4 The record articles

PM2.5 NAAQS Reconsideration Progress Update

Posted: March 31st, 2022

Authors: Dan D. 

As I discussed in my July 2021 blog post and my January 2022 Look Ahead article, the United States Environmental Protection Agency (U.S. EPA) is currently going through the process of reconsidering the previous administration’s decision to retain the particulate matter with a diameter less than 2.5 microns (PM2.5) National Ambient Air Quality Standards (NAAQS).  Since the January 2022 look ahead, three public meetings of the Chartered Clean Air Scientific Advisory Committee (CASAC) and CASAC Particulate Matter (PM) Panel (Panel) were held in late February and early March to discuss the draft CASAC reports on U.S. EPA’s “Supplement to the 2019 Integrated Science Assessment (ISA) for Particulate Matter” (Draft Supplement) and the draft “PM Policy Assessment.”  During the public meetings oral and written public comments were taken and deliberations among the Panelists were conducted.  During the last public meeting on March 4, 2022, the Chartered CASAC approved U.S. EPA’s draft “PM Policy Assessment.”

The CASAC-approved “PM Policy Assessment” concludes that the current primary annual PM2.5 NAAQS does not adequately protect public health and finds based on epidemiologic studies conducted in the United States that that an annual average standard in the range of 8-10 micrograms PM2.5 per cubic meter (µg/m3) would be appropriate.  All CASAC members agreed that the form and averaging time of the standard should be retained without revision.  A minority of CASAC members found that a range of 10-11 µg/m3 would be appropriate.  This determination almost guarantees that the current PM2.5 annual NAAQS of 12 µg/m3 will be lowered.  In addition, the CASAC-approved “PM Policy Assessment” also concludes that the current primary 24-hour PM2.5 NAAQS (35 µg/m3) does not adequately protect public health and should be lowered to a range of 25-30 µg/m3 to be adequately protective.  A minority of CASAC members concurred with U.S. EPA’s preliminary conclusion to retain the current 24-hour PM2.5 NAAQS without revision.  Based on this determination the 24-hour PM2.5 NAAQS will likely be lowered but this is less certain than in the case of the annual PM2.5 NAAQS.  In addition, it should be noted that some CASAC members also recommended that future studies consider shot-term exposure (shorter than 24 hours) in order to account for conditions that exist during wintertime stagnation and/or during heavy use of home woodstove heating, possibly setting the stage for a future 1-hour standard similar to the sulfur dioxide (SO2) and nitrogen dioxide (NO2) NAAQS.  Based on these proceedings U.S. EPA is one step closer to moving forward with lowering the PM2.5 NAAQS.

The next step in the PM2.5 NAAQS reconsideration process is for U.S. EPA to take CASAC and public comments into consideration and develop draft rulemaking for a proposed revised PM2.5 NAAQS.  This rulemaking is expected in Summer of 2022 following up with a final rule by Spring of 2023.  Based on this schedule there is still time to complete air permitting that includes PM2.5 NAAQS air quality modeling under the existing PM2.5 NAAQS or to complete permitting subject to the Prevention of Significant Deterioration (PSD) permitting program and not the nonattainment new source review (NNSR) permitting program which will be required if the area is determined to be in nonattainment with lower PM2.5 NAAQS.  However, time is running out fast and the regulated community should start considering evaluating impacts on future permitting efforts on a new revised PM2.5 annual NAAQS as low as 8 µg/m3 and a 24-hour PM2.5 NAAQS as low as 25 µg/m3.  In addition, once a draft rule is published the public will be afforded the opportunity to comment on the proposed revised PM2.5 NAAQS as part of the rulemaking process.

If a lower PM2.5 NAAQS is finalized in Spring of 2023 this will begin the process of local agencies assessing the attainment status with the new PM2.5 NAAQS.  The current 2018-2020 annual average PM2.5 NAAQS design value across all PM2.5 ambient monitors is approximately 7.8 µg/m3.  Currently only 21 of 519 PM2.5 ambient monitors 2018-2020 annual design value is greater than the current annual PM2.5 NAAQS (12 µg/m3).  If the PM2.5 annual NAAQS were lowered to 8 µg/m3 the number would jump to 221 of 519 PM2.5 ambient monitors being greater than a new proposed PM2.5 annual NAAQS mostly located around major metropolitan areas and most of the west coast.  This would mean NNSR permitting for these areas and less headroom for PM2.5 air quality modeling analyses.

Looking further ahead we can also expect that the U.S. EPA Office of Air Planning and Standards (OAQPS) Air Quality Modeling Group will likely also assess the adequacy of the PM2.5 Significant Impact Levels (SILs) if the PM2.5 NAAQS be lowered.  In addition, there are established PM2.5 24-hour and annual PSD increment levels; however, it is unlikely that the PM2.5 PSD increments would be changed based on the history of PSD increments and the fact that PSD increments are not health-based standards.

If you have any questions about a potential project that includes PM2.5 emissions or want to know how close your area’s ambient PM2.5 concentration is to the current PM2.5 NAAQS, 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: *