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Latest Findings on National Air Quality : 1999 Status and Trends

By Environmental Protection Agency

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Book Id: WPLBN0000145882
Format Type: PDF eBook
File Size: 2.8 MB
Reproduction Date: 2007
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Title: Latest Findings on National Air Quality : 1999 Status and Trends  
Author: Environmental Protection Agency
Language: English
Subject: Ecology, Natural resource issues, Environemtal protection
Collections: Environmental Awareness Library Collection
Publication Date:
Publisher: United States Environmental Protection Agency


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Agency, E. P. (n.d.). Latest Findings on National Air Quality : 1999 Status and Trends. Retrieved from

Excerpt: Highlights: -- Overall, national air quality levels measured at thousands of monitoring stations across the country have shown improvement over the past 20 years for all six principal pollutants. Despite this progress, over 150 million tons of air pollution were released into the air in 1999 in the United States, and approximately 62 million people lived in counties where monitored data showed unhealthy air for one or more of the six principal pollutants. While the national trends continue to improve, air quality trends for some areas, including rural locations, have actually worsened. Some national parks, including the Great Smoky Mountains and Shenandoah, have high air pollution concentrations resulting from the transport of pollutants many miles from their original sources. In 1999, for the second consecutive year, average rural 1-hour ozone (smog) levels were greater than the average levels observed for urban sites. Between 1900 and 1970, emissions of the six principal pollutants increased significantly. For example, estimated emissions of nitrogen oxides (NOx) increased 690 percent, volatile organic compounds increased 260 percent, and sulfur dioxide increased 210 percent. Without the pollution controls resulting from amendments to the Clean Air Act, emissions would have continued to increase at a higher rate. Since the 1970 Clean Air Act was signed into law, emissions of each of the six pollutants decreased, with the exception of NOx. Between 1970 and 1999, emissions of NOx increased 17 percent. The majority of this increase can be attributed to heavy-duty diesel vehicles and coal-fired power plants. EPA has major initiatives to reduce emissions of NOx considerably from these sources. Emissions of NOx contribute to the formation of ground-level ozone (smog), acid rain, and other environmental problems, even after being carried by the wind hundreds of miles from their original source. Estimates of nationwide air toxic emissions have dropped approximately 23 percent between 1990 and 1996. For example, perchloroethylene monitored in 16 urban sites in California showed a drop of 60 percent from 1989 to 1998. Benzene is another widely monitored toxic air pollutant. It is emitted from cars, trucks, oil refineries, and chemical processes. Measurements taken from 84 urban monitoring sites around the country show a 39-percent drop in benzene levels from 1993 to 1998.

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