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Transportation Air Quality Selected Facts and Figures

Air Quality Trends

How Much Progress Is Being Made?

As on-road air pollutant emissions decline over time, air quality improves. Reductions in air pollutant concentrations are impressive, with concentrations of CO decreasing by 60 percent since 2000. All criteria pollutants have shown significant decreases over the last decade, showing a steady trend of improvement.

On-Road Air Pollution Concentration Reductions (2000–2013)

Title: Bar graph showing reductions in five on-road air pollutants between 2000 and 2013 by percent change - Description: The bar graph shows the percent change in on-road source pollutants since 2000. The pollutants shown are CO, NOx, ozone, PM-10, and PM-2.5. The chart indicates a decrease for all five pollutants, CO by 60 percent, NOx by 29 percent, ozone by 18 percent, PM-10 by 30 percent, and PM-2.5 by 34 percent.

Sources: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries,

Updated: 5/3/2016
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