EPA Lowers the 8-Hour Ozone Standard to 0.075 ppm

On March 12, 2008, the Environmental Protection Agency (EPA) announced its decision to revise the 8-hour ozone National Ambient Air Quality Standard (NAAQS) to 0.075 parts per million (ppm). Under the Clean Air Act (CAA), EPA is required to establish a primary NAAQS for a pollutant at a level that is requisite to protect public health with an adequate margin of safety. The agency cannot take cost or implementation issues into consideration when issuing the NAAQS. The current ozone standard is 0.08 ppm, but areas may have ozone concentrations as high as 0.084 ppm and still be considered in attainment with the standard due to the way in which the measurements are rounded.

The revised 8-hour ozone NAAQS is less stringent than the level recommended by EPA’s Clean Air Scientific Advisory Committee (CASAC), an independent panel that advises EPA on technical and scientific issues related to air quality standards. In October 2006, CASAC unanimously recommended that EPA set the 8-hour ozone standard at a level between 0.060 and 0.070 ppm and emphasized that the standard should not be higher than 0.070 ppm in order to protect public health.

Approximately 85 areas are classified as in nonattainment with the 0.08 ppm 8-hour ozone standard. Based on 2004-2006 data, EPA estimated that 345 counties currently are not meeting the 0.075 ppm 8-hour ozone NAAQS.  Although this number may change based on the 2006-2008 monitoring data that will be the basis of the attainment designations, many states may have to significantly increase their efforts to achieve additional emission reductions.

EPA anticipates that it will ask for state recommendations regarding attainment designations by March 2009, which will be based on 2006-2008 monitoring data. EPA intends to issue final 8-hour ozone attainment designations under the revised standards by March 2010, with state implementation plans (SIPs) due three years later. Depending on the severity of a state’s nonattainment status, states could have up to 17 years to comply with the new standard.

The 1997 8-hour ozone NAAQS will remain in place until EPA issues a rulemaking on implementation of the new standard, which is likely to be part of the same regulatory package as the attainment designations.  The agency also will issue a separate rulemaking, scheduled to be proposed in June 2008 and finalized by March 2009, on air quality monitoring under the revised ozone standard.  Among the issues to be addressed in this rule are requirements for both urban and rural areas that do not currently have air quality monitors, defining boundaries of the new ozone nonattainment areas, and extending the length of the ozone season in some parts of the nation.

Secondary Standard

The CAA also requires EPA to set a secondary ozone NAAQS at a level that is requisite to protect the public welfare from adverse effects.  "Public welfare" is defined to include, without limitation, effects on soils, water, crops, vegetation, and climate, as well as effects on economic values and on personal comfort and well-being. The new secondary standard will be set at the same level as the primary standard, consistent with past agency practice. EPA considered, and rejected, an alternative that would have established a cumulative seasonal standard, concluding that this approach had only uncertain benefits and may be more than what is requisite to protect the public welfare.  The proposed cumulative standard would have been based on 12-hour daily ozone measurements, as well as measurements recorded over the three-month summer ozone season, with higher ozone concentrations given greater weight when cumulating the measurements.

Form of the Standards

In contrast to the 1997 standard, the primary and secondary revised 8-hour ozone NAAQS are specified to three decimal places.  Ozone concentration monitors measure to the third decimal place; thus, no rounding will be required.  Otherwise, the form of the 8-hour ozone standards remains unchanged and attainment will be based on the three-year average of the annual fourth-highest daily maximum 8-hour concentration.

Implications and Next Steps

In light of the significant expected increase in the number of nonattainment areas, compliance with more stringent 8-hour ozone standards will likely require additional emission reductions from a variety of emissions sources.  Those sources potentially targeted include motor vehicles, electric generating units, other industrial sources, gasoline vapors, and chemical solvents.  Each of these source categories contribute to emissions of nitrogen oxide (NO_x) and volatile organic compounds (VOCs) that form ozone. The regulatory focus will be on controlling NO_x and VOC emissions, but other ozone precursors could also be targeted. Some of the reductions may be achieved through recently promulgated EPA programs, including the Clean Air Interstate Rule (CAIR), the Clean Air Visibility Rule (CAVR), and various mobile source emission control programs that are currently being implemented.  The increased number of ozone nonattainment areas is likely to increase the difficultly of new major stationary sources of NO_x and VOC emissions to obtain pre-construction review permits under the New Source Review (NSR) program.  Finally, it is likely that the revised primary or secondary 8-hour ozone standards, or both, will be the subject of legal challenges contending that they are not sufficiently protective of public health and welfare to comply with CAA requirements.