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EPA's Ozone Transport Rulemaking
EPA's Strategy for Reducing Transported Ozone
Ground level ozone is not emitted directly into the air, but rather is formed when oxides of nitrogen (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight. Ozone "precursors," such as NOx emissions, as well as ozone itself, can be carried hundreds of miles from their origins, causing air pollution over wide regions.
Many urban areas have already made efforts to control ozone by greatly reducing local VOC emissions. While this has improved air quality, incoming ozone transported from upwind areas has made achieving the National Ambient Air Quality Standards difficult in many areas. A major scientific study, conducted by the Ozone Transport Assessment Group (OTAG), concluded that reductions in NOx emissions, from both rural and urban areas, can reduce the ozone transported into urban areas and help those areas meet the air quality standards.
EPA's Ozone Transport Rulemaking
On October 27, 1998, after considering the OTAG research and other evidence, EPA promulgated a rule requiring 21 states and the District of Columbia to reduce NOx emissions. (63 FR 57356) (This rule is commonly known as the NOx SIP Call.) The rule specifies how much each state must cut its NOx emissions; however, it does not mandate how each state must make these cuts. Instead, states are given the flexibility to develop their own plans and sets of rules for reducing emissions. These State Implementation Plans (SIPs) were to have been submitted to EPA by October 30, 2000, with the emission reduction measures to be in place by May 31, 2004. In the event that a state does not submit an approvable SIP, EPA is required to promulgate a Federal Implementation Plan (FIP). This FIP would require the same amount of reductions that would have been required by the state's NOx SIP.
Further Health and Environmental Benefits of Reducing NOxIn addition to contributing to attainment of ozone air quality standards, decreases in NOx emissions will help to improve the environment in several other important ways. (Link to the EPA brochure How Nitrogen Oxides Affect the Way We Live and Breathe for more information.)
- On a national scale, decreases in NOx emissions will also decrease acid deposition, nitrates in drinking water, excessive nitrogen loadings to aquatic and terrestrial ecosystems, and ambient concentrations of nitrogen dioxide, particulate matter and toxics.
- On a global scale, decreases in NOx emissions will, to some degree, reduce greenhouse gases and stratospheric ozone depletion.
These benefits were also specifically recognized by OTAG, which in its July 8, 1997 final recommendations, stated that it "recognizes that NOx controls for ozone reductions purposes have collateral public health and environmental benefits, including reductions in acid deposition, eutrophication, nitrification, fine particle pollution, and regional haze."
Links to Additional InformationA fact sheet in PDF format on the NOx SIP call and associated proposals. (A free copy of Adobe Acrobat Reader can be downloaded here
.)
How Nitrogen Oxides Affect the Way We Live and Breathe A brochure in PDF format containing information on health and environmental impacts of NOx, and EPA's efforts to reduce NOx.
- The Regional Transport of ozone: New EPA rulemaking on Nitrogen Oxide Emissions A brochure in PDF format containing information on NOx emissions, the NOx SIP call, and EPA's market-based emissions trading program.
- The Office of Air Quality Planning and Standards' Ozone Transport Rulemaking Page: Rulemaking actions, public hearing information and more.
- Automobile Emissions: An Overview: In the past 10 years NOx emissions from highway vehicles decreased by more than 5 percent, while vehicle miles traveled increased significantly. Link to an overview of automobile emissions and emission reduction strategies.
- The Acid Rain Home Page: Information on the acid rain program, NOx reductions and NOx trading programs.