Regulation update: EPA announces final National Ambient Air Quality Standards (NAAQS) rule

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March 6, 2024 - As announced on February 7, 2024, the US Environmental Protection Agency (EPA) is lowering the primary annual National Ambient Air Quality Standard (NAAQS) for fine particulates (PM_2.5) from 12 to 9 micrograms per cubic meter (µg/m³). The final rule was published in today’s Federal Register, which sets the effective date of the revised standard to May 6, 2024 (60 days after publication).

Let’s explore the major impacts of the revised PM_2.5 standard.

Nonattainment and attainment areas

Lowering the annual PM_2.5 standard will have implications for:

Nonattainment areas: companies located in areas that will not meet the revised standard. The permitting requirements are more stringent and costly to implement compared to attainment areas. States will need to implement plan requirements that, among other items, include:
Control strategies.
Policies regarding PM₅ precursor pollutants.
Reasonable further progress requirements.
Attainment or unclassifiable areas: companies located in areas that will meet the revised standard. The most significant impact is greater challenges in the permitting process for new and modified major sources.

PSD permitting implications

Within 60 days of the final rule being effective, Prevention of Significant Deterioration (PSD) permitting using the revised PM_2.5 standard will apply to new major sources and modifications without final permits. This requires all applicants to conduct an air quality analysis considering the revised PM_2.5 NAAQS. Other impacts include the following:

Only applicants receiving final permits before the effective date avoid adjustments.
The PSD program will continue applying to major sources in attainment areas until the EPA completes new designations, which could take up to two years.
Applicants without final permits by the effective date must show that their source won't cause or contribute to a violation. The lower standard may provide challenges as background levels are close to the new standard, making modeling difficult.
The EPA is updating its Significant Impact Level (SIL) guidance for PM₅. A lower SIL is likely given the lower standard. This will make demonstrating insignificant impacts more difficult and expand Significant Impact Areas needing refined modeling.

Initial area designation

Within two years of the effective date, the EPA will designate all areas as attainment (meeting standards), nonattainment (not meeting standards), or unclassifiable (insufficient data to make a determination).
Nonattainment areas include:
Areas with ambient air quality monitors that have design values exceeding the standards.
Other nearby areas with sources of emissions contributing to the exceedance.
For annual PM₅, the design value for a monitor station is the annual arithmetic mean concentration of the most recent three years of quality-assured, certified air quality data.
In addition to air quality data, designations also consider emissions data, meteorology, geography/topography, and jurisdictional boundaries.
The EPA identified 120 counties with 2022 design value concentrations exceeding the revised standard. However, this is likely an underestimate due to COVID-19 impacts limiting data completeness for some sites.
More counties will likely exceed the standard as 2023 and 2024 air quality data is validated. For example, the EPA identified four exceeding counties in Ohio for 2022, but most Ohio monitors increased from 2022 to 2023, indicating that more counties will exceed with the 2023 data.

Nonattainment area impacts

In approximately two years, the nonattainment New Source Review (NSR) permitting program will apply to the construction of new major sources or sources making a major modification in the nonattainment areas for the revised PM_2.5 standard. Nonattainment NSR will require:

The application of Strict PM₅ emissions limits through installation of controls or operational limitations that produce the lowest achievable emission rate (LAER) and emission offsets. Offsets are emission reductions, generally obtained from existing sources located in the vicinity of a proposed source, which must offset the emissions increase from the new source or modification and provide a net air quality benefit.
Implementation of additional control strategies (such as reasonably available control measures and reasonably available control technology for direct PM₅ and relevant precursors) for existing major sources located in the newly designated PM_2.5 nonattainment areas.

The substantially lowered PM_2.5 standard will have widespread impacts, presenting new hurdles for companies and agencies alike.

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