Contact EPA Pacific Southwest Air Program
Pacific Southwest, Region 9
Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations
Air Quality Analysis
NOTE: This content is no longer being updated. The most up to date information can be found in Federal Register Notices and Approved Air Quality Implementation Plans in Region 9.
Exceptional Events
On March 22, 2007, EPA adopted the Treatment of Data Influenced by Exceptional Events rule to govern the review and handling of certain air quality monitoring data for which the normal planning and regulatory processes are not appropriate. Under the terms of the rule, EPA may exclude monitored exceedances of the National Ambient Air Quality Standards from consideration when designating an area as nonattainment, redesignating an area as nonattainment or reclassifying an existing nonattainment area to a higher classification if a state adequately demonstrates that an “exceptional event” caused the exceedances. Before EPA will exclude data from these regulatory determinations, the state must flag the data in EPA’s AQS database and, after notice and an opportunity for public comment, submit a demonstration to justify the exclusion. After considering the weight of evidence provided in the demonstration, EPA will decide whether or not to concur on each flag.