| Reducing Tropospheric Ozone Pollution | |
Ozone is one of six "criteria air pollutants" identified by the U.S. Environmental Protection Agency. Each of the criteria air pollutants is subject to air quality standards created by the EPA. The national ambied air quality standards (NAAQS) are set to protect human health with an "adequate margin of safety." In the United States, the ozone concentration is measured on a local scale. The map of the United States illustrates counties that have exceeded the EPA’s standards for ozone air quality. Currently, the EPA standards require that 8-hour average concentration of ozone should not exceed 0.8 ppm. An area is out of compliance, if the three year average of the fourth-highest 8-hour average concentration is greater than 0.8 ppm (EPA 2007).
http://www.epa.gov/oar/oaqps/greenbk/map8hrnm.html
http://www.epa.gov/airtrends/ozone.html#oznat |
The Clean Air Act requires that states be in compliance with the national ambient air quality standards. There are processes in place that provide guidance to areas that have not met the standards. State implementation plans (SIPs) are required for states that are not in compliance with the NAAQS. Several regulations have recently been enacted to further reduce ozone in the southeastern U.S.: 1) NOx SIP call -- Due to regional transport of NOx across state boundaries, the SIP call requires 22 states in the eastern U.S. and the District of Columbia to submit plans that address the transport of ozone (and precursor pollutants) throughout the region. 2) Clean Air Interstate Rule (CAIR) -- The rule plans to cap emissions of sulfur dioxide and NOx in the eastern United States. A cap-and-trade systems will eventually reduce the sulfur dioxide and NOx emissions by 60-70% over 2003 levels. Also, further research is needed to understand the role of the NOx/VOC ratio in the creation of ozone. In some regions, a narrow focus on reducing NOx without reducing VOC concentrations could result in increased levels of ozone. A better understanding of the NOx/VOC ratio could help areas with persistent ozone problems find new solutions. |
