Agenda Item III-1_Approved RIA

1
Regulatory Impact Analysis for Revisions to 15A NCAC 02D .0410
Rule Citation Number 15A NCAC 02D .0410
Rule Topic: PM2.5 NAAQS Revision
DEQ Division: Division of Air Quality
Agency Contact: Katherine Quinlan, Rule Development Branch Supervisor
Division of Air Quality (DAQ)
[phone]
[e-mail]
Analyst: Bradley Nelson, DAQ
[phone]
[e-mail]
Impact Summary: State government: No
Local government: No
Substantial impact: No
Private Sector: No
Authority: G.S. 143-215.3(a)(1); G.S. 143-215.107(a)(3)
Necessity: To revise the primary annual ambient air quality standard for particles with an
aerodynamic diameter less than or equal to a nominal 2.5 micrometers (PM2.5) in
15A NCAC 02D .0410 from 12.0 micrograms per cubic meter (µg/m3) to 9.0
µg/m3 to incorporate the United States (U.S.) Environmental Protection Agency
(EPA) revision to the primary annual PM2.5 National Ambient Air Quality
Standard (NAAQS) for PM2.5 effective May 6, 2024.

2

Contents
I. Background .......................................................................................................................................... 4
II. Reason for Rule Adoption .................................................................................................................... 5
III. Proposed Rules ..................................................................................................................................... 5
IV. Estimating the Fiscal Impacts .............................................................................................................. 5
V. Public Health and Environmental Impacts ......................................................................................... 10
VI. Cost and Benefit Summary ................................................................................................................ 11
VII. Rule Alternatives ................................................................................................................................ 11

3

Acronyms
Abbreviation Term
$ Dollars
% Percent
15A NCAC Title 15A of the North Carolina Administrative Code
40 CFR Title 40 of the Code of Federal Regulations
CO Carbon Monoxide
CAA Clean Air Act
DAQ Division of Air Quality
DEQ Department of Environmental Quality
EE Exceptional Events
EPA U.S. Environmental Protection Agency
FR Federal Register
I-SIP Infrastructure SIP
µg/m3
2
3
PM2.5

4

I. Background
The requirements in 15A NCAC 02D .0410, PM2.5 Particulate Matter, provide the primary annual and
24-hour ambient air quality standards for particles with an aerodynamic diameter less than or equal to a
nominal 2.5 micrometers (PM2.5) based on the National Ambient Air Quality Standards (NAAQS). The
PM2.5 NAAQS are set by the EPA to protect the public from the health impacts of fine particulate matter.
Sections 108 and 109 of the Clean Air Act (CAA) govern the establishment, review, and revision, as
appropriate, of the NAAQS. The EPA has set primary and secondary NAAQS for six pollutants that are
considered harmful to public health and the environment. These pollutants include carbon monoxide
(CO), lead (Pb), particulate matter (PM), ozone (O3), nitrogen dioxide (NO2), and sulfur dioxide (SO2).
The standard for PM includes both particles with an aerodynamic diameter less than or equal to a nominal
10 micrometers (PM10) and PM2.5. These primary standards are set at a level that protects public health
with “an adequate margin of safety” and the secondary standards are set at a level to protect the public
welfare from “any known or anticipated adverse effects.” Section 109(d) of the CAA requires the EPA to
review the standards every five years to ensure their adequacy. The CAA requires the EPA to base the
decisions for primary standards on health considerations only without consideration of economic factors.
The first primary ambient standards for PM2.5 were established by the EPA on July 18, 1997, at an annual
ambient concentration of 15 µg/m3 and a 24-hour concentration of 65 µg/m3 (62 Federal Register (FR)
38652).1 On October 17, 2006, the EPA reviewed the ambient air quality standards for PM2.5 and revised
the 24-hour standard to 35 µg/m3 while keeping the annual ambient standard at 15 µg/m3 (71 FR 61144). 2
On January 15, 2013, the EPA reviewed the ambient air quality standards for PM2.5 and revised the annual
ambient standard to 12.0 µg/m3 while retaining the 24-hour standard at 35 µg/m3 (78 FR 3086).3
On February 7, 2024, the EPA announced a revision to the primary ambient PM2.5 standard by
strengthening the annual concentration from 12.0 µg/m3 to 9.0 µg/m3; EPA is retaining the current
primary 24-hour PM2.5 standard at a level of 35 µg/m3. These changes are based on a reconsideration of
the December 18, 2020, final decision on the primary NAAQS for particulate matter. In that December
2020 final decision, the EPA retained the 2012 particulate matter standards without any revisions (85 FR
82684).4 In June 2021, the EPA announced its decision to reconsider the December 2020 decision
because the available scientific evidence and technical information indicated that the current standards
may not be adequate to protect public health and welfare, as required by the CAA.5 The reconsideration

1 U.S. EPA, National Ambient Air Quality Standards for Particulate Matter, 62 FR 38652, July 18, 1997.
https://www.govinfo.gov/content/pkg/FR-1997-07-18/pdf/97-18577.pdf
2 U.S. EPA, National Ambient Air Quality Standards for Particulate Matter, 71 FR 61144, October 17, 2006.
https://www.govinfo.gov/content/pkg/FR-2006-10-17/pdf/06-8477.pdf
3 U.S. EPA, National Ambient Air Quality Standards for Particulate Matter, 78 FR 3086, January 15, 2013.
https://www.govinfo.gov/content/pkg/FR-2013-01-15/pdf/2012-30946.pdf
4 U.S EPA, Review of the National Ambient Air Quality Standards for Particulate Matter, 85 FR 82684, December
18, 2020. https://www.govinfo.gov/content/pkg/FR-2020-12-18/pdf/2020-27125.pdf
5 EPA to Reexamine Health Standards for Harmful Soot that Previous Administration Left Unchanged, June 10,
2021, https://www.epa.gov/newsreleases/epa-reexamine-health-standards-harmful-soot-previous-administration-left-
unchanged

5

process concluded that the scientific evidence and information supported revising the level of the primary
annual PM2.5 standard to 9.0 µg/m3 while retaining the primary 24-hour PM2.5 standard at a level of
35 µg/m3. The revised annual standard was published in the FR on March 6, 2024, with an effective date
of May 6, 2024 (89 FR 16202).6
II. Reason for Rule Adoption
North Carolina codifies the EPA’s NAAQS in Title 15A of the North Carolina Administrative Code (15A
NCAC), Subchapter 02D, Section .0400, Ambient Air Quality Standards. Specifically, Rule 02D .0410
contains the annual and 24-hour NAAQS for PM2.5.
To reflect the EPA’s revision to the annual PM2.5 NAAQS, the DAQ is proposing to revise the primary
annual ambient air quality standard for PM2.5 in 15A NCAC 02D .0410 to reflect the revised PM2.5 annual
NAAQS of 9.0 µg/m3.
III. Proposed Rules
The DAQ is proposing amendment to the following rule:
15A NCAC 02D .0410, PM2.5 Particulate Matter
This Rule is proposed for amendment to update the primary annual ambient standard for PM2.5 from
12.0 µg/m3 to 9.0 µg/m3.
IV. Estimating the Fiscal Impacts
This rulemaking proposes to reflect a federal regulation that the agency is required to adopt. The EPA’s
strengthened primary annual PM2.5 NAAQS value becomes effective on May 6, 2024, and is required to
be implemented by states and regulated entities upon this date. Therefore, the effects described below on
the state and regulated entities are directly attributable to EPA’s action, not the DAQ’s proposed
incorporation of EPA’s revised NAAQS into 15A NCAC 02D .0410. For context, this section provides an
overview of key items that impact the DAQ and discusses uncertainties associated with air quality
permitting impacts on industries. For the State, the key impacts include following a process for
designating the State’s attainment status for specific geographic areas with respect to the revised NAAQS
and preparing a State Implementation Plan (SIP) referred to as an “Infrastructure SIP” (I-SIP). In
addition, this section also summarizes information from EPA’s regulatory impact analysis (RIA) for the
final rule revising the PM2.5 NAAQS.
Designation Process
Consistent with the schedule in CAA section 107(d)(1), the EPA’s promulgation of a new or revised
NAAQS starts a 2-year process for designating geographic areas of the state as either “attainment,”

6 U.S. EPA, Reconsideration of the National Ambient Air Quality Standards for Particulate Matter, 89 FR 16202,
March 6, 2024. https://www.govinfo.gov/content/pkg/FR-2024-03-06/pdf/2024-02637.pdf

6

“nonattainment,” or “unclassifiable.” Table 1 provides the anticipated schedule of milestones and
milestone dates for completing the designation process for the revised PM2.5 NAAQS.
Table 1. Anticipated Timeline for 2024 Revised Primary Annual PM2.5 NAAQS Initial Area
Designations Process*
EPA promulgates 2024 Revised Primary Annual PM2.5 NAAQS final rule February 7, 2024
2023 Design Values Available June 2024
demonstration supporting initial area designations No later than January 1, 2025
State submits (on behalf of the Governor) recommendations for PM2.5 designations and EE demonstration to EPA No later than February 7, 2025
2024 Design Values Available June 2025
EPA notifies North Carolina concerning any intended modifications to their recommendations (120-day letter) No later than October 9, 2025 (120 days prior to final PM2.5 area designations)
recommendations and EPA’s intended modifications, if any, and Mid-October 2025
End of 30-day public comment period Mid-November 2025
State submits additional information, if any, to respond to EPA’s
modification of recommended designations
the publication of the notice of availability
of State recommendations and EPA’s
EPA promulgates final 2024 PM2.5 NAAQS area designations February 6, 2026
* This table reflects EPA’s anticipated designations timeline. Some dates may shift as the process moves forward.
A State must submit its initial designation recommendations to the EPA for the revised PM2.5 NAAQS by
February 7, 2025 (i.e., no later than 1 year following promulgation of the revised NAAQS). The DAQ
will follow EPA’s guidance in preparing its designation recommendations.7 A State’s recommendations
must be based on the design value calculated using the three most recent years of certified monitoring
data (i.e., 2021-2023) measured by an air quality monitor sited and operated in accordance with federal
reference methods (or equivalent methods) for tracking compliance with the NAAQS.8 Based upon these
monitoring data (as well as the emissions and emissions-related data, meteorology, geography/topography
and jurisdictional boundaries) the DAQ will develop recommendations to identify areas as attainment,

7 EPA Memorandum form Joseph Goffman, Assistant Administrator, to Regional Administrators, Regions 1-10,
"Initial Area Designations for the 2024 Revised Primary Annual Fine Particle National Ambient Air Quality
Standard," February 7, 2024, https://www.epa.gov/system/files/documents/2024-02/pm-naaqs-designations-
memo_2.7.2024-_-jg-signed.pdf
8 A design value is a statistic that describes the air quality status of a given air quality monitor relative to the level of
the NAAQS. Design values are defined to be consistent with the individual NAAQS as described in Title 40 of the
Code of Federal Regulations (40 CFR), Part 50. The design value for the primary PM2.5 NAAQS is the 3-year average of the of PM2.5 annual mean mass concentrations that is compared to the NAAQS to determine compliance. If the design value for a monitor is ≤9.04 ug/m3, the monitor in attainment with the standard. If the design value for a monitor is >9.04 ug/m3, the monitor is in violation of the standard.

7

nonattainment, or unclassifiable. The DAQ anticipates requesting township level designation due to
potential implications for the Prevention of Significant Deterioration (PSD) permitting program of having
an entire county designated as a single area rather than smaller areas (e.g., partial counties).
North Carolina operates 18 PM2.5 regulatory air quality monitors across the state to track compliance with
the PM2.5 standards. Based on the certified monitoring data from 2020-2022, all areas of North Carolina
would have been meeting the new annual PM2.5 standard (9.0 µg/m3) during this time. Preliminary air
quality monitoring data from 2023, still undergoing quality assurance review, indicates that most
monitoring sites in North Carolina are meeting the new standard. However, the preliminary 2023 data
shows that four monitoring sites in the state may be slightly above the new standard, due to influences of
Canadian wildfire smoke. These sites, as shown in Figure 1, are in Mecklenburg, Wake, Forsyth, and
Davidson Counties. Without the influence from Canadian wildfire smoke, none of North Carolina's
monitors would have exceeded the new standard in 2023. It is important to note that Teledyne PM2.5
monitors are used at the Forsyth County and Wake County sites. The EPA will be applying a correction
algorithm to the Teledyne monitoring data for all sites in the U.S. prior to certifying the data. As a result,
the design value for these sites may show compliance with the revised PM2.5 NAAQS after applying the
correction algorithm.
The EPA has said it will consider impacts from wildfire smoke when making designations if the State
submits an exceptional events (EE) demonstration for the dates impacted by wildfire smoke for all
affected monitors. The EPA’s EE rule establishes criteria and procedures for use in determining if air
quality monitoring data has been influenced by EE such as wildfire smoke and fireworks.9 The DAQ is
reviewing its monitoring data from 2023 in preparation for preparing and submitting an EE demonstration
to EPA for monitoring sites above 9.04 µg/m3.
Final designations will be based on PM2.5 monitoring data collected from 2022-2024. Until these data are
collected and reviewed, it is too early to know which, if any, areas of North Carolina may be in
nonattainment with the new standard. As with all the NAAQS, it is DAQ’s priority to evaluate PM2.5
levels daily and identify and address elevated levels caused by anthropogenic sources to maintain
statewide attainment with the revised PM2.5 NAAQS and receiving a statewide designation of attainment
by EPA in February 2026.

9 Treatment of Data Influenced by Exceptional Events, Final Rule, 81 FR 68216, October 3, 2016,
https://www.govinfo.gov/content/pkg/FR-2016-10-03/pdf/2016-22983.pdf

8

Figure 1. North Carolina PM2.5 Preliminary Annual Design Values (2021-2023) (Based on certified data for 2021 and 2022 and preliminary data from 2023 which is still undergoing DAQ quality assurance review)
Infrastructure SIP (I-SIP)
CAA Title I (Air Pollution Prevention and Control), Section 110(a) requires a State to prepare a SIP for
submittal to EPA for approval that documents the State's infrastructure (authority, rules,
programs/policies) to implement, maintain, and enforce compliance with a new or revised primary and/or
secondary NAAQS. CAA Section 110(a)(1) requires a State to submit this SIP to EPA within 3 years
from promulgation of the revised or new NAAQS. CAA Section 110(k)(1) directs EPA to determine if a
SIP is complete within 60 days of submission, but no later than 6 months after the submission date. CAA
Section 110(k)(2) directs EPA to take final action on a SIP submission within 1 year after the submission
is determined to be complete. Section 110(a)(2) specifies the substantive elements that a State’s I-SIP
must address to receive EPA’s approval. It includes requirements of various air programs, resources, and
authority to be in place such as an ambient air quality monitoring network and data systems, programs for
enforcement of control measures, and adequate authority and resources to implement the plan.
The DAQ will prepare an I-SIP for the revised PM2.5 NAAQS for submittal to EPA (after public notice
and comment) by February 5, 2027. The I-SIP will need to be issued for a 30-day comment period and
revised to address any comments prior to submittal to EPA. The I-SIP must address each of the following
12 CAA elements:
• Section 110(a)(2)(A) - Enforceable Emission Limitations and Other Control Measures
• Section 110(a)(2)(B) - Air Quality Monitoring, Compilation, Data Analysis, and Reporting
• Section 110(a)(2)(C) - Enforcement and Stationary Source Permitting
• Section 110(a)(2)(D) - Interstate Transport
• Section 110(a)(2)(E) - Resources, Conflict of Interest, and Emergency Backstop
• Section 110(a)(2)(F) - Stationary Source Emissions Monitoring, Data Collection, and Reporting
• Section 110(a)(2)(G) - Emergency Powers and Contingency Plans

9

• Section 110(a)(2)(H) - SIP Revision for Revised Air Quality Standards or New Attainment Methods
• Section 110(a)(2)(J) - Consultation and Public Notification
• Section 110(a)(2)(K) - Air Quality Modeling and Reporting
• Section 110(a)(2)(L) - Major Stationary Source Permitting Fees
• Section 110(a)(2)(M) - Consultation with Local Entities
Note that the Section 110(a)(2)(D) (Interstate Transport) element (often referred to as the “Good Neighbor” SIP) typically is supported by air quality modeling to determine an upwind State’s PM2.5
concentration contributions to downwind State maintenance and nonattainment monitors. The DAQ anticipates that EPA will be issuing future guidance to states for preparing their Good Neighbor SIPs and depending on EPA’s schedule, this CAA element may be addressed in a SIP that is separate from the I-SIP.
EPA’s Regulatory Impact Analysis
In their reconsideration of the 2020 Particulate Matter NAAQS final action, the EPA found that the
current primary annual PM2.5 standard may not be adequate to protect public health and welfare with an
adequate margin of safety. Therefore, the EPA revised the existing annual standard from the current level
of 12.0 µg/m3 to 9.0 µg/m3. Even though economic factors were not considered in the EPA’s
determination of the revised NAAQS value, an RIA was developed by the EPA as part of the
reconsideration package.
The fiscal impacts noted in this analysis are based on the impacts estimated by the EPA in their RIA for
the reconsideration package.10 The analyses were performed for the U.S. in four regions (northeast,
southeast, west, and California), and the EPA analyzed the final revised annual and current 24-hour
standard levels of 9 µg/m3 and 35 µg/m3, respectively, as well as three alternative standard levels (for the
annual and/or 24-hour standards).11 Within each region, the RIA identifies counties that may exceed the
annual or 24-hour standard for each scenario. Table 4A-3 of the EPA’s RIA provides the estimated annual
control costs for the four scenarios (proposed standards plus three alternatives). Control costs were
estimated using the EPA’s estimated 2032 design values for counties identified as possibly exceeding the
standards of each scenario and calculating annual costs from application of control technology by
industries located in the county to attain the new standard. In the southeast region, the EPA identified
Forsyth and Mecklenburg Counties as the potential counties in North Carolina that may exceed one or
both of the standard levels in at least one of the scenarios.12 However, for the scenario of the proposed

10 U.S. EPA, Final Regulatory Impact Analysis for the Reconsideration of the National Ambient Air Quality
Standards for Particulate Matter, January 2024. EPA-452/R-24-006.
https://www.epa.gov/system/files/documents/2024-02/naaqs_pm_reconsideration_ria_final.pdf
11 The four scenarios analyzed by the EPA in their RIA were: 1) the final revised annual standard (9 µg/m3) in
combination with the current 24-hour standard (35 µg/m3) that is being retained by the EPA; 2) a less stringent
alternative annual standard level of 10 µg/m3 in combination with the current 24-hour standard (i.e., 10/35 µg/m3);
3) a more stringent alternative annual standard level of 8 µg/m3 in combination with the current 24-hour standard
(i.e., 8/35 µg/m3); and 4) a more stringent alternative 24-hour standard level of 30 µg/m3 in combination with an
annual standard level of 10 µg/m3 (i.e., 10/30 µg/m3).
12 Table 4A-3 of EPA’s RIA presents the results for each of these four scenarios, but NC DAQ has only summarized
the results presented for the values in EPA’s final rule, which are being incorporated into Rule 02D .0410 in this
action.

10

standard (i.e., annual 9.0 µg/m3, 24-hour 35 µg/m3), Table 4A-3 of EPA’s RIA lists annual control costs
of $0 million of 2017 dollars (2017$) for Forsyth County and $0 million of 2017$ for Mecklenburg
County. Table 4A-3 of the EPA’s RIA only identifies control costs for Forsyth County and Mecklenburg
County for the alternative scenario of an annual standard of 8 µg/m3 in combination with a 24-hour
standard of 35 µg/m3. No other counties in North Carolina were identified as exceeding the proposed
standard or two other alternatives in 2032 in the EPA’s RIA.
Uncertainties
An uncertainty that cannot be quantified is the impact on facilities’ decisions for new construction or
expansion projects in relation to the revised standard. Reducing the PM2.5 NAAQS to a level closer to
current measured ambient background concentrations may result in fewer new industrial constructions
and/or plant expansions if facilities are unable to demonstrate that their project will not cause or
contribute to an exceedance of the revised PM2.5 NAAQS, which is a critical piece of the permitting
process. Prior to applying for a new permit or permit modification, facilities often evaluate the impacts of
their project (which may involve air dispersion modeling or other types of analyses) to determine if the
project is viable. Because this evaluation occurs at the facility during the planning stage, the DAQ will
not be aware of these activities and therefore cannot estimate the impacts associated with projects that do
not move forward as a result of not being able to demonstrate compliance with the PM2.5 NAAQS.
V. Public Health and Environmental Impacts
The public health and environmental impacts associated with the DAQ’s proposed change to the primary
annual PM2.5 NAAQS concentration are attributable to EPA’s rule. In the EPA’s reconsideration of the
primary ambient annual standard for PM2.5, they found that the newly available data supports a causal
relationship between long-term exposures and respiratory effects, nervous system effects, and cancer.
This section discusses the health benefits provided in EPA’s RIA for the revised PM2.5 NAAQS.
Benefits from PM2.5 Emission Reductions
The health benefits from the reduction of PM10 and PM2.5 are numerous. Small particles pose the greatest
risk because they can get deep in your lungs and even get into your bloodstream. Numerous scientific
studies have linked particle pollution exposure to a variety of problems, including: premature death in
people with heart or lung disease; nonfatal heart attacks; irregular heartbeat; aggravated asthma;
decreased lung function; and increased respiratory symptoms, such as irritation of the airways, coughing
or difficulty breathing. People with heart or lung diseases, children, and older adults are the most likely to
be affected by particle pollution exposure.
PM also has environmental effects including: making lakes and streams acidic; changing the nutrient
balance in coastal waters and large river basins; depleting the nutrients in soil; damaging sensitive forests
and farm crops; affecting the diversity of ecosystems; and contributing to acid rain effects. PM can also
cause damage to materials such as statutes and monuments.
The EPA did not provide State-specific benefits in their RIA, but instead estimated benefits by region.
The EPA’s analysis included North Carolina in the southeast region, which also includes Virginia, South
Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, Arkansas, Kansas, Oklahoma, and Texas. In

11

Table 5-9 of their RIA, the EPA estimated $5.3 billion (in 2017$) of health benefits for the southeast
region. The EPA estimated those benefits by calculating the amount of PM2.5 emission reductions that
would be needed in nonattainment areas, for those areas to reach attainment in 2032. In addition, the EPA
noted that there are unquantified health and welfare benefits that are not included in the total. Most of
these benefits will occur as a result of reductions needed in seven counties in the southeast region,
including four counties in Texas, one county in Louisiana, one county in Georgia, and one county in
Florida. Since the EPA’s analysis only provides a singular value of health benefits across the twelve
southeast states, the DAQ is unable to refine these regional health benefits to the state- or county-level.
Further, it should be noted that EPA’s benefits analysis focused on the health benefits directly associated
with the amount of emission reductions that nonattainment areas would need to achieve to attain the
proposed or alternative standards evaluated. However, there are additional benefits associated with
continued attainment of the annual standard, such as the avoidance of future adverse health impacts
associated with chronic exposure to PM2.5. Additionally, EPA establishes limits on the amount of
pollution that an attainment area can increase. Known as “PSD increments”, these limits prevent the air
quality in clean areas from deteriorating to the level set by the NAAQS.13
VI. Cost and Benefit Summary
As described in the sections above, any costs or benefits associated with implementation of this revised
standard in North Carolina will not be the result of its incorporation into the NC Administrative Code.
Rather, any costs or benefits associated with the revised standard will be attributable to EPA’s action
which requires implementation by the states beginning May 6, 2024. The EPA estimated no annual
control costs to North Carolina associated with the revised standard. Benefits of the change to the primary
annual standard were estimated to be $5.3 billion (in 2017$) of health benefits for the southeast region,
which includes North Carolina.
VII. Rule Alternatives
In accordance with N.C.G.S. 150B-21.4(b2)(5), the RIA for a proposed rulemaking with a substantial
economic impact is required to contain a description of at least two alternatives to the proposed rules. As
defined in N.C.G.S. 150B-21.4(b1), “substantial economic impact” means an aggregate financial impact
on all persons affected of at least one million dollars ($1,000,000) in a 12-month period. The proposed
rule revision does not result in any impacts; therefore, it will not have a substantial economic impact, and
an evaluation of alternatives is not required for this fiscal analysis. In addition, because this is a federal
regulation that the agency is required to adopt, there would not be any viable alternatives to consider.

13 U.S. EPA, Prevention of Significant Deterioration Basic Information. Retrieved on April 23, 2024 from epa.gov:
https://www.epa.gov/nsr/prevention-significant-deterioration-basic-information
1 of 1
15A NCAC 02D .0410 is proposed for amendment as follows: 1
2
15A NCAC 02D .0410 PM2.5 PARTICULATE MATTER 3
(a) The national primary ambient air quality standards for PM2.5 shall be 12.0 9.0 micrograms per cubic meter (µg/m3) 4
annual arithmetic mean concentration and 35 µg/m3 24-hour average concentration measured in the ambient air as 5
PM2.5 (particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers) by either: 6
(1) A reference method based on appendix L to 40 CFR Part 50 and designated in accordance with 40 7
CFR Part 53; or 8
(2) An equivalent method designated in accordance with 40 CFR Part 53. 9
(b) The primary annual PM2.5 standard shall be deemed met when the annual arithmetic mean concentration, as 10
determined in accordance with Appendix N of 40 CFR Part 50, is less than or equal to 12.0 9.0 µg/m3. 11
(c) The primary 24-hour PM2.5 standard shall be deemed met when the 98th percentile 24-hour concentration, as 12
determined in accordance with Appendix N of 40 CFR Part 50, is less than or equal to 35 µg/m3. 13
14
History Note: Authority G.S. 143-215.3(a)(1); 143-215.107(a)(3); 15
Eff. April 1, 1999; 16
Amended Eff. September 1, 2015; January 1, 2010; 17
Readopted Eff. January 1, 2018. 2018; 18
Amended Eff. 19
20