The Revised PM2.5 NAAQS and What It Means for Your Facility

On February 7, 2024, the U.S. Environmental Protection Agency (EPA) lowered the annual primary National Ambient Air Quality Standard (NAAQS or the standard) for fine particulate matter from 12.0 to 9.0 micrograms per cubic meter (ug/m3). Fine particulate matter is otherwise known as particulate matter with an aerodynamic diameter of less than or equal to 2.5 microns (PM2.5). The revised standard will officially become effective 60 days after February 7th (April 7, 2024).

The EPA also indicated they will revise the Significant Impact Level (SIL) for annual PM2.5. This impacts any facility conducting dispersion modeling. The EPA will lower the current SIL of 0.3 ug/m3—but to what level has not yet been determined.

The EPA did not change the existing NAAQS for 24 hour PM2.5 or for coarse PM, which is also known as particulate matter with an aerodynamic diameter of less than or equal to 10 microns (PM10).

Along with the announcement, the EPA published a trove of information related to the process and expected timeline for implementing the revised standard. At first glance, the timeline appears to move at a glacial pace:

• Within two years (2026) the EPA will designate all airsheds as either being in attainment, in nonattainment, or being unclassifiable with respect to the revised NAAQS.
• A year later (2027) all states must submit an infrastructure State Implementation Plan (SIP) indicating how they will comply with the NAAQS.
• Eight years later (2032) airsheds designated as being in nonattainment must demonstrate compliance with the lowered NAAQS.

In practice, this pace will not feel glacial at all.

For those currently planning projects or undertaking permit modifications at their facilities, it’s prudent to think of the revised NAAQS as already being in effect. For projects with permit applications, including dispersion modeling analyses that are currently under review, regulatory agencies have the discretion to request that those applications be revised to show that they meet the lower standard. Like others in the environmental permitting world, we are anxiously awaiting official word from state and local regulatory agencies indicating how they intend to proceed.

As part of the information provided in their announcement, EPA provided a list of 52 counties throughout the United States that, as of 2023, would not meet the revised standard. This list is derived from air quality monitoring data collected between 2020 and 2022. The final determination will come from monitoring data collected between 2022 and 2024, but the list does provide insight into the locations that will be scrutinized by state regulators as they develop their SIPs that ensure their airsheds are able to comply with the lowered NAAQS.

For those who have facilities in one of the 52 listed counties, there will not be an immediate change to the airshed’s attainment status. However, planned projects and operations with the potential to emit particulates should be reviewed through the lens that additional controls and/or emissions mitigation strategies may be necessary to comply with the lower standard.

Regardless of whether a facility is considered a major, minor, synthetic minor, or area source, all facilities should review their air quality permits for sources of particulate matter (not just PM2.5) and consider the potential impacts of the revised NAAQS on their current and future operations.