4 The record articles

U.S. EPA to Reconsider PM2.5 NAAQS

Posted: July 23rd, 2021

Authors: Dan D. 

On June 10, 2021 U.S. EPA announced that it would reconsider the previous administration’s decision to retain the particulate matter less than 2.5 microns (PM2.5) National Ambient Air Quality Standard (NAAQS).  The previous administration made its final decision to retain both the annual and 24-hour PM2.5 NAAQS even though U.S. EPA’s 2019 Integrated Science Assessment (ISA) concluded that there was scientific evidence that supported lowering the annual PM2.5 NAAQS.  The current annual PM2.5 NAAQS is 12 micrograms per cubic meter (µg/m3) and was last lowered from 15 µg/m3 to 12 µg/m3 in 2012.  The 24-hour PM2.5 NAAQS is 35 µg/m3 and hasn’t been changed since initially being established in 2006.

The Clean Air Act (CAA) requires U.S. EPA to re-evaluate the NAAQS every 5 years.  The process involves the development of an ISA which evaluates peer-reviewed literature published since the last assessment on the health and welfare effects of the NAAQS under review and the development of a Risk/Exposure Assessment (REA).  The Clean Air Scientific Advisory Committee (CASAC) then provides an independent review of both the ISA and REA.  Finally, a Policy Assessment (PA) is developed by U.S. EPA which considers both the ISA, REA, and policy implications and makes a recommendation on whether to retain or revise the NAAQS.  The 2019 particulate matter (PM) ISA included recommendations for lower of the annual PM2.5 NAAQS to between 8 and 10 µg/m3, although the final PA concluded that there was not enough evidence to support lowering the annual PM2.5 NAAQS.

As part of the reconsideration, U.S. EPA intends to develop a supplement to the 2019 PM ISA that will consider the most up-to-date science.  This approach means that the NAAQS review process will not be restarted and as a result U.S. EPA expects to finalize a proposal to retain or lower the PM2.5 NAAQS by Summer of 2022, following up with a final rule by Spring of 2023.

How Would a Reduced PM2.5 NAAQS Impact My Facility?

The current measured annual PM2.5 concentration average across all state operated ambient monitors in the country is 7.8 µg/m3 for the 2018-2020 time period.  As a result, there is little “headroom” available below the current annual PM2.5 NAAQS of 12 µg/m3 for new projects and facilities or for areas to remain in attainment with the NAAQS.  There are two critical ways that lowering the PM2.5 NAAQS could impact your facility.  First, for projects that trigger Prevention of Significant Deterioration (PSD) permitting air quality modeling requirements, the available headroom could shrink from already very restrictive levels to a level that would make it nearly impossible to model below the PM2.5 annual NAAQS for even the smallest increases in PM2.5 emissions.  Second, due to current monitored concentration levels many areas across the country could see newly established nonattainment areas.  If your facility is located in a newly established PM2.5 nonattainment area, nonattainment new source review (NNSR) permitting would be required instead of PSD permitting.  While the air quality modeling is not required as a part of NNSR permitting, Lowest Achievable Emissions Rate (LAER) is required instead of Best Avaiable Control Technology (BACT).  The main difference between BACT and LAER is the removal of the economic consideration (i.e., if means to reduce emissions are technically feasible, they are required no matter the cost).  In addition, Emissions Reductions Credits (ERCs) are required to be purchased to offset emissions increases as part of the NNSR permitting program.  ERCs can be difficult to procure and expensive in some situations.  This adds cost and can delay implementation of a project.  Additionally, states that have newly designated nonattainment areas are required to develop a State Implementation Plan (SIP) to bring the area back into attainment with the NAAQS.  This process could require your facility to install control equipment or otherwise take new, more restrictive permit limits even if your facility is not currently engaged in an air permitting project.  This could even occur if your facility is not the one that is primarily responsible for the creation of the nonattainment area in the first place.

CLEAN Future Act Implications

While not directly tied into the reconsideration of the annual PM2.5 NAAQS, one piece of draft legislation that is out there related to the new administration’s focus on Environmental Justice is the CLEAN Future Act.  One of the two criteria that would determine whether a census tract would be considered overburdened for the purpose of the law would be “Has been determined to have an annual mean concentration of PM2.5 of greater than 8 µg/m3, as determined over the most recent 3-year period for which data are available”.  As discussed above, the national annual-average PM2.5 concentration is 7.8 µg/m3.  This means that if the Clean Future Act passes as currently proposed, nearly half of the United States would be considered overburdened not even considering the other criteria in the law, that being a cancer risk of greater than 100 in 1,000,000.  The implications of your facility being in such an area would be significant:

  • After the date of enactment of the CLEAN Future Act, no permit shall be granted by a permitting authority for a proposed major source that would be in an overburdened census tract.
  • After January 1, 2025, no permit for a major source in an overburdened census tract shall be renewed.

Thus, regardless of whether or not the annual PM2.5 NAAQS is revised, should the CLEAN Future Act pass, no permit action that triggered New Source Review (NSR) permitting would be allowed in an area with an ambient annual PM2.5 concentration over 8 µg/m3, and existing major stationary sources in such areas could not renew their permits starting in 2025!

The Good News

You’ve still got time on your side if you start soon to complete and obtain a permit under the existing PM2.5 annual NAAQS and before any version of the CLEAN Future Act is finalized.  If you’re considering a project that could increase PM2.5 emissions from your facility that could trigger PM2.5 air quality modeling, now is the time to evaluate that project.  PSD permitting (typically the longest permitting program) is typically a 12-18 month process from application development to receipt of a final permit from the agency.  This would put your permit in hand before any potential revision of the PM2.5 NAAQS.  Once a permit has been finalized you have been grandfathered into the regulations promulgated at that time.  As long as you don’t need to make any additional changes to your permit you wouldn’t have to re-evaluate your project under any potential reduced PM2.5 NAAQS.  While the PSD permitting program is the Federal program that impacts most major facilities across the country be aware that the same recommendations can be made for states that have air quality modeling requirements for minor modifications or minor facilities that don’t trigger Major PSD permitting, as states that do require modeling for minor source projects typically use the current NAAQS as the thresholds for demonstrating compliance.

If you have any questions about a potential project that includes PM2.5 emissions or want to see how close your area’s ambient PM2.5 concentration is to the current PM2.5 NAAQS is, please contact Dan Dix at ddix@all4inc.com or at 610.422.1118.


    Sign up to receive 4 THE RECORD articles here. You'll get timely articles on current environmental, health, and safety regulatory topics as well as updates on webinars and training events.
    First Name: *
    Last Name: *
    Location: *
    Email: *

    Air and Water Virtual Conference - September 27-28Learn More