On January 6, 2023, the U.S. Environmental Protection Agency (EPA) announced its proposed decision to revise the National Ambient Air Quality Standard (NAAQS) for particulate matter. The NAAQS are set to air quality levels in outdoor air that “provide public health protection, including protecting the health of ‘sensitive’ populations such as asthmatics, children, and the elderly.” The change intends to strengthen a key NAAQS for fine particulate matter smaller than 2.5 microns, also known as PM2.5.
While the proposed NAAQS rule if implemented would likely not have significant impact across most of the northeastern United States, reducing the PM standard will lower the compliance threshold in situations where air quality dispersion modeling is used to document compliance with the NAAQS, such as new air permit applications. While there would be a transition period, there would likely be pressure on applicants to meet the new standard immediately.
The agency’s proposal would reduce the annual standard from its current level of 12.0 micrograms per cubic meter (µg/m3) to within the range of 9.0 to 10.0 µg/m3. EPA is proposing that other standards, including the short-term standard, remain the same. A 60-day comment period will begin once the proposal is published in the Federal Register.
Should a strengthening of the standard be implemented, a two-year period will commence during which EPA will determine what parts of the country are generally not meeting the standard, followed by an 18-month period where states propose actions to reduce emissions to achieve compliance with the revised standard. This will eventually require Lowest Achievable Emission Rate (LAER) and offsets for new stationary sources of particulate matter, and of pollutants that can create particulate matter in the atmosphere (e.g., NO2).
Air quality, including levels of particulate matter have improved over the years, however, there remain many counties across the US that are out of compliance with the NAAQS. A lower standard will result in even more counties being in a position of non-compliance. US EPA estimates that about 24 additional counties will exceed an annual standard of 10 µg/m3 , mostly in California and this number jumps to about 50 with an annual standard of 9 µg/m3 (starting with a baseline at 12 µg/m3) Yet even if in compliance with the revised standard, both existing facilities and new project applicants should be informed and prepared to prove compliance with the new standards.
For more details and a link to the proposed rule, see: National Ambient Air Quality Standards (NAAQS) for PM | US EPA.
- The NAAQS are set to an air quality level in outdoor air that provides public health protection, including protecting sensitive populations, such as children.
- The proposed change intends to strengthen a key NAAQS for fine particulate matter smaller than 2.5 microns, also known as PM2.5.
- Even if an area is in compliance with the revised standard, both existing facilities and new project applicants should be informed and prepared to prove compliance with the new standards.
- A 60-day comment period will begin once the proposal is published in the Federal Register.
Sonja Sax, M. S., Sc.D, is an environmental health scientist that specializes in evaluating exposure and health risk from environmental pollutants. Dr. Sax has over 20 years of experience in environmental regulatory assessment, health impact assessment and cost-benefit analyses. Sonja has managed large multi-year projects advocating for clients involved in litigation or providing permitting support. She has performed indoor and outdoor air quality investigations evaluating exposures and health impacts of airborne gases and particles. In 2019, she served as an advisor to the US EPA Clean Air Scientific Advisory Committee for the particulate matter and ozone National Ambient Air Quality Standards.