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This proposed action will revise the Exceptional Events rulemaking to clarify and streamline certain rule elements, including, but not limited to, those associated with high wind dust events, historical fluctuations, the "not reasonably controllable or preventable" criterion, and the "but for" criterion. On March 22, 2007, the EPA promulgated the "Treatment of Data Influenced by Exceptional Events; Final Rule" pursuant to the 2005 amendment of Clean Air Act. This rule, known as the Exceptional Events Rule (EER), superseded the EPA's previous natural events guidance and those sections of the interim fire policy document that address exceptional events. The EER created a regulatory process. These regulatory sections contain definitions, procedural requirements, requirements for air agency demonstrations, and criteria for the EPA approval for the exclusion of air quality data from regulatory decisions under the EER. Since EPA promulgated the EER in 2007, numerous interested parties have raised questions and issues regarding implementation of the rule.