AQ_GEN_PLNG_20220404_SIP_RH-SIP_AppE2b

Appendix E-2b

Regional Haze Modeling for Southeastern VISTAS II
Regional Haze Analysis Project 2011el CAMx Version
6.32 and 6.40 Comparison Report

Benchmark Run #3

August 17, 2020

This page intentionally left blank.

Regional Haze Modeling for Southeastern
VISTAS II Regional Haze Analysis Project
2011el CAMx Version 6.32 and 6.40
Comparison Report

Task 6 Benchmark Report #2
Covering Benchmark Run #3

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 Benchmarking Report#2

August 17, 2020 i

This page is intentionally blank.

CAMx Benchmarking Report#2

August 17, 2020 ii
Contents
Page
1.0 INTRODUCTION ............................................................................................................1
1.1 Overview ...............................................................................................................1
1.2 2011el CAMx 6.32 and CAMx 6.40 Comparison ................................................3
2.0 DIFFERENCES BETWEEN CAMX 6.32 AND 6.40 SIMULATIONS .........................3
2.1 Model Differences ................................................................................................3
2.2 Configurations Difference ....................................................................................4
3.0 CONFIRMATION METHODOLOGY ............................................................................5
3.1 CAMx Species Mapping .......................................................................................6
4.0 CAMX 6.32 AND CAMX 6.40 2011EL COMPARISON ...............................................6
4.1 Ozone ....................................................................................................................6
4.2 PM2.5 ...................................................................................................................30
4.3 Sulfate .................................................................................................................54
4.4 Nitrate .................................................................................................................77
4.5 Organic Matter (OM) ........................................................................................100
5.0 CONCLUSIONS...........................................................................................................124

CAMx Benchmarking Report#2

August 17, 2020 iii

This page is intentionally blank.

CAMx Benchmarking Report#2

August 17, 2020 iv
TABLES
Table 3-1. Species Mapping from CAMx into Aggregated Species ...............................................6
Table 4-1. Comparison of 2011el CAMx 6.32 and CAMx 6.40 Simulation of Ozone
Concentrations (ppb). Hours with the top 10 maximum positive and maximum
negative differences are shown. ...........................................................................................8
Table 4-2. Comparison of 2011el CAMx 6.32 and CAMx 6.40 Simulation of PM2.5
Concentrations (µg/m3). Hours with the top 10 maximum positive and maximum
negative differences are shown. .........................................................................................31
Table 4-3. Comparison of 2011el CAMx 6.32 and CAMx 6.40 Simulation of Sulfate
Concentrations (µg/m3). Hours with the top 10 maximum positive and maximum
negative differences are shown. .........................................................................................55
Table 4-4. Comparison of 2011el CAMx 6.32 and CAMx 6.40 Simulation of Nitrate
Concentrations (µg/m3). Hours with the top 10 maximum positive and maximum
negative differences are shown. .........................................................................................78
Table 4-5. Comparison of 2011el CAMx 6.32 and CAMx 6.40 Simulation of Organic Matter
Concentrations (µg/m3). Hours with the top 10 maximum positive and maximum
negative differences are shown. .......................................................................................101

FIGURES
Figure 4-1: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Maximum Positive Difference) ..........................................................9
Figure 4-2: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Second Highest Positive Difference) ................................................10
Figure 4-3: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Third Highest Positive Difference)...................................................11
Figure 4-4: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fourth Highest Positive Difference) .................................................12
Figure 4-5: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fifth Highest Positive Difference) ....................................................13
Figure 4-6: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Sixth Highest Positive Difference) ...................................................14
Figure 4-7: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Seventh Highest Positive Difference) ...............................................15
Figure 4-8: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Eighth Highest Positive Difference) .................................................16

CAMx Benchmarking Report#2

August 17, 2020 v
Figure 4-9: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Ninth Highest Positive Difference) ..................................................17
Figure 4-10: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Tenth Highest Positive Difference) ..................................................18
Figure 4-11: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Maximum Negative Difference) .......................................................19
Figure 4-12: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Second Highest Negative Difference) ..............................................20
Figure 4-13: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Third Highest Negative Difference) .................................................21
Figure 4-14: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fourth Highest Negative Difference) ...............................................22
Figure 4-15: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fifth Highest Negative Difference) ..................................................23
Figure 4-16: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Sixth Highest Negative Difference) .................................................24
Figure 4-17: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Seventh Highest Negative Difference) .............................................25
Figure 4-18: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Eighth Highest Negative Difference .................................................26
Figure 4-19: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Ninth Highest Negative Difference) .................................................27
Figure 4-20: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Tenth Highest Negative Difference).................................................28
Figure 4-21: Scatterplot Comparing 24-hour Average Predicted Ozone Concentrations (ppb)
for All Days at all IMPROVE Monitor Locations for CAMx 6.32 and CAMx 6.40
2011el Simulations Performed by VISTAS (Alpine). .......................................................29
Figure 4-22: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Maximum Positive Difference) ........................................................32
Figure 4-23: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Second Highest Positive Difference) ................................................33
Figure 4-24: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Third Highest Positive Difference)...................................................34
Figure 4-25: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fourth Highest Positive Difference) .................................................35
Figure 4-26: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fifth Highest Positive Difference) ....................................................36

CAMx Benchmarking Report#2

August 17, 2020 vi
Figure 4-27: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Sixth Highest Positive Difference) ...................................................37
Figure 4-28: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Seventh Highest Positive Difference) ...............................................38
Figure 4-29: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Eighth Highest Positive Difference) .................................................39
Figure 4-30: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Ninth Highest Positive Difference) ..................................................40
Figure 4-31: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Tenth Highest Positive Difference) ..................................................41
Figure 4-32: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Maximum Negative Difference) .......................................................42
Figure 4-33: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Second Highest Negative Difference) ..............................................43
Figure 4-34: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Third Highest Negative Difference) .................................................44
Figure 4-35: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fourth Highest Negative Difference) ...............................................45
Figure 4-36: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fifth Highest Negative Difference) ..................................................46
Figure 4-37: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Sixth Highest Negative Difference) .................................................47
Figure 4-38: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Seventh Highest Negative Difference) .............................................48
Figure 4-39: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Eighth Highest Negative Difference) ...............................................49
Figure 4-40: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Ninth Highest Negative Difference) .................................................50
Figure 4-41: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Tenth Highest Negative Difference).................................................51
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 and CAMx
6.40 2011el Simulations Performed by VISTAS (Alpine). ...............................................52
Figure 4-43: Scatterplot Comparing 24-hour Average Predicted PM2.5 Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 and CAMx
6.40 2011el Simulations Performed by VISTAS (Alpine); Modified Scale. ....................53

CAMx Benchmarking Report#2

August 17, 2020 vii
Figure 4-44: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Maximum Positive Difference) ........................................................56
Figure 4-45: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Second Highest Positive Difference) ................................................57
Figure 4-46: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Third Highest Positive Difference)...................................................58
Figure 4-47: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fourth Highest Positive Difference) .................................................59
Figure 4-48: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fifth Highest Positive Difference) ....................................................60
Figure 4-49: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Sixth Highest Positive Difference) ...................................................61
Figure 4-50: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations.............................................................................................................62
Figure 4-51: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Eighth Highest Positive Difference) .................................................63
Figure 4-52: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Ninth Highest Positive Difference) ..................................................64
Figure 4-53: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Tenth Highest Positive Difference) ..................................................65
Figure 4-54: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Maximum Negative Difference) .......................................................66
Figure 4-55: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Second Highest Negative Difference) ..............................................67
Figure 4-56: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Third Highest Negative Difference) .................................................68
Figure 4-57: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fourth Highest Negative Difference) ...............................................69
Figure 4-58: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fifth Highest Negative Difference) ..................................................70
Figure 4-59: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Sixth Highest Negative Difference) .................................................71
Figure 4-60: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Seventh Highest Negative Difference) .............................................72
Figure 4-61: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Eighth Highest Negative Difference) ...............................................73
Figure 4-62: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Ninth Highest Negative Difference) .................................................74

CAMx Benchmarking Report#2

August 17, 2020 viii
Figure 4-63: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Tenth Highest Negative Difference).................................................75
Figure 4-64: Scatterplot Comparing 24-hour Average Predicted Sulfate Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 and CAMx
6.40 2011el Simulations Performed by VISTAS (Alpine). ...............................................76
Figure 4-65: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Maximum Positive Difference) ........................................................79
Figure 4-66: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Second Highest Positive Difference) ................................................80
Figure 4-67: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Third Highest Positive Difference)...................................................81
Figure 4-68: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fourth Highest Positive Difference) .................................................82
Figure 4-69: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fifth Highest Positive Difference) ....................................................83
Figure 4-70: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Sixth Highest Positive Difference) ...................................................84
Figure 4-71: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Seventh Highest Positive Difference) ...............................................85
Figure 4-72: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Eighth Highest Positive Difference) .................................................86
Figure 4-73: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Ninth Highest Positive Difference) ..................................................87
Figure 4-74: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Tenth Highest Positive Difference) ..................................................88
Figure 4-75: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Maximum Negative Difference) .......................................................89
Figure 4-76: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Second Highest Negative Difference) ..............................................90
Figure 4-77: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Third Highest Negative Difference) .................................................91
Figure 4-78: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fourth Highest Negative Difference) ...............................................92
Figure 4-79: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fifth Highest Negative Difference) ..................................................93
Figure 4-80: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Sixth Highest Negative Difference) .................................................94

CAMx Benchmarking Report#2

August 17, 2020 ix
Figure 4-81: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Seventh Highest Negative Difference) .............................................95
Figure 4-82: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Eighth Highest Negative Difference) ...............................................96
Figure 4-83: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Ninth Highest Negative Difference) .................................................97
Figure 4-84: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Tenth Highest Negative Difference).................................................98
Figure 4-85: Scatterplot Comparing 24-hour Average Predicted Nitrate Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 and CAMx
6.40 2011el Simulations Performed by VISTAS (Alpine). ...............................................99
Figure 4-86: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Maximum Positive Difference) ..................................102
Figure 4-87: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Second Highest Positive Difference) ..........................103
Figure 4-88: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Third Highest Positive Difference) ............................104
Figure 4-89: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Fourth Highest Positive Difference) ...........................105
Figure 4-90: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Fifth Highest Positive Difference) ..............................106
Figure 4-91: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Sixth Highest Positive Difference) .............................107
Figure 4-92: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Seventh Highest Positive Difference) ........................108
Figure 4-93: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Eighth Highest Positive Difference) ...........................109
Figure 4-94: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Ninth Highest Positive Difference) ............................110
Figure 4-95: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Tenth Highest Positive Difference) ............................111
Figure 4-96: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Maximum Negative Difference) .................................112
Figure 4-97: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Second Highest Negative Difference) ........................113
Figure 4-98: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Third Highest Negative Difference) ...........................114

CAMx Benchmarking Report#2

August 17, 2020 x
Figure 4-99: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Fourth Highest Negative Difference) .........................115
Figure 4-100: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Fifth Highest Negative Difference) ............................116
Figure 4-101: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Sixth Highest Negative Difference) ...........................117
Figure 4-102: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Seventh Highest Negative Difference) .......................118
Figure 4-103: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Eighth Highest Negative Difference) .........................119
Figure 4-104: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Ninth Highest Negative Difference) ...........................120
Figure 4-105: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Tenth Highest Negative Difference) ..........................121
Figure 4-106: Scatterplot Comparing 24-hour Average Predicted Organic Matter
Concentrations (µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx
6.32 and CAMx 6.40 2011el Simulations Performed by VISTAS (Alpine). ..................122
Figure 4-107: Scatterplot Comparing 24-hour Average Predicted Organic Matter
Concentrations (µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx
6.32 and CAMx 6.40 2011el Simulations Performed by VISTAS (Alpine); Modified
Scale. ................................................................................................................................123

CAMx Benchmarking Report#2

August 17, 2020 xi
Abbreviations/Acronym List

Alpine Alpine Geophysics, LLC
CAMx Comprehensive Air quality Model with eXtensions
dv Deciview
ERG Eastern Research Group, Inc.
EPA Environmental Protection Agency
FCRS Crustal fraction of PM
FLM Federal Land Manager
FPRM Fine other primary (diameter ≤ 2.5µm)
FR Federal Register
IMPROVE Interagency Monitoring of Protected Visual Environments
µg/m3 microgram per cubic meter
NAAQS National Ambient Air Quality Standard
NA Sodium
OAQPS Office of Air Quality Planning and Standards
O3 Ozone
OC Organic carbon
OM Organic matter
OSAT Ozone Source Apportionment Technology
PCL Primary chlorine
PEC Primary elemental carbon
PM Particulate matter
PM2.5 Fine particle; primary particulate matter less than or equal to 2.5 microns
in aerodynamic diameter
PNH4 Particulate ammonium
PNO3 Particulate nitrate
POA Primary Organic Aerosol
ppb Parts per billion
PSAT Particulate Source Apportionment Technology
PSO4 Particulate sulfate
R2 Pearson correlation coefficient squared
RADM-AQ Regional Acid Deposition Model – aqueous chemistry
RHR Regional Haze Rule
SESARM Southeastern States Air Resource Managers, Inc.
SIP State Implementation Plan
SO2 Sulfur dioxide
SOA Secondary organic aerosol
SOAP Secondary organic aerosol partitioning
U.S. United States
VISTAS Visibility Improvement – State and Tribal Association of the Southeast

CAMx Benchmarking Report#2

August 17, 2020 1
1.0 INTRODUCTION
1.1 Overview
Southeastern States Air Resource Managers, Inc. (SESARM) has been designated by the
United States (U.S.) Environmental Protection Agency (EPA) as the entity responsible for
coordinating regional haze evaluations for the ten Southeastern states of Alabama, Florida,
Georgia, Kentucky, Mississippi, North Carolina, South Carolina, Tennessee, Virginia, and West
Virginia. The Eastern Band of Cherokee Indians and the Knox County, Tennessee local air
pollution control agency are also participating agencies. These parties are collaborating through
the Regional Planning Organization known as Visibility Improvement - State and Tribal
Association of the Southeast (VISTAS) in the technical analyses and planning activities
associated with visibility and related regional air quality issues. VISTAS analyses will support
the VISTAS states in their responsibility to develop, adopt, and implement their State
Implementation Plans (SIPs) for regional haze.
The state and local air pollution control agencies in the Southeast are mandated to protect
human health and the environment from the impacts of air pollutants. They are responsible for
air quality planning and management efforts including the evaluation, development, adoption,
and implementation of strategies controlling and managing all criteria air pollutants including
fine particles and ozone as well as regional haze. This project will focus on regional haze and
regional haze precursor emissions. Control of regional haze precursor emissions will have the
additional benefit of reducing criteria pollutants as well.
The 1999 Regional Haze Rule (RHR) identified 18 Class I Federal areas (national parks
greater than 6,000 acres and wilderness areas greater than 5,000 acres) in the VISTAS region.
The 1999 RHR required states to define long-term strategies to improve visibility in Federal
Class I national parks and wilderness areas. States were required to establish baseline visibility
conditions for the period 2000-2004, natural visibility conditions in the absence of anthropogenic
influences, and an expected rate of progress to reduce emissions and incrementally improve
visibility to natural conditions by 2064. The original RHR required states to improve visibility on
the 20% most impaired days and protect visibility on the 20% least impaired days.1 The RHR

1 RHR summary data is available at: http://vista.cira.colostate.edu/Improve/rhr-summary-data/

CAMx Benchmarking Report#2

August 17, 2020 2
requires states to evaluate progress toward visibility improvement goals every five years and
submit revised SIPs every ten years.
EPA finalized revisions to various requirements of the RHR in January 2017 (82 FR
3078) that were designed to strengthen, streamline, and clarify certain aspects of the agency’s
regional haze program including:
A. Strengthening the Federal Land Manager (FLM) consultation requirements to ensure that
issues and concerns are brought forward early in the planning process.
B. Updating the SIP submittal deadlines for the second planning period from July 31, 2018
to July 31, 2021 to ensure that they align where applicable with other state obligations
under the Clean Air Act. The end date for the second planning period remains 2028; that
is, the focus of state planning will be to establish reasonable progress goals for each Class
I area against which progress will be measured during the second planning period. This
extension will allow states to incorporate planning for other Federal programs while
conducting their regional haze planning. These other programs include: the Mercury and
Air Toxics Standards, the 2010 1-hour sulfur dioxide (SO2) National Ambient Air
Quality Standards (NAAQS); the 2012 annual fine particle (PM2.5) NAAQS; and the
2008 and 2015 ozone NAAQS.
C. Adjusting interim progress report submission deadlines so that second and subsequent
progress reports will be due by: January 31, 2025; July 31, 2033; and every ten years
thereafter. This means that one progress report will be required midway through each
planning period.
D. Removing the requirement for progress reports to take the form of SIP revisions. States
will be required to consult with FLMs and obtain public comment on their progress
reports before submission to the EPA. EPA will be reviewing but not formally approving
or disapproving these progress reports.
The RHR defines “clearest days” as the 20% of monitored days in a calendar year with
the lowest deciview (dv) index values. “Most impaired days” are defined as the 20% of

CAMx Benchmarking Report#2

August 17, 2020 3
monitored days in a calendar year with the highest amounts of anthropogenic visibility
impairment. The long-term strategy and the reasonable progress goals must provide for an
improvement in visibility for the most impaired days since the baseline period and ensure no
degradation in visibility for the clearest days since the baseline period.
1.2 2011el CAMx 6.32 and CAMx 6.40 Comparison
Recent EPA 2011el and 2028el platform simulations were performed with
Comprehensive Air quality Model with eXtensions (CAMx) version 6.32. Since that time the
CAMx model has been updated to include better physical treatment, and to correct any model
flaws that were discovered after the release of 6.32.
Alpine Geophysics, LLC (Alpine), under subcontract with Eastern Research Group, Inc.
(ERG), has executed two air quality simulations for the 2011el base year modeling platform; one
run with CAMx 6.32 and one with CAMx 6.40. We note that CAMx 6.50 has now been released,
however that model release was too late to be included with sufficient certainty in the VISTAS II
project schedule.
This comparison is to document the differences in model estimates between 2011EL
simulated with CAMx 6.32 and CAMx 6.40 as is discussed in the VISTAS II Modeling
Protocol 2 in Section 6.5.2 model comparison number 3.
2.0 DIFFERENCES BETWEEN CAMX 6.32 AND 6.40 SIMULATIONS
Differences in modeled output concentrations between the CAMx 6.32 and 6.40
simulations were as a result both of changes to the CAMx model code and changes to the model
inputs.
Model Differences
Many updates to the CAMx model were implemented between the 6.32 and 6.40 release.
According to the CAMx 6.40 release notes, the significant changes included:

2 “Regional Haze Modeling for Southeastern VISTAS II Region Haze Analysis Project, Final Modeling Protocol.” Prepared
for SESARM under Contract No. V-2018-03-01. Prepared by Alpine Geophysics, LLC and Eastern Research Group, Inc.
June 27, 2018.

CAMx Benchmarking Report#2

August 17, 2020 4
1. Updates to the chemistry to include a condensed halogen mechanism for ocean-borne
inorganic reactive iodine, hydrolysis of isoprene-derived organic nitrate and SO2
oxidation on primary crustal fine particulate matter (PM). This update includes the
changes to the Ozone and Particulate Source Apportionment Technology (OSAT/PSAT)
algorithms;
2. Inclusion of in-line inorganic iodine emissions to support halogen chemical mechanisms;
3. A major revision to the secondary organic aerosol portioning (SOAP) chemistry/
partitioning algorithm;
4. Updates to the Regional Acid Deposition Model – aqueous chemistry (RADM-AQ)
algorithm; and
5. A major revision to the wet deposition algorithm to identify assumptions or processes
that were unintentionally or otherwise unreasonably limiting gas and PM update into
precipitation. The wet deposition algorithm was simplified and improved in several ways,
resulting in the increased scavenging of gases and PM.
Configurations Difference
In addition to the model version, the CAMx 6.32 and 6.40 simulations contained
differences in the EPA modeling platform that had been made subsequent to the 2011el/2028el
model release. In the most current 2023en simulation, EPA developed new photolysis rates and
ozone column data. These updates were included in the updated modeling platform and resulting
CAMx 6.40 simulation and were used in the VISTAS II 2011el simulations.
Another configuration difference is how the boundary conditions were mapped for
speciation in the two versions of the model. EPA and the VISTAS CAMx 6.32 and 6.40
simulations all used the same boundary condition files. However, when CAMx was updated
from 6.32 to 6.40 the species in the secondary organic aerosol (SOA) scheme changed. The
SOA5, SOA6, and SOA7 were removed and SOA3 and SOA4 were redefined. Neither EPA nor
this study remapped the boundary conditions to account for this change. EPA examined the
regional haze summary data for all Class I areas and found the total organic carbon (OC) species

CAMx Benchmarking Report#2

August 17, 2020 5
(not just SOA) accounted for 1-5% of the boundary condition impairment at the Southeastern
Class I areas.3 This is a small impact on regional haze and the impact of SOA on regional haze is
even smaller.
3.0 CONFIRMATION METHODOLOGY
The presented comparison of model simulations are based on hourly differences in ozone
(O3), PM2.5, Organic Matter (OM), Particulate Nitrate (PNO3), and Particulate Sulfate (PSO4).
The metric for comparison are the absolute difference (Equation 1) and percent difference
(Equation 2) defined as:
(Equation 1) (𝐶𝐶6.32 −𝐶𝐶6.40 )

(Equation 2) (𝐶𝐶6.32−𝐶𝐶6.40 )(𝐶𝐶6.40 )

Where C6.40 is the concentration at each grid cell hour for the CAMx 6.40 simulation and
C6.32 is the concentration at each grid cell hour for the CAMx 6.32 simulation.
The results are presented for the hours with the largest difference between the
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.

3 Brian Timin, EPA Office of Air Quality Planning and Standards (OAQPS) personal communication October 11, 2018.

CAMx Benchmarking Report#2

August 17, 2020 6
CAMx Species Mapping
Updates to the CAMx model between version 6.32 and 6.40 necessitated making changes
to how the individual CAMx species were aggregated to the presented species. The CAMx
species mapping between the two compared versions are presented in Table 3-1.
Table 3-1. Species Mapping from CAMx into Aggregated Species
Aggregated
Species CAMx 6.32 Species CAMx 6.40 Species
Ozone O3 O3
PM2.5
PSO4+PNO3+PNH4+SOA1+SOA2+SOA3
+SOA4+SOA5+SOA6+SOA7+SOPA+SOP
B+POA+PEC+FPRM+FCRS+NA+PCL
PSO4+PNO3+PNH4+SOA1+SOA2
+SOA3+SOA4+SOPA+SOPB+POA
+PEC+FPRM+FCRS+NA+PCL
Sulfate PSO4 PSO4
Nitrate PNO3 PNO3
Organic
Matter (OM)
SOA1+SOA2+SOA3+SOA4+SOA5+SOA6
+SOA7+SOPA+SOPB+POA1
SOA1+SOA2+SOA3+SOA4+SOPA
+SOPB+POA
1 SOAH was not included in the 6.32 comparison since it was not included as an output species in the EPA
simulation.
4.0 CAMX 6.32 AND CAMX 6.40 2011EL COMPARISON
This section presents comparisons of the simulations using CAMx 6.32 and CAMx 6.40
performed on the Alpine computer system using EPA’s 2011el modeling platform.
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 14.48 parts per billion (ppb) falling to 10.47 ppb
for the 10th high. The maximum negative difference is -13.74 ppb falling to -9.61 for the 10th
high. The highest positive differences are occurring on relatively high ozone hours with
concentrations ranging from 80 ppb to 113 ppb for the CAMx 6.32 simulation. The maximum
negative difference days generally are on hours with more modest concentrations of 51 to 72
ppb, except for a July 18th day with a 150 ppb estimate. The maximum positive percent
difference is 18.9% and the maximum negative percent difference is -18.5%.
The top ten positive impact hours are presented in Figures 4-1 through 4-10. The regions
of highest positive differences, meaning that estimates with CAMx 6.32 are higher that CAMx
6.40, tend to occur over the western edge of Lake Michigan. The concentration difference

CAMx Benchmarking Report#2

August 17, 2020 7
summed over the entire domain show a negative concentration, meaning that estimates with
CAMx 6.40 is overall producing more ozone.
The top ten negative impact hours are presented in Figures 4-11 through 4-20. On days
with high negative differences the areas of maximum difference vary hour to hour with the
maximum difference most often over the eastern Gulf of Mexico. On five of the top ten negative
days CAMx 6.32 estimates higher ozone, and on five of the days CAMx 6.40 estimates higher
ozone.
Scatterplots of the daily average ozone concentrations in local standard time at the
Interagency Monitoring of Protected Visual Environments (IMPROVE) monitors across all
modeled days are presented in Figure 4-21. The CAMx 6.40 results are plotted on the x-axis and
the CAMx 6.32 results are plotted on the y-axis. The data has a high degree of correlation with a
line of best fit with a slope of 0.9975, an intercept of 0.0592 ppb and an R2 of 0.9995.
Examination of the animations show that in general CAMx 6.32 makes more ozone in the
southern U.S. and intermountain west, and CAMx 6.40 makes more ozone in the northern U.S.

CAMx Benchmarking Report#2

August 17, 2020 8
Table 4-1. Comparison of 2011el CAMx 6.32 and CAMx 6.40 Simulation of Ozone
Concentrations (ppb). Hours with the top 10 maximum positive and maximum negative
differences are shown.
Year Month Day Hour 6.32
Conc.
6.40
Conc.
Difference
(ppb)
Percent
Difference Column Row
Maximum Positive
2011 6 18 19 112.01 97.54 14.48 14.8% 266 159
2011 6 18 20 108.71 94.81 13.90 14.7% 266 158
2011 5 22 21 96.36 83.07 13.29 16.0% 264 170
2011 5 30 20 98.40 85.45 12.95 15.2% 263 170
2011 5 22 20 94.40 81.49 12.91 15.8% 265 169
2011 5 30 19 79.99 67.27 12.73 18.9% 263 170
2011 5 22 19 85.52 73.75 11.78 16.0% 266 166
2011 5 22 22 95.40 83.90 11.50 13.7% 264 171
2011 6 18 18 97.04 86.28 10.76 12.5% 267 159
2011 6 18 17 113.30 102.83 10.47 10.2% 374 171
Maximum Negative
2011 4 11 17 60.41 74.16 -13.74 -18.5% 327 56
2011 4 11 18 65.23 77.66 -12.43 -16.0% 327 57
2011 4 11 16 74.52 85.97 -11.45 -13.3% 321 31
2011 7 18 15 150.15 161.50 -11.35 -7.0% 230 239
2011 5 13 21 61.51 72.62 -11.11 -15.3% 224 37
2011 5 13 20 61.36 72.25 -10.89 -15.1% 225 38
2011 4 11 19 72.21 82.25 -10.04 -12.2% 330 42
2011 4 11 20 51.39 61.28 -9.89 -16.1% 220 37
2011 4 12 0 50.55 60.29 -9.74 -16.2% 46 91
2011 4 11 21 60.86 70.47 -9.61 -13.6% 221 36

CAMx Benchmarking Report#2

August 17, 2020 9
Maximum Positive Difference: June 18 at 1900 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-1: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Maximum Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 10
Second Highest Positive Difference: June 18 at 2000 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-2: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Second Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 11
Third Highest Positive Difference: May 22 at 2100 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-3: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Third Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 12
Fourth Highest Positive Difference: May 30 at 2000 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-4: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fourth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 13
Fifth Highest Positive Difference: May 22 at 2000 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-5: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fifth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 14
Sixth Highest Positive Difference: May 30 at 1900 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-6: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Sixth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 15
Seventh Highest Positive Difference: May 22 at 1900 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-7: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Seventh Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 16
Eighth Highest Positive Difference: May 22 at 2200 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-8: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Eighth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 17
Ninth Highest Positive Difference: June 18 at 1800 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-9: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Ninth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 18
Tenth Highest Positive Difference: June 18 at 1700 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-10: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Tenth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 19
Maximum Negative Difference: April 11 at 1700 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-11: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Maximum Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 20
Second Highest Negative Difference: April 11 at 1800 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-12: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Second Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 21
Third Highest Negative Difference: April 11 at 1600 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-13: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Third Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 22
Fourth Highest Negative Difference: July 18 at 1500 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-14: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fourth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 23
Fifth Highest Negative Difference: May 13 at 2100 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-15: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fifth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 24
Sixth Highest Negative Difference: May 13 at 2000 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-16: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Sixth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 25
Seventh Highest Negative Difference: April 11 at 1900 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-17: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Seventh Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 26
Eighth Highest Negative Difference: April 11 at 2000 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-18: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Eighth Highest Negative Difference

CAMx Benchmarking Report#2

August 17, 2020 27
Ninth Highest Negative Difference: April 12 at 0000 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-19: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Ninth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 28
Tenth Highest Negative Difference: April 11 at 2100 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-20: Comparison of Ozone Concentrations (ppb) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Tenth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 29

Figure 4-21: Scatterplot Comparing 24-hour Average Predicted Ozone Concentrations
(ppb) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 and CAMx 6.40
2011el Simulations Performed by VISTAS (Alpine).

CAMx Benchmarking Report#2

August 17, 2020 30
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 64.76 micrograms per cubic meter (µg/m3)
falling to 52.61 µg/m3 for the 10th high. The maximum negative difference is -35.09 µg/m3
falling to -18.42 µg/m3 for the 10th high. The maximum positive percent difference from these
days is 1445% and negative percent difference of -59%. On the day of the maximum positive
difference (September 24 at 0400) the maximum difference in PM2.5 concentration was
64. µg/m3 ppb. At this hour the difference in the sulfate, nitrate, and OM concentrations were
10.26 µg/m3, 28.08 µg/m3, 9.28 µg/m3, respectively with the difference dominated by the
differences in the nitrate estimates.
The top 10 positive difference hours are presented in Figures 4-22 through 4-31. The
hours of the maximum positive difference are tending to occur in two periods on August 26 and
September 24. The CAMx 6.40 results are significantly lower that CAMx 6.32 throughout the
majority of the domain. On August 26 the region of the maximum difference is offshore of
Florida, Georgia, and South Carolina. This appears to be Hurricane Irene that was active during
this time
The top 10 negative impact hours are presented in Figures 4-32 through 4-41. While the
majority of the domain shows positive difference (CAMx 6.32 with higher concentrations), there
are scattered regions where CAMx 6.40 is higher.
Scatterplots of the daily average PM2.5 concentrations in local standard time at the
IMPROVE monitors are presented in Figures 4-42 and 4-43. The CAMx 6.40 results are plotted
on the x-axis and the CAMx 6.32 results are plotted on the y-axis. The data has a high degree of
correlation with a line of best fit with a slope of 1.0083, an intercept of 0.4966 µg/m3and an R2
of 0.9875. The agreement between the models is higher at higher concentrations. At lower
concentrations the CAMx 6.32 results are higher than the CAMx 6.40 results.
Examination of the animations clearly shows the Hurricane Irene entering the domain on
August 24th and moving up the eastern seaboard through August 28th.

CAMx Benchmarking Report#2

August 17, 2020 31
Table 4-2. Comparison of 2011el CAMx 6.32 and CAMx 6.40 Simulation of PM2.5
Concentrations (µg/m3). Hours with the top 10 maximum positive and maximum negative
differences are shown.
Year Month Day Hour 6.32
Conc.
6.40
Conc.
Difference
(µg/m3)
Percent
Difference Column Row
Maximum Positive
2011 9 24 4 69.24 4.48 64.76 1445.0% 342 201
2011 9 24 3 72.57 10.31 62.27 604.0% 343 201
2011 8 26 14 71.90 11.64 60.27 517.9% 358 62
2011 9 24 5 63.70 5.32 58.37 1096.3% 342 200
2011 8 26 12 73.55 15.55 58.00 373.0% 359 58
2011 8 26 13 74.13 17.34 56.79 327.5% 359 60
2011 8 26 15 67.82 12.01 55.81 464.5% 357 64
2011 8 26 17 68.07 13.57 54.49 401.5% 357 69
2011 8 26 16 85.96 32.42 53.54 165.2% 357 68
2011 8 26 20 64.19 11.58 52.61 454.3% 355 75
Maximum Negative
2011 7 20 14 4,665.24 4,700.33 -35.09 -0.7% 231 244
2011 7 20 12 6,908.06 6,937.38 -29.32 -0.4% 231 244
2011 7 20 13 5,435.89 5,464.69 -28.79 -0.5% 231 244
2011 7 20 11 8,766.18 8,789.09 -22.92 -0.3% 231 243
2011 7 20 15 5,136.34 5,157.34 -21.00 -0.4% 230 243
2011 7 20 18 1,471.59 1,492.23 -20.64 -1.4% 227 244
2011 7 3 21 12.76 31.44 -18.68 -59.4% 269 156
2011 8 19 5 80.11 98.72 -18.61 -18.9% 216 52
2011 7 3 22 13.37 31.92 -18.54 -58.1% 269 156
2011 7 20 19 1,215.64 1,234.06 -18.42 -1.5% 226 244

CAMx Benchmarking Report#2

August 17, 2020 32
Maximum Positive Difference: September 24 at 400 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-22: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Maximum Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 33
Second Highest Positive Difference: September 24 at 300 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-23: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Second Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 34
Third Highest Positive Difference: August 26 at 1400 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-24: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Third Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 35
Fourth Highest Positive Difference: September 24 at 500 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-25: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fourth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 36
Fifth Highest Positive Difference: August 26 at 1200 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-26: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fifth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 37
Sixth Highest Positive Difference: August 26 at 1300 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-27: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Sixth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 38
Seventh Highest Positive Difference: August 26 at 1500 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-28: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Seventh Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 39
Eighth Highest Positive Difference: August 26 at 1700 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-29: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Eighth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 40
Ninth Highest Positive Difference: August 26 at 1600 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-30: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Ninth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 41
Tenth Highest Positive Difference: August 26 at 2000 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-31: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Tenth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 42
Maximum Negative Difference: July 20 at 1400 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-32: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Maximum Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 43
Second Highest Negative Difference: July 20 at 1200 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-33: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Second Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 44
Third Highest Negative Difference: July 20 at 1300 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-34: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Third Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 45
Fourth Highest Negative Difference: July 20 at 1100 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-35: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fourth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 46
Fifth Highest Negative Difference: July 20 at 1500 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-36: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Fifth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 47
Sixth Highest Negative Difference: July 20 at 1800 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-37: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Sixth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 48
Seventh Highest Negative Difference: July 3 at 2100 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-38: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Seventh Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 49
Eighth Highest Negative Difference: August 19 at 500 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-39: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Eighth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 50
Ninth Highest Negative Difference: July 3 at 2200 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-40: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Ninth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 51
Tenth Highest Negative Difference: July 20 at 1900 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-41: Comparison of PM2.5 Concentrations (µg/m3) for CAMx 6.32 and CAMx 6.40
2011el Simulations (Tenth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 52

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 and CAMx 6.40
2011el Simulations Performed by VISTAS (Alpine).

CAMx Benchmarking Report#2

August 17, 2020 53

Figure 4-43: Scatterplot Comparing 24-hour Average Predicted PM2.5 Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 and CAMx 6.40
2011el Simulations Performed by VISTAS (Alpine); Modified Scale.

CAMx Benchmarking Report#2

August 17, 2020 54
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 23.32 µg/m3 falling to 14.769 µg/m3 for the
10th high. The maximum negative difference is -17.77 µg/m3 falling to -5.76 µg/m3 for the 10th
high. The maximum positive percent difference from these days is 171% and negative percent
difference of -26.9%.
The top 10 positive difference hours are presented in Figures 4-44 through 4-53. The
regions of the maximum impact are highly variable. The maximum and several other days shows
the maximum difference is located near the Chicago metro area. The second and third highest
maximum and other days show impacts along the Gulf of Mexico coast.
The top 10 negative difference hours are presented in Figures 4-54 through 4-63. The
maximum negative differences for all but one day are occurring on July 20 or 21 along the
northern U.S. border, north of Minnesota.
Scatterplots of the daily average sulfate concentrations in local standard time at the
IMPROVE monitors are presented in Figure 4-64. The CAMx 6.40 results are plotted on the
x-axis and the CAMx 6.32 results are plotted on the y-axis. The data has considerably more
scatter than the ozone or PM2.5 results with a line of best fit with a slope of 1.0842, an intercept
of 0.0832 µg/m3 and an R2 of 0.9068. The vast majority of the points are above the 1:1 line,
meaning that the CAMx 6.32 modeled values are higher than the CAMx 6.40 results. This is
likely a result of the changes in the wet deposition algorithms and the oxidation of SO2 on
primary crustal particles and updates to the RADM-AQ algorithm.
Examination of the CAMx 6.40 animations show generally lower concentrations
compared to CAMx 6.32, particularly in the Southeastern U.S.

CAMx Benchmarking Report#2

August 17, 2020 55
Table 4-3. Comparison of 2011el CAMx 6.32 and CAMx 6.40 Simulation of Sulfate
Concentrations (µg/m3). Hours with the top 10 maximum positive and maximum negative
differences are shown.
Year Month Day Hour 6.32
Conc.
6.40
Conc.
Difference
(µg/m3)
Percent
Difference Column Row
Maximum Positive
2011 12 30 21 44.45 21.13 23.32 110.4% 265 157
2011 5 12 11 71.22 51.23 19.99 39.0% 258 45
2011 5 8 9 43.25 23.36 19.88 85.1% 258 45
2011 12 21 14 46.03 27.37 18.66 68.2% 316 176
2011 3 16 1 29.04 10.70 18.34 171.5% 291 145
2011 5 12 12 75.61 60.06 15.55 25.9% 258 45
2011 5 9 10 42.96 27.94 15.02 53.7% 258 45
2011 12 30 22 45.61 30.69 14.92 48.6% 265 157
2011 5 12 10 56.99 42.11 14.88 35.3% 258 45
2011 5 20 3 26.13 11.37 14.76 129.8% 352 206
Maximum Negative
2011 7 20 12 87.16 104.93 -17.77 -16.9% 231 244
2011 7 20 11 95.08 109.81 -14.72 -13.4% 231 244
2011 7 20 13 68.92 82.16 -13.24 -16.1% 231 244
2011 7 20 14 59.18 69.69 -10.51 -15.1% 231 244
2011 7 21 3 67.32 77.08 -9.76 -12.7% 230 244
2011 7 21 2 108.88 117.08 -8.19 -7.0% 230 243
2011 7 20 15 43.94 51.06 -7.11 -13.9% 231 244
2011 7 21 4 35.42 42.46 -7.05 -16.6% 230 245
2011 7 20 10 94.54 100.83 -6.29 -6.2% 231 241
2011 1 4 18 15.63 21.39 -5.76 -26.9% 170 29

CAMx Benchmarking Report#2

August 17, 2020 56
Maximum Positive Difference: December 30 at 2100 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-44: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Maximum Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 57
Second Highest Positive Difference: May 12 at 1100 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-45: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Second Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 58
Third Highest Positive Difference: May 8 at 900 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-46: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Third Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 59
Fourth Highest Positive Difference: December 21 at 1400 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-47: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Fourth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 60
Fifth Highest Positive Difference: March 16 at 100 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-48: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Fifth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 61
Sixth Highest Positive Difference: May 12 at 1200 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-49: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Sixth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 62
Seventh Highest Positive Difference: May 9 at 1000 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-50: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations

CAMx Benchmarking Report#2

August 17, 2020 63
Eighth Highest Positive Difference: December 30 at 2200 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-51: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Eighth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 64
Ninth Highest Positive Difference: May 12 at 1000 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-52: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Ninth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 65
Tenth Highest Positive Difference: May 20 at 300 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-53: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Tenth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 66
Maximum Negative Difference: July 20 at 1200 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-54: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Maximum Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 67
Second Highest Negative Difference: July 20 at 1100 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-55: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Second Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 68
Third Highest Negative Difference: July 20 at 1300 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-56: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Third Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 69
Fourth Highest Negative Difference: July 20 at 1400 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-57: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Fourth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 70
Fifth Highest Negative Difference: July 21 at 300 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-58: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Fifth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 71
Sixth Highest Negative Difference: July 21 at 200 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-59: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Sixth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 72
Seventh Highest Negative Difference: July 20 at 1500 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-60: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Seventh Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 73
Eighth Highest Negative Difference: July 21 at 400 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-61: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Eighth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 74
Ninth Highest Negative Difference: July 20 at 1000 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-62: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Ninth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 75
Tenth Highest Negative Difference: January 4 at 1800 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-63: Comparison of Sulfate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Tenth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 76

Figure 4-64: Scatterplot Comparing 24-hour Average Predicted Sulfate Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 and CAMx 6.40
2011el Simulations Performed by VISTAS (Alpine).

CAMx Benchmarking Report#2

August 17, 2020 77
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 28.08 µg/m3 falling to 21.00 µg/m3 for the
10th high. The maximum negative difference is -7.05 µg/m3 falling to -6.16 µg/m3 for the 10th
high. The maximum positive percent difference from these days is 2512% and negative percent
difference of -79.6%.
The top 10 positive difference hours are presented in Figures 4-65 through 4-74. The
maximum positive difference hours all occur on either September 24th or May 14th. On
September 24th the peak impacts are in Canada just north of the New York border. On May 14th
the peak impacts are again in Canada, but somewhat further west, north of Lake Erie.
The top 10 negative difference hours are presented in Figures 4-75 through 4-84. The
peak hours are either on January 25th, January 26th, or February 1. For the January days the peak
impact is occurring in southern Indiana. For the February day the peak impact is in eastern
Oklahoma. These are both areas for high local nitrate concentrations in CAMx 6.40.
Scatterplots of the daily average nitrate concentrations in local standard time at the
IMPROVE monitors are presented in Figure 4-85. The CAMx 6.40 results are plotted on the x-
axis and the CAMx 6.32 results are plotted on the y-axis. The data has considerably more scatter
than the ozone or PM2.5 results with a line of best fit with a slope of 0.9276, an intercept of
0.0013 µg/m3 and an R2 of 0.9635. Unlike the sulfate results which showed the CAMx 6.32
results nearly uniformly higher that CAMx 6.40, the nitrate results show more uniform scatter
around the 1:1 line. Nitrate in most inland areas of the eastern U.S. appears slightly higher in
v6.4 during the majority of hours. Superimposed on this slight increase there are occasional
periods where when CAMx 6.40 is lower than CAMx 6.32, and other periods when CAMx 6.40
is higher than CAMx 6.32. The net results demonstrate a fairly uniform scatter around the 1:1
line.

CAMx Benchmarking Report#2

August 17, 2020 78
Table 4-4. Comparison of 2011el CAMx 6.32 and CAMx 6.40 Simulation of Nitrate
Concentrations (µg/m3). Hours with the top 10 maximum positive and maximum negative
differences are shown.
Year Month Day Hour 6.32
Conc.
6.40
Conc.
Difference
(µg/m3)
Percent
Difference Column Row
Maximum Positive
2011 9 24 4 30.90 2.82 28.08 997.3% 342 201
2011 9 24 3 32.93 5.53 27.40 495.7% 343 201
2011 5 14 13 31.25 4.39 26.86 611.1% 306 181
2011 5 14 14 27.89 1.67 26.22 1570.6% 305 182
2011 5 14 15 26.94 1.03 25.91 2512.0% 305 182
2011 9 24 5 29.33 3.63 25.70 708.6% 342 200
2011 5 14 12 33.53 8.61 24.92 289.6% 306 181
2011 5 14 16 24.38 1.67 22.71 1362.8% 305 182
2011 5 14 11 33.01 10.58 22.43 211.9% 306 180
2011 9 24 6 27.46 6.47 21.00 324.7% 341 199
Maximum Negative
2011 1 25 22 2.57 9.62 -7.05 -73.3% 274 122
2011 1 25 21 4.19 11.19 -7.00 -62.5% 274 123
2011 1 25 23 2.75 9.67 -6.92 -71.6% 274 120
2011 1 25 20 5.50 12.17 -6.68 -54.9% 274 123
2011 1 26 0 2.61 9.27 -6.66 -71.9% 274 119
2011 2 1 6 1.68 8.23 -6.55 -79.6% 220 92
2011 2 1 5 1.56 8.08 -6.52 -80.7% 219 92
2011 1 25 19 6.37 12.59 -6.22 -49.4% 274 124
2011 1 26 3 4.80 10.99 -6.20 -56.4% 279 149
2011 2 1 4 2.68 8.84 -6.16 -69.6% 211 86

CAMx Benchmarking Report#2

August 17, 2020 79
Maximum Positive Difference: September 24 at 400 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-65: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Maximum Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 80
Second Highest Positive Difference: September 24 at 300 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-66: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Second Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 81
Third Highest Positive Difference: May 14 at 1300 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-67: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Third Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 82
Fourth Highest Positive Difference: May 14 at 1400 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-68: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Fourth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 83
Fifth Highest Positive Difference: May 14 at 1500 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-69: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Fifth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 84
Sixth Highest Positive Difference: September 24 at 500 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-70: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Sixth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 85
Seventh Highest Positive Difference: May 14 at 1200 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-71: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Seventh Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 86
Eighth Highest Positive Difference: May 14 at 1600 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-72: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Eighth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 87
Ninth Highest Positive Difference: May 14 at 1100 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-73: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Ninth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 88
Tenth Highest Positive Difference: September 24 at 600 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-74: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Tenth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 89
Maximum Negative Difference: January 25 at 2200 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-75: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Maximum Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 90
Second Highest Negative Difference: January 25 at 2100 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-76: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Second Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 91
Third Highest Negative Difference: January 25 at 2300 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-77: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Third Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 92
Fourth Highest Negative Difference: January 25 at 2000 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-78: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Fourth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 93
Fifth Highest Negative Difference: January 26 at 0000 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-79: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Fifth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 94
Sixth Highest Negative Difference: February 1 at 600 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-80: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Sixth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 95
Seventh Highest Negative Difference: February 1 at 500 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-81: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Seventh Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 96
Eighth Highest Negative Difference: January 25 at 1900 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-82: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Eighth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 97
Ninth Highest Negative Difference: January 26 at 300 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-83: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Ninth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 98
Tenth Highest Negative Difference: February 1 at 400 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-84: Comparison of Nitrate Concentrations (µg/m3) for CAMx 6.32 and CAMx
6.40 2011el Simulations (Tenth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 99

Figure 4-85: Scatterplot Comparing 24-hour Average Predicted Nitrate Concentrations
(µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32 and CAMx 6.40
2011el Simulations Performed by VISTAS (Alpine).

CAMx Benchmarking Report#2

August 17, 2020 100
4.5 Organic Matter (OM)
Organic Matter (OM) results for the top 10 positive and negative hours are presented in
tabular format in Table 4-5. The maximum positive difference is 30.29 µg/m3 falling to
25.25 µg/m3 for the 10th high. The maximum negative difference is -28.67 µg/m3 falling to -
16.60 µg/m3 for the 10th high. The maximum positive percent difference from these days is
801% and negative percent difference of -80%.
The top 10 positive difference hours are presented in Figures 4-86 through 4-95. The
differences on the two highest days are in the Pacific Northwest. On other days the peaks are
scattered across Southern Canada, north of New York and the south eastern U.S.
The top 10 negative impact hours are presented in Figures 4-96 through 4-105. Five of
the top ten hours occur on July 20th. On this day the location of the peak is along the northern
border of the U.S., north of Minnesota. This is an area where CAMx simulations are showing
very high OM concentrations and an area heavily influenced by boundary conditions. As was
discussed in Section 2, the SOA species definitions changed between CAMx 6.32 and 6.40, but
the mapping of the boundary conditions was not updated between model versions to reflect this
change. This difference in boundary condition species mapping is likely the reason for the
concentration deltas. On July 3, the peak difference is over Lake Michigan; on August 19 the
peak is in eastern Texas.
Scatterplots of the daily average organic matter concentrations in local standard time at
the IMPROVE monitors are presented in Figures 4-106 and 4-107. The CAMx 6.40 results are
plotted on the x-axis and the CAMx 6.32 results are plotted on the y-axis. The data has a high
degree of correlation with a line of best fit with a slope of 1.0122, an intercept of 0.2973 ppb and
an R2 of 0.983.
Examination of the animations reveals that away from frontal boundaries and low
pressure areas, OM in CAMx 6.40 is generally slightly lower compared to CAMx 6.32. While
near frontal boundaries and low pressure areas the opposite is true. These positive and negative
difference seem to balance give a high degree of correlation between the model versions.

CAMx Benchmarking Report#2

August 17, 2020 101
Table 4-5. Comparison of 2011el CAMx 6.32 and CAMx 6.40 Simulation of Organic Matter
Concentrations (µg/m3). Hours with the top 10 maximum positive and maximum negative
differences are shown.
Year Month Day Hour 6.32
Conc.
6.40
Conc.
Difference
(µg/m3)
Percent
Difference Column Row
Maximum Positive
2011 11 3 6 70.40 40.11 30.29 75.5% 38 213
2011 11 3 5 70.91 41.19 29.72 72.2% 39 214
2011 12 6 2 57.66 29.11 28.55 98.1% 354 207
2011 5 21 11 33.46 5.75 27.71 481.9% 226 47
2011 12 6 1 62.13 34.78 27.35 78.6% 353 209
2011 1 26 15 57.93 30.97 26.96 87.1% 314 125
2011 12 6 3 39.21 12.97 26.24 202.3% 355 207
2011 1 26 16 63.39 37.28 26.11 70.0% 314 125
2011 5 21 12 28.46 3.16 25.30 801.3% 225 48
2011 5 21 10 33.98 8.73 25.25 289.4% 226 47
Maximum Negative
2011 7 20 15 3,944.01 3,972.68 -28.67 -0.7% 230 243
2011 7 20 14 3,589.46 3,616.33 -26.88 -0.7% 231 244
2011 7 20 16 3,261.57 3,285.59 -24.02 -0.7% 230 243
2011 7 3 21 4.58 23.21 -18.63 -80.3% 269 156
2011 8 19 5 72.72 91.27 -18.55 -20.3% 216 52
2011 7 3 22 4.62 23.11 -18.50 -80.0% 269 156
2011 7 20 17 1,657.89 1,675.83 -17.94 -1.1% 229 244
2011 7 20 13 2,382.39 2,399.65 -17.26 -0.7% 231 245
2011 7 3 20 4.43 21.62 -17.18 -79.5% 269 156
2011 8 19 6 70.62 87.22 -16.60 -19.0% 216 52

CAMx Benchmarking Report#2

August 17, 2020 102
Maximum Positive Difference: November 3 at 600 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-86: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Maximum Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 103
Second Highest Positive Difference: November 3 at 500 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-87: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Second Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 104
Third Highest Positive Difference: December 6 at 200 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-88: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Third Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 105
Fourth Highest Positive Difference: May 21 at 1100 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-89: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Fourth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 106
Fifth Highest Positive Difference: December 6 at 100 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-90: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Fifth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 107
Sixth Highest Positive Difference: January 26 at 1500 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-91: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Sixth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 108
Seventh Highest Positive Difference: December 6 at 300 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-92: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Seventh Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 109
Eighth Highest Positive Difference: January 26 at 1600 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-93: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Eighth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 110
Ninth Highest Positive Difference: May 21 at 1200 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-94: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Ninth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 111
Tenth Highest Positive Difference: May 21 at 1000 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-95: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Tenth Highest Positive Difference)

CAMx Benchmarking Report#2

August 17, 2020 112
Maximum Negative Difference: July 20 at 1500 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-96: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Maximum Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 113
Second Highest Negative Difference: July 20 at 1400 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-97: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Second Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 114
Third Highest Negative Difference: July 20 at 1600 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-98: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Third Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 115
Fourth Highest Negative Difference: July 3 at 2100 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-99: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Fourth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 116
Fifth Highest Negative Difference: August 19 at 500 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-100: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Fifth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 117
Sixth Highest Negative Difference: July 3 at 2200 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-101: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Sixth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 118
Seventh Highest Negative Difference: July 20 at 1700 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-102: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Seventh Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 119
Eighth Highest Negative Difference: July 20 at 1300 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-103: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Eighth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 120
Ninth Highest Negative Difference: July 3 at 2000 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-104: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Ninth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 121
Tenth Highest Negative Difference: August 19 at 600 hours
CAMx 6.40
Difference (6.32 - 6.40)

Figure 4-105: Comparison of Organic Matter Concentrations (µg/m3) for CAMx 6.32 and
CAMx 6.40 2011el Simulations (Tenth Highest Negative Difference)

CAMx Benchmarking Report#2

August 17, 2020 122

Figure 4-106: Scatterplot Comparing 24-hour Average Predicted Organic Matter
Concentrations (µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32
and CAMx 6.40 2011el Simulations Performed by VISTAS (Alpine).

CAMx Benchmarking Report#2

August 17, 2020 123

Figure 4-107: Scatterplot Comparing 24-hour Average Predicted Organic Matter
Concentrations (µg/m3) for All Days at all IMPROVE Monitor Locations for CAMx 6.32
and CAMx 6.40 2011el Simulations Performed by VISTAS (Alpine); Modified Scale.

CAMx Benchmarking Report#2

August 17, 2020 124
5.0 CONCLUSIONS
A comparison has been made between CAMx 6.32 and CAMx 6.40 simulations using
EPA’s 2011el modeling platform as 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 areas of differences across the domain that varied
hour to hour with the maximum hourly differences varying greatly.
A comparison of the daily average concentrations at the IMPROVE monitors showed
fairly small differences for ozone and OM. For sulfate, the CAMx 6.40 results were generally
lower than CAMx 6.32. For nitrate, the CAMx 6.32 and CAMx 6.40 results differed, with
neither version of the model consistently higher than the other. There appears to be a trend where
CAMx 6.40 is generally slightly higher that CAMx 6.32 during dry periods, but CAMx 6.32 is
generally slightly higher during wet periods. The PM2.5 results generally showed higher CAMx
6.32 concentrations compared to CAMx 6.40 at lower concentration levels, with consistent
results at higher concentrations.
The comparison of CAMx 6.32 and 6.40 showed differences in model concentration
estimates. This is to be expected given the changes to the model from the inclusion of new
science into CAMx 6.40 over that which was included in CAMx 6.32. Alpine does not see any
features in the modeling that would preclude the use of the better science in CAMx 6.40 for use
in the VISTAS air quality planning.