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NOAA image of the Ohio River Valley, which showed a decline in nitrogen dioxide.Dec. 8, 2006 A major smog-forming pollutant is declining over the eastern United States, according to a new study by scientists at NOAA and the University of Bremen, Germany. New satellite observations mark the first time space-based instruments have detected the regional impact of pollution controls implemented by coal-burning electric power plants in the 1990s. The findings were published this month in Geophysical Research Letters, a publication of the American Geophysical Union. (Click NOAA image for larger view of the Ohio River Valley, which showed a decline in nitrogen dioxide. Click here for high resolution version of three graphics. Please credit “NOAA.”)

High-precision instruments aboard European satellites have detected a 38 percent decline in nitrogen dioxide in the Ohio River Valley and nearby states between 1999 and 2005, according to the study. Nitrogen dioxide (NO2) and nitric oxide (NO) are two gases that form a group of pollutants known as nitrogen oxides (NOx), which are created primarily through fossil fuel burning. When combined with other gases and sunlight, they form ozone, the major urban air pollutant in smog. Ground-level ozone harms human health and vegetation and is a key pollutant targeted by the U.S. Environmental Protection Agency.

NOAA aerial image of the Ghent Power Plant, in Ghent, Ky., taken aboard a NOAA hurricane hunter aircraft during the 1999 Southern Oxidants Study."The reduction in NOx emissions from these large eastern power plants is dramatic," says Greg Frost, an author of the study and a scientist in the NOAA Earth System Research Lab and the Cooperative Institute for Research in the Environmental Sciences, both in Boulder, Colo. "With these new data, model results predict lower ozone pollution across much of the eastern United States." The next step is to confirm through observations and further analysis that ozone is actually declining, adds Si-Wan Kim, also of ESRL and CIRES and lead author of the study. Kim and Frost are atmospheric scientists in ESRL's Chemical Sciences Division. (Click NOAA aerial image for larger view of the Ghent Power Plant, in Ghent, Ky., taken aboard a NOAA hurricane hunter aircraft during the 1999 Southern Oxidants Study. Click here for high resolution version. Please credit “NOAA.”)

"NOAA scientists and their colleagues have provided an objective assessment of the positive impact on Earth's atmosphere of actions taken by industry with the ultimate goal to improve air quality over the eastern United States," said Richard W. Spinrad, Ph.D., assistant administrator of NOAA Research. "This work is an excellent example of NOAA's value to society as an objective science broker."

Computer model results show the nitrogen oxide emission reductions should decrease ozone levels in the six states of the Ohio River Valley (Illinois, Indiana, Ohio, Pennsylvania, Kentucky and West Virginia), as well as North Carolina, Virginia, Georgia and Texas.

Home to many large electric power plants, the Ohio River Valley produced a third of all U.S. nitrogen oxide emissions from power plants during the 1990s. The region's nitrogen oxide emissions drift downwind, producing ozone in urban areas hundreds of miles away and hindering their compliance with EPA standards, especially in the Northeast. In response, the EPA mandated reductions of stationary sources of nitrogen oxide emissions, primarily eastern U.S. coal-fired power plants.

After implementing pollution controls, utility companies reported a 45 percent decline in nitrogen oxide emissions from individual power plants in 2004 compared to 1990 levels, even though electricity production increased during this period. The NOAA study is the first to verify from space that these single-point reductions have had a measurable impact on the atmosphere across the entire region.

The authors report much smaller decreases in satellite measurements of atmospheric nitrogen dioxide in the northeastern states, where the primary source is fossil fuel combustion in cars and other vehicles. The highest nitrogen dioxide levels occurred in areas with combined urban, industrial and power plant sources, such as the northeast urban corridor, Chicago, Pittsburgh, Detroit, Toronto, Atlanta, Dallas and Houston.

In 2007 NOAA, an agency of the U.S. Commerce Department, celebrates 200 years of science and service to the nation. Starting with the establishment of the U.S. Coast and Geodetic Survey in 1807 by Thomas Jefferson much of America's scientific heritage is rooted in NOAA. The agency is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and information service delivery for transportation, and by providing environmental stewardship of the nation's coastal and marine resources. Through the emerging Global Earth Observation System of Systems (GEOSS), NOAA is working with its federal partners, more than 60 countries and the European Commission to develop a global monitoring network that is as integrated as the planet it observes, predicts and protects.

Relevant Web Sites
NOAA Earth System Research Lab

NOAA Chemical Sciences Division


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