Transportation Air Quality - Selected Facts and Figures
Emission Trends
Percent of Change in Emissions (1970-99)
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Americans have made great progress in cleaning the air. For nearly three decades, national emission trends have been declining. A great deal of credit for the improvements goes to cleaner cars and trucks and reformulated fuels.
*Note: 1985-99.
Source: U.S. Environmental Protection Agency. Office of Air Quality Planning and Standards. National Air Quality Emissions Trends, 1990-1999. March 2001. Tables A-2, A-4, A-5 and A-6.
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VOC Emissions (1970-99)
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Change in Total VOC Emissions: -41%
Change in On-road vehicle VOC Emissions: -59%
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Volatile organic compounds (VOC) are precursors of ground-level ozone. Since all organic compounds contain carbon, volatile organic compounds are often called hydrocarbons (HC). In 1999, on-road vehicles produced 29 percent of all VOC emissions, down from 42 percent in 1970. Point and area sources made up 49 percent of VOC emissions, while non-road engines made up 18 percent and miscellaneous sources made up 4 percent. On-road vehicle emissions of VOC are down 59 percent since 1970. Meanwhile, point and area sources are down 41 percent and miscellaneous sources are down 35 percent. VOC emissions from non-road engines and vehicles rose by 72 percent during this time period.
VOC Emissions 1999
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Source: U.S. Environmental Protection Agency: Office of Air Quality Planning and Standards. National Air Pollution Emission Trends, 1900-1999. March 2001.
NOx Emissions (1970-99)
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Change in Total NOx Emissions: 21%
Change in On-Road Vehicle NOx Emissions: 16% |
In addition to VOC, oxides of nitrogen (NOx) contribute to the formation of ozone. In 1999, on-road vehicles produced 34 percent of all NOx emissions, down slightly from 35 percent in 1970. Point and area sources made up 43 percent of NOx emissions, while non-road engines made up 22 percent and miscellaneous sources made up 1 percent. On-road vehicle emissions of NOx are up 16 percent since 1970, due primarily to the growth in heavy duty diesel engines, where VMT increases have outpaced emissions control technology to effect a net increase in emissions from these vehicles. Meanwhile, point and area sources are down 4 percent since 1970 and non-road engines are up 186 percent.
Source: U.S. Environmental Protection Agency. Office of Air Quality Planning and Standards. National Air Quality Emissions Trends, 1990-1999. March 2001.
NOx Emissions (1999)
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Change in NOx Emissions by Vehicle Class (1970-99)
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Between 1970 and 1999, NOX emissions from passenger vehicles decreased 31 percent. By contrast, NOX emissions from light- and heavy-duty gasoline and diesel vehicles increased 28 percent, 65 percent and 116 percent, respectively. As reported above, total on-road NOx emissions have increased 16 percent.
Source: U.S. Environmental Protection Agency. Current Emissions Trends Summaries: Annual Average Emissions, All Criteria Pollutants (PDF), years including 1970, 1975, 1980, 1985, 1989, 1990-1999. 13 June 2001. (3 October 2001).
- Emission Trends Continued -
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