On February 7, 2024, the United States Environmental Protection Agency (USEPA) released a pre-publication version of a revised rule to decrease the National Ambient Air Quality Standard (NAAQS) for annual fine particulates (PM2.5) from 12 micrograms per cubic meter (ug/m3) to 9 ug/m3. The final rule was published on March 6, 2024, and became effective on May 6, 2024. The limits for the 24-hour PM2.5 standard (35 ug/m3), the secondary annual PM2.5 standard (15 ug/m3), and the PM10 standard (150 ug/m3) remain the same in the final rule. On September 5, 2024, the Illinois Pollution Control Board (IPCB) issued a proposed rule to revise the annual standard of PM2.5 from 12 ug/m3 to 9 ug/m3 codified in Title 35 of the Illinois Administrative Code (IAC) Part 243 to match the new NAAQS issued by USEPA.
Illinois must submit initial state attainment designations using 2021-2023 PM2.5 monitoring data no later than one (1) year after the promulgation date of the revised NAAQS (i.e., February 7, 2025). Within two (2) years of the final rule, USEPA must designate areas as either meeting (attainment) or not meeting (nonattainment) the standards. States and local agencies will then need to evaluate means to reduce pollution to meet these standards in nonattainment areas and maintain the attainment status for other areas. Attainment designations for the new annual PM2.5 standard will occur on February 7, 2026 at the earliest.
Historical Monitoring Data and Areas of Concern
Illinois Environmental Protection Agency (Illinois EPA) conducted monitoring and has recently published the data for PM2.5 in 2023. The statewide average was 9.95 ug/m3 in 2023. The charted 2021-2023 arithmetic mean values for PM2.5 are included in the figure below indicating several monitoring locations that exceeded the revised 9 ug/m3 annual standard and are good indicators for areas likely to be reclassified as nonattainment, including Chicago area, St. Louis area, and the Quad Cities.
Permitting & Modeling Impacts
New major sources or sources undertaking major modifications at existing facilities in attainment areas meeting the standards will need to obtain Prevention of Significant Deterioration (PSD) construction permits. These permitting requirements will include the need to conduct air dispersion modeling and evaluation of Best Available Control Technology (BACT) among other application components. For nonattainment areas, Nonattainment New Source Review (NNSR) construction permits will be required for new major sources or major modifications, either upon designation or afterwards. The NNSR application process includes the evaluation of Lowest Achievable Emission Rate (LAER) requirements as well as obtaining emission offsets for the proposed project.
USEPA also issued the Supplement to the Guidance on Significant Impact Levels for Ozone and Fine Particles in the Prevention of Significant Deterioration Permitting Program memo on April 30, 2024. This memo outlines the reassessed significant impact levels (SILs) for the 24-hour PM2.5 NAAQS and PSD increments that the Agency recommends States use in the PSD permitting program based on new ambient air quality data and the PM2.5 NAAQS revision. USEPA has lowered the SIL for the primary annual PM2.5 NAAQS and PSD increment from 0.3 ug/m3 to 0.13 ug/m3 and recommended that the 1.2 ug/m3 value for the 24-hour PM2.5 SIL be retained.
The updated annual PM2.5 standard and SILs may impact new projects or modifications to facilities in Illinois. Trinity is continuing to track the impacts of these changes as well as the impact these changes have on Illinois EPA rulemaking. Trinity has the expertise in air quality permitting and dispersion modeling to assist navigating through the impacts to current and planned projects. For more assistance, contact our Trinity Chicago office experts Brad Berglund, Chloe Reece, or Anna Aumann.
