ozone
Ozone results for the top 10 positive and negative hours are presented in tabular format in
Table 5-1. The maximum positive difference is 2.24 ppb falling to 1.74 ppb for the 10th high. The
maximum negative difference is -2.25 ppb falling to -1.60 ppb for the 10th high. The highest
differences are occurring on relatively low ozone hours with concentrations ranging from 30 ppb
to 50 ppb for the EPA simulation. The maximum positive percent difference is 7.8% and the
maximum negative percent difference is -6.6%

The top ten positive impact hours are presented in Figures 5-1 through 5-10 and the top
ten negative impact hours are presented in Figures 5-11 through 5-20. The locations of the
impacts are very localized. On the hours with the maximum impacts the overwhelming number
of grid cells have impacts less than 0.01 ppb.

Scatterplots of the daily average ozone concentrations in local standard time at the
IMPROVE monitors are presented in Figure 5-21. The EPA results are plotted on the x-axis and
the VISTAS (Alpine) results are plotted on the y-axis. The data has a perfect degree of
correlation with a line of best fit with a slope of 1.0000, an intercept of 0.0000 ppb and an R2 of
1.0000.

The hours of the maximum differences, and the spatial patterns on those hours, are very
similar between the 2011el (Section 4.1) and 2028el. This is not surprising given that the
simulations differ only in the anthropogenic emissions inventories.

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 120
Table 5-1. Comparison of 2028el CAMx 6.32 Simulation Ozone Concentrations (ppb) Run
on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum Positive and
Maximum Negative Differences are Shown.
Year Month Day Hour VISTAS
Conc.
EPA
Conc.
Difference
(ppb)
Percent
Difference Column Row
Maximum Positive
2011 7 6 23 42.43 40.19 2.24 5.58% 197 156
2011 8 18 23 44.64 42.43 2.21 5.21% 286 152
2011 7 14 22 31.20 29.06 2.13 7.34% 292 77
2011 8 30 14 28.50 26.43 2.06 7.81% 110 217
2011 8 27 12 29.93 28.01 1.92 6.85% 295 143
2011 9 11 23 52.26 50.35 1.91 3.79% 167 218
2011 8 19 0 38.39 36.52 1.87 5.12% 286 152
2011 8 8 23 35.67 33.85 1.82 5.39% 217 184
2011 8 7 16 30.17 28.38 1.80 6.33% 257 103
2011 7 7 0 38.27 36.52 1.74 4.78% 197 156
Maximum Negative
2011 8 16 0 27.88 30.14 -2.25 -7.47% 251 134
2011 6 18 22 30.88 33.06 -2.18 -6.59% 196 187
2011 8 15 23 30.96 33.06 -2.10 -6.34% 251 134
2011 7 15 21 38.77 40.69 -1.92 -4.73% 224 159
2011 3 30 10 42.39 44.30 -1.91 -4.30% 117 19
2011 6 26 22 27.84 29.67 -1.83 -6.17% 206 183
2011 7 7 16 35.85 37.67 -1.82 -4.84% 216 180
2011 8 11 18 31.40 33.11 -1.72 -5.19% 332 28
2011 6 18 23 30.11 31.76 -1.65 -5.19% 196 187
2011 7 16 19 43.39 45.00 -1.60 -3.57% 196 189

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 121
Maximum Positive Difference: July 6 at 2300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-1: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Maximum Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 122
Second Highest Positive Difference: August 18 at 2300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-2: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Second Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 123
Third Highest Positive Difference: July 14 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-3: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Third Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 124
Fourth Highest Positive Difference: August 30 at 1400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-4: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Fourth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 125
Fifth Highest Positive Difference: August 27 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-5: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Fourth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 126
Sixth Highest Positive Difference: September 11 at 2300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-6: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Sixth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 127
Seventh Highest Positive Difference: August 19 at 0000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-7: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Seventh Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 128
Eighth Highest Positive Difference: August 8 at 2300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-8: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Eighth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 129
Ninth Highest Positive Difference: August 7 at 1600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-9: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Ninth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 130
Tenth Highest Positive Difference: July 7 at 0000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-10: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Tenth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 131
Maximum Negative Difference: August 16 at 0000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-11: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Maximum Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 132
Second Highest Negative Difference: June 18 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-12: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Second Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 133
Third Highest Negative Difference: August 15 at 2300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-13: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Third Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 134
Fourth Highest Negative Difference: July 15 at 2100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-14: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Fourth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 135
Fifth Highest Negative Difference: March 30 at 1000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-15: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Fifth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 136
Sixth Highest Negative Difference: June 26 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-16: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Sixth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 137
Seventh Highest Negative Difference: July 7 at 1600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-17: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Seventh Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 138
Eighth Highest Negative Difference: August 11 at 1800 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-18: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Eighth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 139
Ninth Highest Negative Difference: June 18 at 2300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-19: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Ninth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 140
Tenth Highest Negative Difference: July 16 at 1900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-20: Comparison of Ozone Concentrations (ppb) for VISTAS and EPA CAMx 6.32
2028el Simulations (Tenth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 141

Figure 5-21: Scatterplot Comparing 24-hour Average Predicted Ozone Concentrations
(ppb) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2028el Simulations
Performed by EPA and VISTAS (Alpine).

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 142
5.2 PM2.5
PM2.5 results for the top 10 positive and negative hours are presented in tabular format in
Table 5-2. The maximum positive difference is 5.15 µg/m3 falling to 2.84 µg/m3 for the 10th
high. The maximum negative difference is -4.61 µg/m3 falling to -2.45 µg/m3 for the 10th high.
The maximum positive percent difference from these days is 48.4% and negative percent
difference of -32.9%, both on low PM2.5 concentration days.

The top 10 positive impact hours are presented in Figures 5-22 through 5-31 and the top
10 negative impact hours are presented in Figures 5-32 through 5-41. The locations of the
impacts are again localized and tending to occur in Canada near the relatively high concentration
entering the domain through the northern boundary. Comparison with the nitrate results in
Section 5.4 shows that on many days the principal difference in the PM2.5 concentrations is a
result of the differences in the nitrate predictions.

Scatterplots of the daily average PM2.5 concentrations in local standard time at the
IMPROVE monitors are presented in Figure 5-42. The EPA results are plotted on the x-axis and
the VISTAS (Alpine) results are plotted on the y-axis. The data has a perfect degree of
correlation with a line of best fit with a slope of 1.0000, an intercept of 0.0000 ppb and an R2 of
1.0000.

Examination of the animations shows that the majority of the differences are occurring in
Canada and the Northern U.S. with the differences occurring in the areas of relatively high
PM2.5. We speculate that the differences are primarily from the difference in the Nitrate and most
likely from different pathways being taken in the ISOROPIA algorithm.

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 143
Table 5-2. Comparison of 2028el CAMx 6.32 Simulation PM2.5 Concentrations (µg/m3)
Run on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum Positive
and Maximum Negative Differences are Shown.
Year Month Day Hour VISTAS
Conc.
EPA
Conc.
Difference
(µg/m3)
Percent
Difference Column Row
Maximum Positive
2011 1 3 4 35.87 30.72 5.15 16.77% 155 237
2011 1 3 12 37.94 33.42 4.53 13.54% 159 237
2011 1 27 7 13.15 8.86 4.29 48.41% 346 245
2011 1 27 9 13.30 9.65 3.65 37.86% 347 245
2011 1 14 6 20.06 16.88 3.17 18.80% 148 237
2011 1 27 12 11.44 8.32 3.12 37.47% 343 245
2011 1 14 4 34.11 31.05 3.07 9.88% 123 244
2011 1 14 9 22.40 19.36 3.04 15.70% 144 240
2011 1 14 2 33.74 30.85 2.89 9.35% 132 243
2011 1 15 13 14.87 12.03 2.84 23.63% 125 222
Maximum Negative
2011 1 27 8 9.38 13.98 -4.61 -32.95% 348 245
2011 1 3 7 33.90 37.85 -3.95 -10.44% 155 235
2011 1 27 5 9.70 13.65 -3.95 -28.92% 345 245
2011 1 27 11 6.80 9.98 -3.18 -31.88% 343 244
2011 1 27 9 8.93 12.11 -3.18 -26.23% 348 244
2011 1 27 10 7.21 10.27 -3.06 -29.78% 343 245
2011 1 27 12 7.26 10.21 -2.96 -28.95% 342 244
2011 1 3 21 16.59 19.10 -2.51 -13.15% 164 231
2011 1 14 3 24.38 26.86 -2.48 -9.24% 137 242
2011 1 27 3 11.37 13.82 -2.45 -17.75% 343 245

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 144
Maximum Positive Difference: January 3 at 400 hours
VISTAS Simulation
Difference (VISTAS-EPA)

Figure 5-22: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Maximum Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 145
Second Highest Positive Difference: January 3 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-23: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Second Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 146
Third Highest Positive Difference: January 27 at 700 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-24: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Third Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 147
Fourth Highest Positive Difference: January 27 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-25: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fourth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 148
Fifth Highest Positive Difference: January 14 at 600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-26: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fifth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 149
Sixth Highest Positive Difference: January 27 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-27: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Sixth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 150
Seventh Highest Positive Difference: January 14 at 400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-28: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Seventh Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 151
Eighth Highest Positive Difference: January 14 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-29: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Eighth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 152
Ninth Highest Positive Difference: January 14 at 200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-30: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Ninth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 153
Tenth Highest Positive Difference: January 15 at 1300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-31: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Tenth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 154
Maximum Negative Difference: January 27 at 800 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-32: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Maximum Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 155
Second Highest Negative Difference: January 3 at 700 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-33: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Second Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 156
Third Highest Negative Difference: January 27 at 500 hours
VISTAS Simulation
Difference (VISTAS-EPA)

Figure 5-34: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Third Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 157
Fourth Highest Negative Difference: January 27 at 1100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-35: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fourth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 158
Fifth Highest Negative Difference: January 27 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-36: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fifth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 159
Sixth Highest Negative Difference: January 27 at 1000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-37: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Sixth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 160
Seventh Highest Negative Difference: January 27 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-38: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Seventh Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 161
Eighth Highest Negative Difference: January 3 at 2100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-39: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Eighth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 162
Ninth Highest Negative Difference: January 14 at 300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-40: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Ninth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 163
Tenth Highest Negative Difference: January 27 at 300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-41: Comparison of PM2.5 Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Tenth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 164

Figure 5-42: Scatterplot Comparing 24-hour Average Predicted PM2.5 Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2028el
Simulations Performed by EPA and VISTAS (Alpine).

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 165
5.3 Sulfate
Sulfate results for the top 10 positive and negative hours are presented in tabular format
in Table 5-3. The maximum positive difference is 0.31 µg/m3 falling to 0.17 µg/m3 for the 10th
high. The maximum negative difference is -0.14 µg/m3 falling to -0.08 µg/m3 for the 10th high.
The maximum positive percent difference from these days is 17.8% and negative percent
difference of -6.8%.

The top 10 positive impact hours are presented in Figures 5-43 through 5-52 and the top
10 negative impact hours are presented in Figures 5-53 through 5-62. The locations of the
impacts are considerably more localized than the PM2.5 differences, and are not occurring in any
systematic location, but are tending to occur in the colder months. The area of the differences
does not appear to be correlated with areas of high Sulfate concentrations.

Scatterplots of the daily average sulfate concentrations in local standard time at the
IMPROVE monitors are presented in Figure 5-63. The EPA results are plotted on the x-axis and
the VISTAS (Alpine) results are plotted on the y-axis. The data has a perfect degree of
correlation with a line of best fit with a slope of 1.0000, an intercept of 0.0000 ppb and an R2 of
1.0000.

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 166
Table 5-3. Comparison of 2028el CAMx 6.32 Simulation Sulfate Concentrations (µg/m3)
Run on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum Positive
and Maximum Negative Differences are Shown.
Year Month Day Hour VISTAS
Conc.
EPA
Conc.
Difference
(µg/m3)
Percent
Difference Column Row
Maximum Positive
2011 1 26 11 2.08 1.77 0.31 17.80% 209 205
2011 12 13 11 4.75 4.45 0.30 6.79% 170 116
2011 11 23 13 3.43 3.17 0.26 8.23% 215 100
2011 1 26 12 2.31 2.06 0.25 11.99% 209 205
2011 3 16 9 5.22 5.00 0.22 4.49% 227 181
2011 11 23 12 3.27 3.06 0.22 7.12% 215 100
2011 3 5 14 3.45 3.24 0.20 6.27% 183 161
2011 1 26 10 1.92 1.73 0.19 10.81% 209 205
2011 3 5 15 3.63 3.45 0.18 5.31% 183 161
2011 3 8 5 3.33 3.16 0.17 5.39% 112 241
Maximum Negative
2011 1 26 9 4.01 4.15 -0.14 -3.26% 375 181
2011 3 20 13 7.25 7.38 -0.13 -1.74% 359 212
2011 12 26 10 1.74 1.87 -0.13 -6.78% 292 115
2011 5 11 12 2.09 2.19 -0.11 -4.80% 274 135
2011 2 17 4 2.68 2.78 -0.10 -3.72% 147 215
2011 4 13 23 3.38 3.48 -0.10 -2.88% 360 162
2011 2 15 14 3.96 4.06 -0.09 -2.31% 246 156
2011 1 18 12 3.62 3.71 -0.09 -2.31% 303 71
2011 2 15 13 4.16 4.24 -0.08 -1.96% 246 156
2011 12 18 11 2.68 2.76 -0.08 -3.00% 282 115

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 167
Maximum Positive Difference: January 26 at 1100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-43: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Maximum Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 168
Second Highest Positive Difference: December 13 at 1100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-44: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Second Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 169
Third Highest Positive Difference: November 23 at 1300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-45: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Third Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 170
Fourth Highest Positive Difference: January 26 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-46: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fourth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 171
Fifth Highest Positive Difference: March 16 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-47: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fifth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 172
Sixth Highest Positive Difference: November 23 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-48: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Sixth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 173
Seventh Highest Positive Difference: March 5 at 1400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-49: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Seventh Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 174
Eighth Highest Positive Difference: January 26 at 1000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-50: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Eighth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 175
Ninth Highest Positive Difference: March 5 at 1500 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-51: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Ninth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 176
Tenth Highest Positive Difference: March 8 at 500 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-52: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Tenth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 177
Maximum Negative Difference: January 26 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-53: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Maximum Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 178
Second Highest Negative Difference: March 20 at 1300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-54: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Second Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 179
Third Highest Negative Difference: December 26 at 1000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-55: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Third Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 180
Fourth Highest Negative Difference: May 11 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-56: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fourth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 181
Fifth Highest Negative Difference: February 17 at 400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-57: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fifth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 182
Sixth Highest Negative Difference: April 13 at 2300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-58: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Sixth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 183
Seventh Highest Negative Difference: February 15 at 1400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-59: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Seventh Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 184
Eighth Highest Negative Difference: January 18 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-60: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Eighth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 185
Ninth Highest Negative Difference: February 15 at 1300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-61: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Ninth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 186
Tenth Highest Negative Difference: December 18 at 1100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-62: Comparison of Sulfate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Tenth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 187

Figure 5-63: Scatterplot Comparing 24-hour Average Predicted Sulfate Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2028el
Simulations Performed by EPA and VISTAS (Alpine).

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 188
5.4 Nitrate
Nitrate results for the top 10 positive and negative hours are presented in tabular format
in Table 5-4. The maximum positive difference is 4.13µg/m3 falling to 2.23 µg/m3 for the 10th
high. The maximum negative difference is -4.28 µg/m3 falling to -1.92 µg/m3 for the 10th high.
The maximum positive percent difference from these days is 116% and negative percent
difference of -52%, both on low Nitrate concentration days.

The top 10 positive impact hours are presented in Figures 5-64 through 5-73 and the top
10 negative impact hours are presented in Figures 5-74 through 5-83. As was discussed in
Section 5.2 for the PM2.5 concentrations, the differences are tending to occur in January along the
northern border in Canada.

Scatterplots of the daily average nitrate concentrations in local standard time at the
IMPROVE monitors are presented in Figure 5-84. The EPA results are plotted on the x-axis and
the VISTAS (Alpine) results are plotted on the y-axis. The data has a perfect degree of
correlation with a line of best fit with a slope of 1.0000, an intercept of 0.0000 ppb and an R2 of
1.0000.

Examination of the animations shows that the majority of the differences are occurring in
Canada and the Northern U.S. with the differences occurring in the areas of relatively high
PM2.5. We speculate that the differences are primarily from the difference in the Particulate
Nitrate and most likely from different pathways being taken in the ISOROPIA algorithm.

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 189
Table 5-4. Comparison of 2028el CAMx 6.32 Simulation Nitrate Concentrations (µg/m3)
Run on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum Positive
and Maximum Negative Differences are Shown.
Year Month Day Hour VISTAS
Conc.
EPA
Conc.
Difference
(µg/m3)
Percent
Difference Column Row
Maximum Positive
2011 1 27 7 7.66 3.54 4.13 116.71% 346 245
2011 1 3 4 25.36 21.37 3.99 18.69% 155 237
2011 1 27 9 8.03 4.38 3.65 83.38% 347 245
2011 1 3 12 26.92 23.41 3.51 14.98% 159 237
2011 1 27 12 6.62 3.55 3.08 86.81% 343 245
2011 1 27 11 6.85 4.05 2.80 69.19% 342 245
2011 1 14 6 14.01 11.55 2.46 21.30% 148 237
2011 1 14 4 24.18 21.80 2.37 10.89% 123 244
2011 1 14 9 15.75 13.39 2.36 17.64% 144 240
2011 1 14 2 23.79 21.56 2.23 10.35% 132 243
Maximum Negative
2011 1 27 8 4.01 8.29 -4.28 -51.60% 348 245
2011 1 27 5 3.91 7.68 -3.77 -49.11% 345 245
2011 1 3 7 23.34 26.41 -3.07 -11.61% 155 235
2011 1 27 9 3.72 6.65 -2.92 -44.00% 348 244
2011 1 27 12 3.03 5.93 -2.89 -48.81% 342 244
2011 1 27 11 2.44 5.14 -2.70 -52.58% 343 244
2011 1 27 10 2.53 5.16 -2.63 -50.89% 343 245
2011 1 27 3 5.12 7.48 -2.35 -31.48% 343 245
2011 1 3 21 10.25 12.20 -1.95 -15.98% 164 231
2011 1 14 3 17.01 18.94 -1.92 -10.15% 137 242

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 190
Maximum Positive Difference: January 27 at 700 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-64: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Maximum Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 191
Second Highest Positive Difference: January 3 at 400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-65: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Second Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 192
Third Highest Positive Difference: January 27 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-66: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Third Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 193
Fourth Highest Positive Difference: January 3 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-67: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fourth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 194
Fifth Highest Positive Difference: January 27 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-68: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fifth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 195
Sixth Highest Positive Difference: January 27 at 1100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-69: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Sixth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 196
Seventh Highest Positive Difference: January 14 at 600 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-70: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Seventh Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 197
Eighth Highest Positive Difference: January 14 at 400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-71: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Eighth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 198
Ninth Highest Positive Difference: January 14 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-72: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Ninth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 199
Tenth Highest Positive Difference: January 14 at 200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-73: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Tenth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 200
Maximum Negative Difference: January 27 at 800 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-74: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Maximum Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 201
Second Highest Negative Difference: January 27 at 500 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-75: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Second Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 202
Third Highest Negative Difference: January 3 at 700 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-76: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Third Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 203
Fourth Highest Negative Difference: January 27 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-77: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fourth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 204
Fifth Highest Negative Difference: January 27 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-78: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Fifth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 205
Sixth Highest Negative Difference: January 27 at 1100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-79: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Sixth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 206
Seventh Highest Negative Difference: January 27 at 1000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-80: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Seventh Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 207
Eighth Highest Negative Difference: January 27 at 300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-81: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Eighth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 208
Ninth Highest Negative Difference: January 3 at 2100 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-82: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Ninth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 209
Tenth Highest Negative Difference: January 14 at 300 hours
VISTAS Simulation

Difference (VISTAS-EPA)
Figure 5-83: Comparison of Nitrate Concentrations (µg/m3) for VISTAS and EPA CAMx
6.32 2028el Simulations (Tenth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 210

Figure 5-84: Scatterplot Comparing 24-hour Average Predicted Nitrate Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 2028el
Simulations Performed by EPA and VISTAS (Alpine).

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 211
5.5 Organic Carbon (OC)
Organic Carbon (OC) results for the top 10 positive and negative hours are presented in
tabular format in Table 5-5. The maximum positive difference is 0.17 µg/m3 falling to 0.09
µg/m3 for the 10th high. The maximum negative difference is -0.30 µg/m3 falling to -0.08 µg/m3
for the 10th high. The maximum positive percent difference from these days is 2.11% and
negative percent difference of -2.86%.

The top 10 positive impact hours are presented in Figures 5-85 through 5-94 and the top
10 negative impact hours are presented in Figures 5-95 through 5-104. The locations of the
impacts are extremely localized.

Scatterplots of the daily average nitrate concentrations in local standard time at the
IMPROVE monitors are presented in Figure 5-105. The EPA results are plotted on the x-axis and
the VISTAS (Alpine) results are plotted on the y-axis. The data has a perfect degree of
correlation with a line of best fit with a slope of 1.0000, an intercept of 0.0000 ppb and an R2 of
1.0000.

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 212
Table 5-5. Comparison of 2028el CAMx 6.32 Simulation Organic Carbon Concentrations
(µg/m3) Run on VISTAS and EPA Computer Systems. Hours with the Top 10 Maximum
Positive and Maximum Negative Differences are Shown.
Year Month Day Hour VISTAS
Conc.
EPA
Conc.
Difference
(µg/m3)
Percent
Difference Column Row
Maximum Positive
2011 6 26 12 16.16 15.99 0.17 1.06% 288 74
2011 5 20 12 11.03 10.90 0.14 1.25% 286 84
2011 8 26 12 10.24 10.11 0.13 1.25% 295 57
2011 5 20 13 10.66 10.54 0.12 1.17% 286 84
2011 12 15 17 25.87 25.76 0.12 0.45% 143 115
2011 7 14 22 4.99 4.89 0.10 2.11% 292 77
2011 8 23 22 7.08 6.98 0.09 1.33% 323 47
2011 6 26 13 11.74 11.65 0.09 0.76% 288 74
2011 7 26 12 9.66 9.57 0.09 0.91% 236 95
2011 8 26 13 7.39 7.30 0.09 1.19% 295 57
Maximum Negative
2011 12 20 9 10.16 10.46 -0.30 -2.86% 313 89
2011 12 20 8 10.43 10.69 -0.25 -2.37% 313 89
2011 5 21 0 7.46 7.56 -0.11 -1.41% 331 95
2011 12 20 10 10.41 10.51 -0.11 -1.00% 313 89
2011 2 14 22 16.01 16.11 -0.10 -0.65% 271 69
2011 2 14 23 18.33 18.43 -0.10 -0.56% 271 69
2011 8 4 14 13.16 13.26 -0.10 -0.74% 213 89
2011 7 19 12 7.01 7.10 -0.09 -1.28% 253 100
2011 7 15 13 5.01 5.09 -0.08 -1.63% 314 98
2011 10 2 15 8.09 8.17 -0.08 -1.00% 136 181

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 213
Maximum Positive Difference: June 26 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-85: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Maximum Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 214
Second Highest Positive Difference: May 20 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-86: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Second Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 215
Third Highest Positive Difference: August 26 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-87: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Third Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 216
Fourth Highest Positive Difference: May 20 at 1300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-88: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Fourth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 217
Fifth Highest Positive Difference: December 15 at 1700 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-89: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Fifth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 218
Sixth Highest Positive Difference: July 14 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-90: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Sixth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 219
Seventh Highest Positive Difference: August 23 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-91: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Seventh Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 220
Eighth Highest Positive Difference: June 26 at 1300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-92: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Eighth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 221
Ninth Highest Positive Difference: July 26 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-93: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Ninth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 222
Tenth Highest Positive Difference: August 26 at 1300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-94: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Tenth Highest Positive Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 223
Maximum Negative Difference: December 20 at 900 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-95: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Maximum Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 224
Second Highest Negative Difference: December 20 at 800 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-96: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Second Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 225
Third Highest Negative Difference: May 21 at 0000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-97: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Third Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 226
Fourth Highest Negative Difference: December 20 at 1000 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-98: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Fourth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 227
Fifth Highest Negative Difference: February 14 at 2200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-99: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and EPA
CAMx 6.32 2028el Simulations (Fifth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 228
Sixth Highest Negative Difference: February 14 at 2300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-100: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and
EPA CAMx 6.32 2028el Simulations (Sixth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 229
Seventh Highest Negative Difference: August 4 at 1400 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-101: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and
EPA CAMx 6.32 2028el Simulations (Seventh Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 230
Eighth Highest Negative Difference: July 19 at 1200 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-102: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and
EPA CAMx 6.32 2028el Simulations (Eighth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 231
Ninth Highest Negative Difference: July 15 at 1300 hours
VISTAS Simulation

Difference (VISTAS-EPA)

Figure 5-103: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and
EPA CAMx 6.32 2028el Simulations (Ninth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 232
Tenth Highest Negative Difference: October 2 at 1500 hours
VISTAS Simulation

Difference (VISTAS-EPA)
Figure 5-104: Comparison of Organic Carbon Concentrations (µg/m3) for VISTAS and
EPA CAMx 6.32 2028el Simulations (Tenth Highest Negative Difference)

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 233

Figure 5-105: Scatterplot Comparing 24-hour Average Predicted Organic Carbon
Concentrations (µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32
2028el Simulations Performed by EPA and VISTAS (Alpine).

CAMx 2011el and 2018el Benchmarking Report – revised draft

August 17, 2020 234
6.0 CONCLUSION
A comparison has been made between 2011el and 2028el CAMx 6.32 simulations
performed on the EPA computer and simulations using the same input files and configuration
performed on the Alpine Geophysics computer system for the VISTAS project. The comparison
was conducted for ozone, PM2.5, sulfate, nitrate and organic carbon and included an examination
both of hourly gridded concentrations, and at daily average concentrations at the IMPROVE
monitors.

The hourly gridded comparison showed limited areas of differences with the location,
date and time of the largest differences being similar for both 2011 and 2028, although the
magnitude of the differences are slightly different. For ozone the maximum differences occurred
suddenly over a limited area and then dispersed over several hours. For particulate species the
differences tended to occur near the northern boundary of the domain in areas with high in-flow
boundary condition. The majority of the differences in total PM2.5 concentrations are due to
wintertime nitrate as a result of different pathway being taken in the ISOROPIA algorithm.

A comparison of the daily average concentrations at the IMPROVE monitors showed
very near perfect agreement with the EPA results with slopes of 1.0000, intercepts at or very near
zero and R2 of 1.0000. Alpine Geophysics has no reservations that the model is operating in a
consistent manner with the simulations performed at EPA.