The US National Ambient Air Quality Standards (NAAQS) are the centerpiece of the US Clean Air Act (CAA) and establish allowable concentration levels for six “criteria air pollutants”: ozone, particulate matter, lead, carbon monoxide, nitrogen dioxide, and sulfur dioxide. The CAA requires the US Environmental Protection Agency (EPA) to review and, as appropriate, revise the NAAQS at least every five years, and EPA has, since 1970, regularly adopted increasingly stringent standards. Whether those revisions have gone far enough or too far has become a predictably contentious issue, with each review involving debates over science, the role of EPA’s Clean Air Science Advisory Committee (CASAC), the discretion of the EPA Administrator, and the format of the review process itself, among many other issues.
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When an adverse party challenges final rules that are favorable to particular companies, those companies and their trade associations sometimes question whether it is worth their time and effort to intervene on EPA’s side to help the Agency defend its action. A recent D.C. Circuit decision shows that sometimes an argument made by a Respondent-Intervenor can be decisive.
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In October 2015, EPA reduced the level of the National Ambient Air Quality Standards (“NAAQS”) for ozone from 75 parts per billion (“ppb”) to 70 ppb. What is happening concerning implementation of those NAAQS?

Although litigation over EPA’s decision to lower the ozone NAAQS remains in abeyance as the Trump Administration continues to consider whether the Agency should reconsider the rule or some part of it, the 2015 standard itself has not been stayed. Thus, the Clean Air Act requires that implementation of the standard proceed. One key step in implementation is promulgation by EPA of a list of areas where the standard is violated, including areas that contribute to standard violations in nearby areas. EPA’s identification of these “nonattainment” areas is a trigger for many of the Act’s control requirements.
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Litigation concerning the ozone air quality standards that EPA adopted in 2015 has been placed in abeyance, as the Trump administration decides whether to reconsider the standards. The standards remain in effect, however, and statutory implementation deadlines are approaching. What are those deadlines and what options exist for staying the standards until after any reconsideration proceedings are completed?
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