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Transportation Air Quality Facts and Figures January 2006

Emissions Trends

Percent of Change in Emissions

1970-2002

Percent of Change in Emissions 1970-2002. Click image for source data.

Americans have made great progress in cleaning the air. For nearly three decades, national emissions trends for point and area sources and on-road sources have been declining. A great deal of the credit for the improvements in on-road sources goes to cleaner cars and trucks, and reformulated fuels. Meanwhile, emissions from non-road engines have increased.

VOC Emissions

1970-2002

VOC Emissions 1970-2002. Click image for source data.

Volatile organic compounds (VOC) are precursors of ground-level ozone. In 2002, on-road vehicles produced 27 percent of all VOC emissions, down from 49 percent in 1970. On-road vehicle emissions are down 73 percent since 1970.

VOC Emissions

2002

VOC Emissions 2002. Click image for source data.

Source: U.S. Environmental Protection Agency, Office of Air and Radiation.
2002 Air Quality Trends Summary Report. January 2005.

NOx Emissions 1970-2002

NOX Emissions 10970-2002. Click image for source data.

In addition to VOC, oxides of nitrogen (NOx) contribute to the formation of ozone. In 2002, on-road vehicles produced 35 percent of all NOx emissions, down from 47 percent in 1970. On-road vehicle emissions of NOx are down 41 percent since 1970.

NOx Emissions 2002

NOX Emissions 2002. Click image for source data.

Source: U.S. Environmental Protection Agency, Office of Air and Radiation.
2002 Air Quality Trends Summary Report. January 2005.

Change in NOx Emissions by Vehicle Class 1970-2002

Change in NOX Emissions by Vehicle Class 1970-2002. Click image for source data.

Between 1970 and 2002, NOx emissions from passenger vehicles, light-duty trucks, and heavy-duty gas vehicles decreased by 75, 9, and 44 percent, respectively. By contrast, NOx emissions from heavy-duty diesel vehicles increased more than 90 percent.

Source: U.S. Environmental Protection Agency, Office of Air and Radiation. 2002 Air Quality Trends Summary Report. January 2005.

CO Emissions 1970-2002

CO Emissions 1970-2002. Click image for source data.

On-road vehicles are the largest source of carbon monoxide (CO) emissions. In 2002, on-road vehicles produced 56 percent of all CO emissions, down from 80 percent in 1970.

Source: U.S. Environmental Protection Agency, Office of Air and Radiation. 2002 Air Quality Trends Summary Report. January 2005.

CO Emissions 2002

CO Emissions 2002. Click image for source data.

Source: U.S. Environmental Protection Agency, Office of Air and Radiation. 2002 Air Quality Trends Summary Report. January 2005.

PM10 Emissions 1985-2002

PM10 Emissions 1985-2002. Click image for source data.

Particulate matter consists of dust, direct smoke, and liquid droplets. Traditionally inventoried sources, such as fuel combustion, industrial sources, and transportation, together make up only about 15 percent of total PM10 emissions. PM10 from all sources declined over 45 percent between 1985 and 2002, and on-road vehicle emissions decreased over 50 percent.

PM10 Emissions 2002

PM10 Emissions 2002. Click image for source data.

The majority of PM10 emissions come from sources that are not traditionally inventoried, such as fugitive dust from paved and unpaved roads, construction and agriculture.

Source: U.S. Environmental Protection Agency, Office of Air and Radiation. 2002 Air Quality Trends Summary Report. January 2005. Note: 1970-1998 emissions do not include condensibles.

PM2.5 Emissions 1990-2002

PM2.5 Emissions 1990-2002. Click image for source data.

Fine particulate matter, PM2.5, results from motor vehicle fuel combustion and other sources. Since 1990, PM2.5 from all sources decreased by almost 10 percent, and on-road vehicle emission declined more than 59 percent.

PM2.5 Emissions 2002

PM2.5 Emissions 2002. Click image for source data.

The majority of PM2.5 emissions come from sources that are not traditionally inventoried. On-road exhaust, and emissions from brake and tire wear accounted for only 2 percent of the direct PM2.5 emissions in 2002. Fugitive dust from vehicles traveling on paved and unpaved roads account for 26 percent of PM2.5 emissions.

Source: U.S. Environmental Protection Agency, Office of Air and Radiation. 2002 Air Quality Trends Summary Report. January 2005.

Note: 1970-1998 emissions do not include condensibles. Condensibles are the majority of PM2.5 that is formed in the atmosphere from 'precursor' gases such as SO2 and NOx.

Updated: 07/06/2011
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