Despite an increase in vehicle miles traveled (VMT) of 13% from 2002 to 2015 (the latest year for which data are available), the total amount of airborne pollutants emitted from highway vehicles has declined considerably, according to the US Department of Energy (DOE).
|Source: DOE. Click to enlarge.|
Due to improvements in fuels and vehicle technologies, since 2002 highway emissions declined 65% for carbon monoxide (CO); 65% fir nitrogen oxides (NOx); 56% for volatile organic compounds (VOC), and 29% for particulate matter (PM).
In addition to the 13% increase in VMT, the size of the vehicle parc increased 12% as well.
Particulate matter emissions include both fine particle matter less than 10 microns (PM-10) and fine particle matter less than 2.5 microns (PM-2.5). The Environmental Protection Agency updated methodologies for transportation emissions in 2002, so data are not directly comparable to earlier years.