State environmental regulators are beginning to develop plans designed to meet more stringent air quality standards under the Clean Air Act (CAA), including standards to protect against unhealthful levels of ground-level ozone. In doing so, many states are looking more closely at a factor that contributes to their air quality problems but that they lack any authority to address: the phenomenon of air pollution carried by prevailing winds into their jurisdictions from emission sources located not only outside their own state borders but outside the US itself. The issue of international contributions to air quality concerns has gained currency in part due to the many challenges states face in meeting the stringent nationwide air quality standards for ground-level ozone that the US Environmental Protection Agency (EPA) adopted in 2015.

Last year, EPA issued regulations formally designating over 50 areas, located in many parts of the US, as “nonattainment” for those 2015 ozone standards. These are areas in which air quality has not yet improved sufficiently to meet the 2015 standards. Areas designated nonattainment for those standards include many large metropolitan areas such as Los Angeles, New York City, Chicago, Houston, Dallas, Denver and Atlanta, and also several much less densely populated areas, like Allegan County, Michigan, and Yuma, Arizona. Under the CAA and EPA regulations, the vast majority of ozone nonattainment areas are classified as “marginal” nonattainment, meaning their air quality is only slightly worse than the standards. In fact, outside California, only one nonattainment area for the 2015 standards (New York City) currently has a more serious classification than marginal. Because their air is close to meeting the standards, marginal areas are not required to impose major new emission controls—as long as those areas remain within their marginal classification. But the downside for marginal areas is that if they don’t achieve attainment within three years after EPA issued nonattainment designations (in this case, by 2021), then those areas will be “bumped up” to a more serious classification, a step that triggers more onerous emission control regulations. Such regulations typically entail imposition of costly new control requirements not only for large industrial facilities but also, in some cases, for a variety of smaller business enterprises.

Many marginal areas may well achieve attainment of the 2015 ozone standards by their 2021 deadline through, for example, declining motor vehicle emissions resulting from EPA’s tailpipe controls for newer vehicles and engines. But some of these areas may be unable to reach the attainment goal by then. Even so, such areas may still be able to avoid being bumped up to more serious classifications thanks to a provision of the CAA that has attracted relatively little attention but offers the prospect of relief where attainment would occur “but for” emissions coming from outside the nation’s borders.

That statutory provision—section 179B(b) of the CAA (42 U.S.C. § 7509a(b))—specifies that “[n]otwithstanding any other provision of law, any State that establishes to the satisfaction of the [EPA] Administrator that, with respect to an ozone nonattainment area in such State, such State would have attained the national ambient air quality standard for ozone by the applicable attainment date, but for emissions emanating from outside of the United States, shall not be subject to” CAA provisions that include, as EPA has explained, the classification bump-up provisions. See EPA, “Implementation of the 2015 National Ambient Air Quality Standards for Ozone: Nonattainment Area State Implementation Plan Requirements; Final Rule,” 83 Fed. Reg. 62,998, 63,009-10 (Dec. 6, 2018); EPA, “Determinations of Attainment by the Attainment Date, Extensions of the Attainment Date, and Reclassification of Several Areas Classified as Moderate for the 2008 Ozone National Ambient Air Quality Standards; Proposed Rule,” 83 Fed. Reg. 56,781, 56,783 (Nov. 14, 2018); EPA, “State Implementation Plans; General Preamble for the Implementation of Title I of the Clean Air Act Amendments of 1990,’’ 57 Fed. Reg. 13,498, 13,569 (Apr. 16, 1992).

Results of recent EPA air quality modeling suggest that significant amounts of ozone in many US nonattainment areas result from foreign emissions, which no US state has authority to control. Foreign emission sources include those in Canada and Mexico as well as sources located in countries farther afield (contributing emissions to what EPA modelers sometimes label “Initial & Boundary,” or simply “Boundary,” air quality conditions). One organization recently petitioned Colorado to have that state prepare a section 179B(b) demonstration for the Denver nonattainment area with respect to a less stringent ozone standard that EPA published in 2008. And California, last year, submitted to EPA an analysis—again, with respect to the 2008 ozone standard—making the case that Imperial County in that state was entitled under section 179B(b) to avoid being bumped up to a more serious classification due to emissions from Mexico.

As states begin to consider efforts to comply with the more stringent 2015 ozone standards, increased attention to air quality impacts from non-US emissions—and, potentially, some degree of relief under CAA section 179B(b) for affected states—may be expected.