Treatment of Data Influenced by Exceptional Events

The Environmental Protection Agency (EPA) is finalizing revisions to certain sections within the regulations that govern the exclusion of event-influenced air quality data from certain regulatory decisions under the Clean Air Act (CAA). The EPA's mission includes preserving and improving the quality of our nation's ambient air to protect human health and the environment, and the CAA and the EPA's regulations rely heavily on ambient air quality data. However, the CAA also recognizes that it may not be appropriate to use the monitoring data influenced by "exceptional" events that are collected by the ambient air quality monitoring network when making certain regulatory determinations. When "exceptional" events cause exceedances or violations of the national ambient air quality standards (NAAQS) that subsequently affect certain regulatory decisions, the normal planning and regulatory process established by the CAA may not be appropriate. This final rule contains definitions, procedural requirements, requirements for air agency demonstrations, criteria for the EPA's approval of the exclusion of event-influenced air quality data and requirements for air agencies to take appropriate and reasonable actions to protect public health from exceedances or violations of the NAAQS. It reflects the experiences of the EPA, state, local and tribal air agencies, federal land managers and other stakeholders in implementing this program over the past 10 years. These regulatory revisions, the EPA's commitment to improved communications, our focus on decisions with regulatory significance, and the expressed non- binding guidance in the preamble regarding recommendations for demonstration narrative and analyses to include in demonstration packages, protect human health and the environment while providing needed clarity, increasing the administrative efficiency of demonstration submittal process, and removing some of the challenges associated with implementing the Exceptional Events Rule.