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Transportation Air Quality Selected Facts and Figures

Emissions Trends

How Have VOC Emissions Changed since 1990?

VOC Emissions (2013)

Title: Pie chart showing the sources of volatile organic compounds (VOC) emissions in 2013 - Description: The pie chart shows that in 2013, 14% of VOC emissions were from on-road vehicles, 11% were from non-road vehicles, 4% were from stationary fuel combustion, 41% were from industrial and other processes, and 30% were from miscellaneous sources.

VOCs are precursors of ground-level ozone and PM. In 2013, on-road vehicles produced 14 percent of all VOC emissions, down from 39 percent in 1990. On-road vehicle VOC emissions have decreased 77 percent in the last two decades.

VOC Emissions Trends since 1990

Title: Line chart showing trends in total and on-road vehicle volatile organic compounds (VOC) emissions from 1990 to 2013 in millions short tons - Description: The line chart shows two lines - one for Total VOC emissions and one for VOC emissions from on-road vehicles, in units of million short tons. The On-road Vehicles line starts at almost 10 in 1990 and declines in a basically linear fashion to approximately 2 in 2013. The Total line starts at approximately 24 in 1990, decreases in a basically linear fashion until approximately 17.5 in 2001, jumps up to 20 in 2002, decreases steadily to approximately 17 in 2005, and remains basically flat through 2013.

Source: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries, https://www.epa.gov/air-emissions-inventories/air-pollutant-emissions-trends-data

How Have NOX Emissions Changed since 1990?

NOX Emissions (2013)

The pie chart shows that in 2013, 38% of NOx emissions were from on-road vehicles, 21% were from non-road vehicles, 28% were from stationary fuel combustion, 10% were from industrial and other processes, and 3% were from miscellaneous sources.

In combination with VOCs, NOx contributes to the formation of ozone. It is also a precursor to PM. In 2013, on-road vehicles produced 38 percent of all NOx emissions, the same as in 1990. However, total on-road vehicle emissions of NOx have decreased 48 percent since 1990.

NOx Emissions Trends since 1990

The line chart shows two lines - one for Total NOx emissions and one for NOx emissions from on-road vehicles, in units of million short tons. The On-road Vehicles line starts at almost 10 in 1990, declines in a basically linear fashion to approximately 8 in 2001, jumps up to 10 in 2001, and decreases steadily to 5 in 2013. The Total line starts just above 25 in 1990, remains basically flat until 1998, drops to approximately 21 by 2001, jumps up to almost 25 in 2002, and decreases linearly to approximately 13 by 2013.

Source: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries, http://www3.epa.gov/ttn/chief/trends/index.html

How Have CO Emissions Changed since 1990?

CO Emissions (2013)

Title: Pie chart showing the sources of carbon monoxide (CO) emissions by percentage in 2013 - Description: The pie chart shows that in 2013, 34% of CO emissions were from on-road vehicles, 21% were from non-road vehicles, 7% were from stationary fuel combustion, 4% were from industrial and other processes, and 34% were from miscellaneous sources.

On-road vehicles are one of the largest sources of CO emissions. However, by 2013, on-road vehicles produced 34 percent of all CO emissions, down from 72 percent in 1990.

CO Emissions Trends since 1990

Title: Line chart showing trends in total and on-road vehicle carbon monoxide (CO) emissions from 1990 to 2013 in millions short tons - Description: The line chart shows two lines - one for Total CO emissions and one for CO emissions from on-road vehicles, in units of million short tons. The On-road Vehicles line starts at approximately 110 in 1990, declines in a basically linear fashion to just above 60 in 2001, drops sharper to 50 in 2002, and decreases steadily to approximately 25 in 2013. The Total line starts at approximately 150 in 1990, declines in a basically linear fashion to approximately 75 in 2009, and remains relatively flat through 2013.

Source: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries, https://www.epa.gov/air-emissions-inventories/air-pollutant-emissions-trends-data

How Have PM10 Emissions Changed since 1990?

PM10 consists of dust, direct smoke, and liquid droplets. The majority of PM10 emissions come from sources such as prescribed fires and wildfires, dust from paved and unpaved roads, road construction, and agriculture operations (designated Miscellaneous in the pie chart below). Sources such as fuel combustion, industrial sources, and transportation, together make up only 13 percent of total PM10 emissions.

PM10 Emissions (2013)

Title: Pie chart showing sources of PM-10 emissions by percentage in 2013 - Description: The pie chart shows that in 2013, 2% of PM-10 emissions were from on-road vehicles, 1% were from non-road vehicles, 5% were from stationary fuel combustion, 6% were from industrial and other processes, and 87% were from miscellaneous sources.

PM10 from all sources declined over 23 percent between 1990 and 2013, and on- road vehicle PM10 emissions decreased over 31 percent.

PM10 Emissions Trends since 1990

Title: Line chart showing trends in total and on-road vehicle particulate matter of 10 microns or less (PM-10) emissions from 1990 to 2013 in millions short tons - Description: The line chart shows two lines - one for Total PM-10 emissions and one for PM-10 emissions from on-road vehicles, in units of million short tons. The On-road Vehicles line starts at approximately 0.5 in 1990 and declines in a basically linear fashion to a little above 0 in 2013. The Total line starts at approximately 28 in 1990, remains basically flat through 1993, drops to about 23 by 1996, increases slowly to almost 25 by 2001, drops to approximately 22 in 2002, and remains relatively flat through 2013.

Source: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries, https://www.epa.gov/air-emissions-inventories/air-pollutant-emissions-trends-data

How Have PM2.5 Emissions Changed since 1990?

PM2.5 results from motor vehicle fuel combustion and other sources. Most PM2.5 emissions come from sources such as prescribed fires and wildfires, dust from paved and unpaved roads, road construction, and agriculture operations (designated Miscellaneous in the pie chart below). Sources such as fuel combustion, industrial sources, and transportation, together make up 29 percent of total PM2.5 emissions.

PM2.5 Emissions (2013)

Title: Pie chart showing sources of PM-2.5 emissions by percentage in 2013 - Description: The pie chart shows that in 2013, 3% of PM-2.5 emissions were from on-road vehicles, 3% were from non-road vehicles, 14% were from stationary fuel combustion, 9% were from industrial and other processes, and 71% were from miscellaneous sources.

Since 1990, PM2.5 from all sources decreased by almost 17 percent. Although on- road exhaust and emissions from brake and tire wear accounted for only 3 percent of the direct PM2.5 emissions in 2013, on-road vehicle PM2.5 emissions declined more than 43 percent since 1990.

PM2.5 Emissions Trends since 1990

Title: Line chart showing trends in total and on-road vehicle particulate matter of 2.5 microns or less (PM-2.5) emissions from 1990 to 2013 in millions short tons - Description: The line chart shows two lines - one for Total PM-2.5 emissions and one for PM-2.5 emissions from on-road vehicles, in units of million short tons. The On-road Vehicles line starts slightly below 0.5 in 1990 and declines in a basically linear fashion to a little above 0 in 2013. The Total line starts a little below 8 in 1990, declines basically linearly to just above 6 in 1998, jumps to approximately 7 in 1999, stays basically flat through 2001, drops to just below 6 in 2002, and increases slowly to just above 6 by 2013.

Source: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries, https://www.epa.gov/air-emissions-inventories/air-pollutant-emissions-trends-data

Note: 1990–1998 emissions do not include condensables. Condensables are the majority of PM2.5 that is formed in the atmosphere from precursor gases such as SO2 and NOx.

How Have Emissions Changed in the Last 30 Years?

America made great progress cleaning the air. For nearly 30 years, national emissions trends for point and area sources and on-road sources have declined. However, non-road source emissions increased with the exception of PM10.

Title: Bar graphs showing percent change in VOC, NOx, PM-10, and CO emissions by source from 1980 to 2013 (PM-10 is from 1990-2013) - Description: The VOC bar graph shows the percent change in emissions by point and area, on-road, and non-road sources between 1980 and 2013. Point and area source VOC emissions have a decrease of approximately 50 percent, on-road sources have a decrease of 77 percent, and non-road source VOC emissions have an increase of 23 percent. The NOx bar graph shows the percent change in emissions by point and area, on-road, and non-road sources between 1980 and 2013. Point and area source NOx emissions have a decrease of approximately 60 percent, on-road sources have a decrease of 63 percent, and non-road source NOx emissions have an increase of about 7 percent. The PM-10 bar graph shows the percent change in emissions by point and area, on-road, and non-road sources between 1990 and 2013. Point and area source PM-10 emissions have a decrease of approximately 18 percent, on-road sources have a decrease of 20 percent, and non-road source PM-10 emissions have a decrease of 40 percent. The CO bar graph shows the percent change in emissions by point and area, on-road, and non-road sources between 1980 and 2013. Point and area source CO emissions have a decrease of approximately 67 percent, on-road sources have a decrease of 82 percent, and non-road source CO emissions have an increase of 25 percent.

Source: U.S. EPA Office of Air and Radiation, https://www3.epa.gov/airtrends/index.html Note: Data for PM10 begins in 1990.

What has Caused the Improvement?

A great deal of the credit for the improvements in on-road sources goes to cleaner cars and trucks, and fuels.

Updated: 5/3/2016
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