	Introduction

On October 1, 2015, under the authority of Sections 108 and 109 of the Clean Air Act (CAA) as amended, the Environmental Protection Agency (EPA) finalized revisions to the National Ambient Air Quality Standards (NAAQS) for ground-level ozone from the then-current level of 75 parts per billion (ppb) to 70 ppb. As described in detail below (see " Implementation of the 2015 Standards "), under the CAA, revision of the standards sets in motion a process in which states and EPA identify areas that do not meet the standards ("nonattainment areas") and the states prepare implementation plans to demonstrate how emissions will be lowered sufficiently to reach attainment in those areas. These health effects include aggravated asthma, chronic bronchitis, and heart attacks, and in some cases premature death. California was excluded from EPA's estimate of both costs and benefits of the nationwide standard, because most areas of the state will have until the 2030s to reach attainment of the NAAQS. In the RIA, EPA estimated the economic value of the benefits of reducing ozone concentrations to 70 ppb (for areas other than California) at $2.9-$5.9 billion annually by 2025, with costs at $1.4 billion annually in 2025. The actual nonattainment designations promulgated in 2018 are in most cases based on 2014-2016 monitoring data and include just over 200 counties or partial counties in 22 states and the District of Columbia, plus two tribal areas. These national standards apply to products that contribute to ozone and other criteria pollution (particularly mobile sources, such as automobiles) and to stationary emission sources (such as power plants). As a result, a more stringent primary standard and a different version of the secondary standard were proposed in January 2010. EPA staff also recommended strengthening the primary standard. The impact of these regulations on wintertime ozone concentrations is yet to be determined, but interestingly the Upper Green River Basin, which was designated nonattainment under the 2008 ozone NAAQS, has been designated attainment for the 2015 standard. The dollar value of the avoided premature deaths accounts for 94% to 98% of EPA's total monetized benefits. California and Other Regional Costs and Benefits

EPA provided separate cost and benefit estimates for California. H.R. The House passed H.R. The agency did not agree. As noted earlier, the House passed H.R. The requirements were not finalized. 806 (Representative Olson), the Ozone Standards Implementation Act, would delay the deadline for designation of nonattainment areas under the 2015 ozone NAAQS revision until October 2025 and the date for State Implementation Plan revisions under the standard until October 2026; would require future reviews of the NAAQS at 10-year rather than five-year intervals; would allow the Administrator to consider, as a secondary consideration, likely technological feasibility in establishing and revising primary NAAQS in cases where the Administrator concludes that a range of levels of air quality for a pollutant are requisite to protect public health with an adequate margin of safety; would require the Administrator to publish regulations and guidance for implementing a new or revised NAAQS concurrently with the publication of the standard; would make changes to EPA's authority to exclude from air quality monitoring data used to determine attainment of NAAQS certain data influenced by "exceptional events"; would require a report to Congress on the impact of emissions originating outside the United States on attainment and maintenance of NAAQS; and other provisions.
Implementation of revised ozone standards by the U.S. Environmental Protection Agency (EPA) is now moving forward, after the agency designated 52 areas with just over 200 counties or partial counties and two tribal areas as "nonattainment" for the standards. The standards—formally known as National Ambient Air Quality Standards (NAAQS) for ground-level ozone—are standards for outdoor (ambient) air. In 2015, EPA tightened both the primary (health-based) and secondary (welfare-based) standards from 75 parts per billion (ppb) to 70 ppb after concluding that protecting public health and welfare requires lower concentrations of ozone than were previously judged to be safe. Ozone aggravates heart and lung diseases and may contribute to premature death; the primary standard addresses these concerns. Ozone can also have negative effects on forests and crop yields, which the secondary NAAQS is intended to protect.
The designated nonattainment areas include counties in 22 states and the District of Columbia. Most of these areas have had previous experience as nonattainment for earlier versions of the NAAQS. Designation as nonattainment imposes more stringent permitting and pollution control requirement for new and modified stationary sources of emissions as compared with the requirements in areas that are in attainment of the NAAQS, and requires the development of State Implementation Plans demonstrating how emissions will be reduced sufficiently to reach attainment.
EPA estimates the cost of meeting the 70 ppb standard in all states except California at $1.4 billion annually in 2025. Because most California areas would have until the 2030s to reach attainment, EPA provided separate cost estimates for California ($0.80 billion annually, post-2025). These cost estimates are substantially less than those from the National Association of Manufacturers and other industry sources, which have been widely cited. The benefits of reducing ozone concentrations were estimated by EPA at $2.9-$5.9 billion annually by 2025. The dollar value of avoided premature deaths accounts for 94% to 98% of this estimate.
The agency projects that most areas will be able to reach attainment of the new standards by 2025 as a result of already promulgated regulations for gasoline, autos, power plants, and other emission sources. These regulations are being implemented independently of the 2015 NAAQS revision.
Members of Congress have shown particular interest in whether the expected benefits of the standards justify their projected costs. There is controversy over the methods used to estimate both costs and benefits. As the Clean Air Act is currently written, however, the agency is prohibited from weighing costs against benefits in setting NAAQS standards. The statute simply directs EPA to set the primary standard at a level requisite to protect public health, allowing an adequate margin of safety.
Various interest groups have lobbied against strengthening the standards. In the 115th Congress, the House has passed H.R. 806 to delay implementation of the 2015 NAAQS until the mid-2020s and to make changes to the process of future NAAQS revisions. The House Appropriations Committee reported a similar delay as a rider to EPA's 2018 appropriation (in Section 432 of H.R. 3354), but the final version of the appropriation (in H.R. 1625/P.L. 115-141) did not include the rider.