Indices are calculated using data on highway vehicle emissions only. Particulate matters include PM without condensibles.
Key: PM-10 = airborne particulates of less than 10 microns; PM-2.5 = airborne particulates of less than 2.5 microns.
As cited in U.S. Department of Transportation, Bureau of Transportation Statistics, National Transportation Statistics, tables 4-45 through 4-50, available at https://www.bts.gov/.
Last Updated: May 2018