NOTES: Revisions to previous estimates are all related to the development of the 1999 National Emissions Inventory (NEI). The 1999 estimates in the table are taken from Version 2 of the 1999 NEI and reflect many new data submissions from state and local air management agencies. The 1999 emissions estimates from mobile sources are in most cases based on the new MOBILE6 and the draft NONROAD2002 emissions models. This is the first time that estimates using these models have appeared in this format. Some but relatively few mobile source estimates were provided by state air agencies. The largest set of state-submitted data in 1999 was from California. Estimates for mobile sources for years prior to 1999 were made consistent with the estimates for 1999 and later, allowing for a generally consistent time trend except that state-submitted data were incorporated for 1999 only. See the tables in appendix B for definitions of "highway" and "other" vehicles.
SOURCE: U.S. Environmental Protection Agency (EPA), Office of Air Quality Planning and Standards, National Emissions Inventory, Air Pollutant Emission Trends, available at http://www.epa.gov/ttn/chief/trends/index.html/, as of August 2003.