Exceptional Events Demonstration to Support Attainment Designation Recommendations for 2024 Annual PM2.5 NAAQS

2024 PM2.5 Designation Recommendation and Associated Exceptional Events Demonstration 

The North Carolina Department of Environmental Quality, Division of Air Quality (DAQ), hereby gives notice regarding its Pre-hearing Draft of the Exceptional Events Demonstration to Support Attainment Designation Recommendations for the 2024 Annual PM2.5 National Ambient Air Quality Standard (NAAQS) for Mecklenburg and Davidson Counties, North Carolina (June – July 2023 Canadian Wildfire Smoke Impacts). 

Based on certified monitoring data for 2021-2023, the Remount Road monitor (371190045) in Mecklenburg County and Lexington Water Tower monitor (370570002) in Davidson County have a rounded design value of 9.2 micrograms per cubic meter. The North Carolina Division of Air Quality (DAQ) reviewed the monitoring data and determined that Canadian wildfire smoke-laden air masses significantly increased PM2.5 concentrations measured by these two monitors during four multi-day events in June and July of 2023. These events were significant enough to increase the three-year average design value for each of the two PM2.5 monitors to slightly above the revised standard. 

In accordance with EPA’s Exceptional Events Rule (40 CFR 50.14(c)(3)), the DAQ prepared this Exceptional Events demonstration to show that Canadian wildfire smoke significantly increased PM2.5 concentrations four events. If it were not for these exceptional events, the design value for each monitor would be below the revised standard. Based on the technical analyses presented in the Exceptional Events demonstration, the DAQ is requesting that EPA exclude days highly impacted by Canadian wildfire smoke from the design value for each monitor to show attainment of the revised primary annual PM2.5 standard. This document has been prepared to support the State of North Carolina’s designation recommendations for the 2024 revised primary annual PM2.5 NAAQS which must be submitted to EPA by February 7, 2025.

Any person wishing to comment may submit a written statement for inclusion in the record of proceedings regarding the pre-hearing draft of the Exceptional Events Demonstration to Support Attainment Designation Recommendations for the 2024 Annual PM2.5 National Ambient Air Quality Standard (NAAQS) for Mecklenburg and Davidson Counties, North Carolina (June – July 2023 Canadian Wildfire Smoke Impacts). A public hearing will be held on Friday, December 20, 2024, if requested by Friday, December 13, 2024. Written comments should be submitted electronically to daq.publiccomments@deq.nc.gov or postmarked no later than Friday, December 20, 2024. (Please type “EE Demonstration” in the subject line)