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On-road Sources
Regulatory and voluntary control programs have steadily decreased on-road vehicle emissions since the 1970s. The graphs below show the impact of controls on on-road vehicle emissions of carbon monoxide, hydrocarbons, nitrogen oxides, and particulate matter. On-road vehicles include cars, vans, trucks, motorcycles, and buses. In these graphs, "actual" means as things actually are, with an array of control programs in place. "Without controls" presents a hypothetical picture of what emissions would have been without emission control programs.
Carbon Monoxide
On-road carbon monoxide emissions are less than half what they were in 1970. Actual emissions today are five times less than they would have been without controls implemented since 1970. By 2020, on-road carbon monoxide emissions will be about 20 times less than they would have been without controls in place.
Hydrocarbons
On-road hydrocarbon emissions are about one-third what they were in 1970. Actual emissions today are about 10 times less than they would have been without controls implemented since 1970. By 2020, on-road hydrocarbon emissions will be about 50 times less than they would have been without controls in place.
Nitrogen Oxides
On-road emissions of nitrogen oxides are greater than they were in 1970. This is because growth in vehicle travel has increased faster than our progress in controlling these pollutants. Nonetheless, emissions today are less than half of what they would have been without controls implemented since 1970. By 2020, new emission controls just now starting to take effect are expected to have a major impact. EPA expects on-road nitrogen oxide emissions to be less in 2020 than they were in 1970, and about 20 times less than they would have been without controls in place.
Fine Particulate Matter
On-road emissions of fine particulate matter are just over half what they were in 1970. Actual emissions today are about five times less than they would have been without controls implemented since 1970. By 2020, on-road particulate matter emissions will be about 10 times less than they would have been without controls in place.