Wildfire Smoke,the Clean Air Act, and the ExceptionalEvents Rule: Implications and Policy Alternatives

In recent years, increasing wildfire activity in the western US and Canada has driven declining air quality in some regions of the US. Under EPA’s Exceptional Events Rule, states are allowed to exempt daily pollution monitor readings impacted by wildfire smoke from determinations of compliance with Clean Air Act air quality standards. As a result, wildfire smoke is leading to a growing divergence between actual and regulatory air quality. This paper reviews treatment of wildfire smoke under the Clean Air Act and the Exceptional Events Rule. It presents quantitative evidence on the effect of the rule on fulfillment of air quality standards, and an analysis of the degree to which smoke that currently leads to air quality violations is driven by out-of-state fires and fires on federal lands. We suggest a modification to the Exceptional Events Rule under which wildfire emissions would be excluded from air quality regulations only if states adopt government-defined best fire management policies, and we discuss the legal and practical feasibility of such a change.