Ozone – the chemical compound O3 – is found both at ground level (i.e., ambient ozone) and in the upper portions of the Earth’s atmosphere (i.e., stratospheric ozone). In the upper atmosphere, ozone provides a protective layer from the harmful rays of the sun. However, in the ambient air, ozone is what is commonly referred to as smog. Unlike many pollutants, smog itself is not emitted directly into the air. Instead it is formed through a reaction of nitrogen oxides (NOx) and volatile organic compounds (VOCs) – known as ozone precursors – in the presence of sunlight. The major sources of NOx and VOCs are industrial facilities, electric utilities, mobile source exhaust, gasoline vapors and chemical solvents.
Because sunlight and hot weather contribute to its formation, smog most typically occurs in the summertime, however high concentrations of ozone have also been observed in cold months at a few high-elevation areas in the western U.S. where significant levels of local NOx and VOC emissions have combined to form ozone when snow is on the ground and temperatures are near or below freezing. Smog can occur at high concentrations in both urban and rural areas, and can exist in an area, or be exacerbated due to the phenomenon of transport, through which smog or its precursors can travel hundreds of miles.
Exposure to smog may contribute to premature death, particularly in people with heart and lung disease. Other adverse health effects associated with exposure to smog include reduced lung function, making normal breathing difficult; irritated airways, causing coughing, a scratchy or sore throat and shortness of breath; increased frequency of asthma attacks and aggravation of asthma and other chronic lung diseases, such as emphysema and bronchitis; and increased susceptibility to respiratory infection. Exposure to smog can also lead to more frequent doctor and emergency room visits, increased hospital admissions and lost work or school days. People with lung disease, children, older adults and people who are active outdoors may be especially susceptible to the ill effects of smog. Smog can also have serious effects on the ecosystem, including forests, wildlife refuges, wilderness areas, parks and sensitive vegetation like trees and plants.
On October 1, 2015, EPA issue a final rule revising the 2008 ozone National Ambient Air Quality Standards (NAAQS). After a lengthy review process, EPA Administrator Gina McCarthy determined a strengthing of the 2008 NAAQS was warranted and tightened the primary and secondary ozone NAAQS to to 70 parts per billion (ppb). Petitions challenging the new NAAQS - from both sides - have been filed in the U.S. Court of Appeals for the District of Columbia Circuit. In addition, work to implement the 2015 ozone NAAQS is now underway.
According to EPA, among the thousands of studies considered during the ozone NAAQS review were new clinical reports that provide information “clearly showing that ozone at 72 ppb can be harmful to healthy adults exercising.” The Administrator also examined analyses of people’s exposure to ozone and how ozone levels affect risk, with a particular focus on children’s exposure and risk. Based on the clinical studies and risk and exposure analyses, the Administrator concluded that a standard of 70 ppb “essentially eliminates exposures that have been shown to cause adverse health effects, protecting 99.5 percent of children from even single exposures to ozone at 70 ppb.” The Administrator further concluded that a 70-ppb standard provides the adequate margin of safety required under the law, protecting more than 98 percent of school-aged children from repeated exposures to ozone concentrations as low as 60 ppb, which is a 60-percent improvement over the current standard.
With this final action, the Administrator also revised the secondary (welfare-based) ozone standard to 70 ppb. In addition, the final rule expands the ozone monitoring season in 32 states and the District of Columbia, updates the Photochemical Assessment Monitoring Stations Network and the Federal Reference Method for monitoring and updates the Air Quality Index. EPA estimates the benefits of a 70-ppb standard to be $2.9 billion to $5.9 billion compared to projected costs of $1.4 billion, for a benefit-to-cost ratio of as much as 4:1.
With respect to nonattainment implications, based on 2012 to 2014 data, 241 counties (28 of which are in California) monitor ozone at levels that violate a 70-ppb standard. EPA indicates, however, that designations will likely be based on 2014 to 2016 data, which are expected to show improved air quality. Further, the agency projects that in 2025, a total of just 14 counties outside of California will continue to measure ozone in excess of 70 ppb. Attainment in the other counties, EPA expects, will occur largely from emission reductions from rules that target oxides of nitrogen (NOx) and volatile organic compounds (VOCs), as well as rules to reduce toxic and carbon emissions that yield collateral reductions in NOx and VOCs, including the Clean Power Plan, the Cross-State Air Pollution Rule, the Mercury and Air Toxics Standard, Tier 3 vehicle and fuel standards and various stationary source emissions standards.
As mentioned above, the interstate transport of air pollution across state boundaries from “upwind” sources can affect the ability of “downwind” states to attain and maintain the ozone and/or particulate matter NAAQS. With respect to smog, NOx emissions, and even ozone itself, can travel great distances affecting air quality and public health hundreds of miles away. The Clean Air Act includes provisions to address this transport in section 110(a)(2)(D)(i)(I) – the so-called “good neighbor” provisions. In March 2005, EPA issued the Clean Air Interstate Rule (CAIR) to help states address the problem of pollution from power plants that transports from one state to another. CAIR covers 27 eastern states and the District of Columbia and is based on a cap-and-trade system to reduce NOx and sulfur dioxide (SO2). Under CAIR, states must achieve the required emission reductions using one of two compliance options: 1) meet the state’s emissions budget by requiring power plants to participate in an EPA-administered interstate cap-and-trade system that caps emissions in two phases or 2) meet an individual state emissions budget through measures that the state chooses. After a legal challenge to CAIR, in July 2011, EPA promulgated the Cross-State Air Pollution Rule (CSAPR) to replace CAIR. CSAPR required many eastern and midwestern states to reduce power plant NOx and SO2 emissions that contribute to ozone and particulate matter pollution in downwind states. EPA’s CSAPR was challenged in court (EME Homer City Generation, L.P. et al., v. EPA, No. 11-1302) and in August 2012, the U.S. Court of Appeals vacated CSPAR and remanded it to EPA. The court also directed that CAIR be implemented until EPA issues a replacement rule.In March 2013, EPA and the American Lung Association each appealed the D.C. Circuit Court’s decision vacating CSAPR to the U.S. Supreme Court, which heard oral arguments on December 10, 2013. On April 29, 2014, the Supreme Court reversed the lower court’s decision and remanded the cases for further proceedings consistent with the Supreme Court’s decision. In early June 2014, the D.C. Circuit initiated those proceedings, whch culminated with oral arguments on February 25, 2015. On July 28, 2015, the DC Circuit issued its opinion and judgment in EME Homer City Generation v. EPA. The court revisited this case to 1) consider, on remand from the U.S. Supreme Court, several “as-applied over-control challenges” to EPA’s 2014 emissions budgets and 2) address a number of the petitioners’ broader challenges to the Transport Rule that it did not have occasion to address the first time it heard this case. The court granted in part and denied in part the petitions for review, invalidating and remanding a number of NOx and SO2 emissions budgets and rejecting all other challenges.