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October 19, 2007
Emily Elliott 412-624-8882 eelliott@pitt.edu
Denver Makle 703-648-4732 dmakle@usgs.gov

USGS Study Identifies Major Source of Nitrate in Precipitation

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Nitrate found in precipitation occurring in rural areas of the Northeastern and Midwestern United States is primarily caused by emissions from stationary sources located hundreds of miles away, according to a new U.S. Geological Survey (USGS) study.

Stationary sources include coal-burning power plants and other industrial facilities. Although vehicles are the single largest emission source of nitrogen oxides in this region, distant stationary sources may have a greater impact on nitrate found in rain and snow.

"These results demonstrate that we have a new chemical analysis tool for tracing the influence of emissions from stationary sources. This could be a powerful method for monitoring the effects of stationary source emission reductions slated for this region over the next 8 years," says Emily Elliott, former USGS scientist and current assistant professor at the University of Pittsburgh.

The study, published in the journal Environmental Science and Technology, presents the first large-scale investigation of nitrogen isotopes in precipitation.  The authors analyzed stable nitrogen isotopes at 33 long-term National Atmospheric Deposition Program (NADP) monitoring sites. The NADP is a cooperative nationwide program that measures air pollutant concentrations in rain and snow at more than 250 stations across the United States, most of which are deliberately located in relatively rural settings away from urban, industrial or agricultural centers.

Nitrogen oxides originate from the burning of fossil fuels, including emissions from motor vehicles, electric utilities and other sources. Power plants and other stationary sources emit pollutants high in the atmosphere that can be transported for long distances before falling to the ground, while vehicles emit pollutants through tail pipes close to the ground where they are more likely to be deposited over shorter distances near roadways.  Further, a portion of emissions from all sources may be deposited on the landscape in gaseous forms such as aerosols and particles in addition to precipitation. Thus the authors urge caution when interpreting their results, stating that both stationary sources and vehicles are important contributors to air pollution throughout the region. "Our results highlight the need to improve our understanding of the fate of vehicle emissions; one way we can do this is by expanding monitoring networks to include more urban sites," says Elliott.

Nitrogen oxides in the atmosphere are a primary societal concern, given their contributions to a wide variety of environmental and health impacts. Nitrate is an important contributor to acid rain and can result in acidification of streams and soils, forest decline and coastal water degradation. Determining the fate of major sources of nitrogen emissions is necessary to develop sound regulatory and mitigation strategies.

The research was supported by the New York State Energy Research and Development Authority and the Electric Power Research Institute.

The abstract of the ES&T article is available on-line at http://pubs.acs.org/journals/esthag/index.html, under the Articles ASAP tab. Full text for the ES&T article can be obtained from Michael Bernstein, Office of Communications, American Chemical Society, (202)-872-6042 (m_bernstein@acs.org).


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