Agenda Item V-2_PowerPoint

NC Exceptional Events Demonstration
for the Revised PM2.5 NAAQS
Presented by Sara Kreuser, Division of Air QualityAir Quality Committee Meeting
January 8, 2025
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Today we’ll cover…
•2024 Revised Primary Annual PM2.5 NAAQS
•2023 Canadian Wildfires
•North Carolina’s Exceptional Events Demonstration
•Key Messages
•Timeline
PM2.5 NAAQS
Key Terminology
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•3 consecutive years of data are used to evaluate a monitor’s status – this is called the Design Value
(e.g., for evaluating our status for 2024, we look at 2021-2023 certified data)
•The 24-hour design value (DV) is the 3-year average of the 98th percentile of 24-hour concentrations
•The annual DV is the 3-year average of the annual concentrations
•Exceedances vs. Violations
•A daily or annual average concentration above either standard is an exceedance
•A design value above either standard is a violation
•We can have exceedances without violating a standard
24-Hour (Daily) Standard
35.5 µg/m3
Average of hourly measurements
from midnight to midnight
Annual Standard
9.0 µg/m3
Average of daily values
from Jan 1 to Dec 31
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Design values at the Remount (Mecklenburg County) and Lexington (Davidson
County) monitors are above the revised annual PM2.5 NAAQS of 9.0 µg/m3
PM2.5 NAAQS Current Status
NC Department of Environmental Quality
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OUR AIR IN NORTH CAROLINA
Residential
Fuel CombustionUnpaved road
NC Department of Environmental Quality5
6 NC Department of Environmental Quality6
“The word ‘unprecedented’ doesn’t do justice to the
severity of the wildfires in Canada this year,” says Yan
Boulanger, research scientist in forest ecology at
Natural Resources Canada. “From a scientific
perspective, the doubling of the previous burned area
record is shocking.” 1
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1. https://natural-resources.canada.ca/simply-science/canadas-record-breaking-wildfires-2023-fiery-wake-call/25303
Graph courtesy https://ciffc.net/statistics
2023 Canadian Wildfires
2.5 mHA burned
on average
17.3 mHA burned
in 2023
NC Department of Environmental Quality
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2023 Canadian Wildfires
How it started
•Persistent, large area of high
pressure over Canada in spring led
to increased drought conditions.
•Resulted in unusually hot and dry
conditions
•Favorable conditions for rapid wildfire
development
•Canadian drought
conditions expanded in June 2023.​
•60% of CA abnormally dry or worse
May 2023 Large Scale Atmospheric Pattern
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2023 Canadian Wildfires
The season takes off
•A historic, record-breaking Canadian
wildfire season got off to a fast start.
•Wildfire activity exploded in May, driven
by anomalous atmospheric pattern
•Some fires would remain problematic for
months to come due to their location in
rugged terrain
•Prodigious amount of smoke across all
of Canada in June.
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2023 Canadian Wildfires
A cool June pattern leads to air quality trouble
•Anomalous June pattern that
featured strong northerly
transport of Canadian air led to
well-below normal
temperatures across the eastern
U.S.
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2023 Canadian Wildfires
A cool June pattern leads to air quality trouble
•Anomalous June pattern that
featured strong northerly
transport of Canadian air led to
well-below normal
temperatures across the eastern
U.S.
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2023 Canadian Wildfires
A cool June pattern leads to air quality trouble
•Unfortunately, this simultaneously
led to the intrusion of heavy
Canadian wildfire smoke into the
eastern U.S., including North
Carolina.
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Design values at the Remount (Mecklenburg County) and Lexington (Davidson County) monitors are
above the revised annual PM2.5 NAAQS of 9.0 µg/m3
PM2.5 NAAQS Current Status
NC Department of Environmental Quality
“Unusual or naturally occurring events that can affect air quality but are not
reasonably controllable using techniques that tribal, state or local air agencies
may implement in order to attain and maintain the National Ambient Air Quality
Standards.”
•Wildfires
•Prescribed fires
•High wind dust events
•Stratospheric ozone intrusions
•Volcanic and seismic activity
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Exceptional EventsDefinition
The EE Rule allows for the exclusion of data influenced by exceptional events
from use in actions with regulatory significance:
40 CFR 50.14(b)(1)
“The Administrator shall exclude data from use in determinations of exceedances and
violations…where a State demonstrates to the Administrator's satisfaction that an exceptional
event caused a specific air pollution concentration at a particular air quality monitoring location
and otherwise satisfies the requirements of this section.”
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Exceptional EventsDefinition
NCDAQ must provide data and sound reasoning for each exceptional day,
and EPA reviews the specifics of each day using a tiered weight of evidence
approach. Some days require more evidence -- more on that later.
•Narrative conceptual model
•Clear causal relationship and historical data analysis
•Not reasonably controllable or preventable
•Natural event or human activity unlikely to recur
•Public notification / mitigation
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Exceptional EventsRequirements
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1.Retrieve daily average concentrations from EPA’s AQS for both monitors from 2021-
2023
2.Sort highest to lowest and focus on top 20 highest days as a starting point for analysis
3.Use archived meteorological data, AIR tool, media reports to assess what happened
on those days and identify days influenced by wildfires
4.Calculate a new '21-'23 design value by systematically excluding the highest 2023
Canadian wildfire-influenced days from the dataset
5.Would we be in attainment if we can exclude those days?
Exceptional EventsData Analysis
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•We identified 4 multi-day episodes (14 days total) in 2023 that impacted both
monitors and resulted in some of the highest daily average concentrations measured
during the three-year design value period
June
6 – 11
June
28 – July 1
July
17 – 18
Exceptional EventsData Analysis
June
17 – 18
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Exceptional EventsJuly 17 – 18, 2023 Example
•The most severe smoke transport event presented in our EE demo
•Smoke primarily sourced from northwestern Canada
•Featured anomalously strong upper high and low pressure centers
resulting in air mass stagnation in NW Canada and downwind smoke
transport into the U.S
•Smoke mixed down to the surface in NC after frontal passage
Source: National Park Service
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Exceptional EventsJuly 17 – 18, 2023 Example
Typical day: June 10, 2024 Smoky day: July 17, 2023
•Smoke (satellite detected)
wraps around anomalous
mid-level low as it moves
SE
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Exceptional EventsJuly 17 – 18, 2023 Example
•Anomalous high pressure over NW Canada
(red/orange area)
•Anomalous low pressure digging southward over
NE U.S. (purple/blue area)
NC Department of Environmental Quality
Exceptional EventsJuly 17 – 18, 2023 Example July 17
July 18
22 NC Department of Environmental Quality
Exceptional EventsJuly 17 – 18, 2023 Example
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•Quasi-stationary front in
Western NC on July 16;
smoke-laden airmass behind
front
•Front moves across NC on July
17; smoke aloft mixes down to
surface and impacts Lexington
and Remount monitors
•Front stalls again over Coastal
Plain on July 18; high pressure
behind front produces overnight
inversion and traps particle
pollution near surface
NC Department of Environmental Quality
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•Back trajectories show Code Orange PM2.5 observations on July 16 in KY/OH/IL, the
source region for the Lexington and Remount monitors on July 17
Exceptional EventsJuly 17 – 18, 2023 Example
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Exceptional EventsJuly 17 – 18, 2023 Example
Hourly observations
(black line) and
running daily
average (blue bars)
on July 17 and 18
Lexington
Remount
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Exceptional EventsJuly 17 – 18, 2023 Example
•Both days exceeded the daily PM2.5 standard of 35 µg/m3 at both monitors
•Daily averages were 200-400% higher than historical 5-year average on the given date
* The historical average is defined as the daily average PM2.5 concentration over the previous 5-year period (2018-2022) on the
given date (i.e., the past 5 June 6ths, the past 5 June 7ths, etc.).
** The EPA Tier Level determines the level of evidence required to establish a clear causal relationship in a wildland fire PM2.5
exceptional events demonstration and was determined using EPA’s Tiering Tool output. The threshold listed represents the
minimum daily average concentration (µg/m3) needed to meet the Tier level listed for that specific monitor and month.
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•NCDAQ utilized EPA’s PM2.5 Tiering Tool to determine the tiering thresholds for the Lexington
and Remount monitors for June and July
Exceptional EventsTiering
Example tiering graph for the Lexington
Monitor for June Exceptional Events
(showing daily average PM2.5 values)
•Tier 1 ≥ 25.35 µg/m3 (red circles)
•Tier 2 ≥ 16.9 µg/m3 but < 25.35
µg/m3 (yellow circles)
•Tier 3 < 16.9 µg/m3 (blue circles)
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Exceptional EventsTiering
•14 individual days were identified in our analysis, and those days were a mixture of
both Tier 1 and Tier 2 days. No Tier 3 days were included in the EE demo.
•Both Remount and Lexington had six Tier 1 days and seven Tier 2 days, although
the days were not always the same tier at each monitor.
•July 17–18 (from the previous example) are both Tier 1 days for both monitors
•For all Tier 1 days, we provided similar evidence as the July 17–18 example.
•For all Tier 2 days, we provided additional pieces of evidence…
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Exceptional EventsTier 2 Evidence Examples
•Hourly METAR (Meteorological
Aerodrome Report) from Concord
Regional Airport that show smoke or
haze was observed at the surface at
that time
•FU = fumée (French) or smoke
(English)
•HZ = haze
•Visibilities from nearby airports in
statute miles. Under 10 SM indicates
obscuration (such as smoke, dust,
haze, etc.)
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Exceptional EventsTier 2 Evidence Examples
•NAAPS Global Aerosol Model
•HRRR-NCEP Near Surface
Smoke Model
•Skew-t (observed radiosonde
soundings) to illustrate
inversions that trap pollutants
near surface
NC Department of Environmental Quality
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Exceptional EventsNot reasonably controllable or preventable
•40 CFR § 50.14 (a)(8)(vii) provides that “the Administrator shall not require a State to
provide case-specific justification to support the not reasonably controllable or
preventable criterion for emissions-generating activity that occurs outside of the
State's jurisdictional boundaries within which the concentration at issue was
monitored.”
•This was the case with the 2023 Canadian wildfires. No federal or North Carolina policy
or regulatory action could have prevented the fires or the resulting smoke to cross
international borders and enter the United States or North Carolina.
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Exceptional EventsNatural event or human activity unlikely to recur
•40 CFR § 50.1(n) defines a wildfire as “any fire started by an unplanned ignition
caused by lightning; volcanoes; other acts of nature; unauthorized activity; or
accidental, human-caused actions, or a prescribed fire that has developed into a
wildfire. A wildfire that predominantly occurs on wildland is a natural event.”
•The 2023 Canadian wildfires qualify as a “natural event” because they were
unplanned, mostly lightning-ignited fires predominantly on wildland.
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Exceptional EventsPublic Notification
NC Department of Environmental Quality
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•Initial Notification [40 CFR 50.14(c)(2)]
•Submitted to EPA Sept. 11, 2024, to propose days to include in EE demonstration
•EPA responded and agreed with initial notification proposal
•EE Demonstration [40 CFR 50.14(c)(3)]
•Draft EE demonstration prepared and revised to address EPA comments
Exceptional EventsDemonstration Review / Public Comment Process
NC Department of Environmental Quality
•Released for public comment
from Nov. 20 – Dec. 20, 2024
•DAQ is currently addressing
public comments received,
which will be included with
responses in the final EE Demo
submitted to EPA
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Nov 20 - Dec 20, 2024: NCDAQ’s 30-Day Public Comment Period on EE demo
NCDAQ addresses public comments
Feb 7, 2025: NCDAQ submits EE demo to EPA
Various steps including EPA notification to NCDAQ of intended modifications to designation recommendation, EPA’s 30-Day Public Comment Period, NCDAQ submits additional info to EPA re: any modifications
Feb 6, 2026:
EPA promulgates final 2024 PM2.5 NAAQS area designations
Timeline
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•North Carolina’s air quality is excellent overall and we’ve been in
attainment with all NAAQS since 2015
•Sometimes, events outside our control can impact air quality to such an
extent that it can skew the design value of a monitor
•NCDAQ can utilize the EE Rule to support our PM2.5 designation
recommendations (i.e., the 2023 Canadian wildfire smoke intrusions did
have significant regulatory implications)
Key Messages
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•NCDAQ is working closely with the EPA’s Region 4 team during this
process
•If concurred upon by EPA, this data would not be deleted from the record;
rather, it will be flagged so that it doesn’t “count against” us in regulatory
decisions
•NCDAQ has recommended statewide attainment for the revised 2024
PM2.5 NAAQS, supported by the requested exclusion of certain days
impacted by 2023 Canadian wildfire smoke
Key Messages
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Thank you! Questions?
Contact Info:
Sara Kreuser
Meteorologist
NCDEQ, Division of Air Quality
[e-mail]
Get the official AQ forecast and
past/present data here:
https://airquality.climate.ncsu.edu/
NC Department of Environmental Quality