Air Quality Division: Natural and Exceptional Events

In 2005, Congress identified a need to account for events that result in exceedances of the National Ambient Air Quality Standards (NAAQS) that are exceptional in nature (e.g., not expected to reoccur or caused by acts of nature beyond man-made controls). In response, the U.S. Environmental Protection Agency (EPA) promulgated the Exceptional Events Rule (EER) to address exceptional events in 40 CFR Parts 50 and 51 on March 22, 2007 (72 FR 13560). On May 2, 2011, the U.S. EPA released draft guidance documents on the implementation of the EER to State, tribal, and local air agencies for review. On May 10, 2013, the EPA released interim guidance documents (see below) to clarify key provisions of the 2007 EER in response to questions and issues that have arisen since the rule was promulgated.

Due to the arid nature of the state, Arizona is susceptible to both windblown dust events and smoke events from forest fire, both of which may qualify as exceptional events. These events may be captured by various air quality monitoring equipment throughout the state, sometimes resulting in exceedances or violations of the NAAQS. The EER allows for states and tribes to "flag" air quality monitoring data as an exceptional event and exclude that data from use in determinations with respect to exceedances or violations of the NAAQS, if the U. S. EPA concurs with the demonstration submitted by the flagging agency.

Below is information about the Exceptional Event Rule (EER) and how this rule affects planning throughout the State of Arizona

Natural and Exceptional Events Demonstration Documentation

Natural and Exceptional Event Plans

Additional Documents