Introduction
It is not uncommon for the U.S. Environmental Protection Agency (EPA) to tighten its national ambient air quality standards (NAAQS) to address new understandings of the effects of air pollution on humans and the environment. But as EPA moves forward with a proposal to make the ozone NAAQS more stringent, the Agency is likely ushering in a new reality for the western United States: where EPA sets a standard for concentrations of ozone in the ambient air that may be unachievable regardless of the actions taken by state regulators and the reductions achieved by anthropogenic sources of emissions. The problem in the Intermountain West is that EPA is advancing a revised ozone NAAQS that appears to be at or below the background concentration that exists in much of the region; in large areas across the western United States, prevailing ozone concentrations are attributable to other mechanisms, namely, stratosphere-to-troposphere ozone intrusion, naturally occurring ozone from sources like wildfires, and international ozone transport into the Intermountain West from sources
in Asia.
None of these sources of ozone can be effectively controlled by the states that are required to attain the new standard. As a result, one of the central themes that EPA will be faced with—in both finalizing the rule and defending the judicial challenges that are almost certain to follow—is whether EPA can lawfully impose and defend a standard that is unattainable by the means available under the Clean Air Act (CAA).
