Precipitation in Northeast, Midwest Contains Nitrate from Distant Industrial Facilities

Rain and snow in rural areas of the Northeastern and Midwestern United States contain nitrate that has been traced to power plants and other industrial facilities hundreds of miles away, according to a new U.S. Geological Survey (USGS) study.

Although vehicles are the single largest emission source of nitrogen oxides in the Northeast and Midwest, distant stationary sources may have a greater impact on nitrate found in rain and snow, USGS officials stated.

"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 eight years," said Emily Elliott, former USGS scientist and current assistant professor at the University of Pittsburgh.

The study, published recently on the Web site of the journal Environmental Science & Technology, is 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.

"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," Elliott said.

The abstract of the Environmental Science & Technology article can be accessed at, under the "Articles ASAP" tab.

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