Millions of short tons
| Carbon monoxide | Nitrogen oxides | |||||
|---|---|---|---|---|---|---|
| All sources | Transportation, total | Transportation (percent of total) | All sources | Transportation, total | Transportation (percent of total) | |
| 1998 | 115.38 | 73.24 | 63 | 24.35 | 8.62 | 35 |
| 1999 | 114.54 | 68.71 | 60 | 22.84 | 8.37 | 37 |
| 2000 | 114.47 | 68.06 | 59 | 22.60 | 8.39 | 37 |
| 2001 | 106.26 | 63.48 | 60 | 21.55 | 7.77 | 36 |
| 2002 | 111.06 | 60.60 | 55 | 21.14 | 7.87 | 37 |
| 2003 | 105.08 | 56.58 | 54 | 20.46 | 7.41 | 36 |
| 2004 | 99.04 | 52.56 | 53 | 19.79 | 6.95 | 35 |
| 2005 | 93.03 | 48.54 | 52 | 19.12 | 6.49 | 34 |
| 2006 | 87.92 | 45.32 | 52 | 18.11 | 6.06 | 33 |
| 2007 | 82.80 | 42.09 | 51 | 17.32 | 5.64 | 33 |
| 2008 | 77.69 | 38.87 | 50 | 16.34 | 5.21 | 32 |
| Volatile organic compounds | Sulfur dioxide | |||||
|---|---|---|---|---|---|---|
| All sources | Transportation, total | Transportation (percent of total) | All sources | Transportation, total | Transportation (percent of total) | |
| 1998 | 18.78 | 5.86 | 31 | 18.94 | 0.30 | 2 |
| 1999 | 18.27 | 5.68 | 31 | 17.54 | 0.30 | 2 |
| 2000 | 17.51 | 5.33 | 30 | 16.35 | 0.26 | 2 |
| 2001 | 17.11 | 4.95 | 29 | 15.93 | 0.25 | 2 |
| 2002 | 21.16 | 4.92 | 23 | 14.77 | 0.25 | 2 |
| 2003 | 20.48 | 4.65 | 23 | 14.80 | 0.21 | 1 |
| 2004 | 19.79 | 4.38 | 22 | 14.82 | 0.18 | 1 |
| 2005 | 18.42 | 4.11 | 22 | 14.84 | 0.15 | 1 |
| 2006 | 17.59 | 3.88 | 22 | 13.66 | 0.12 | 1 |
| 2007 | 16.76 | 3.65 | 22 | 13.01 | 0.09 | 1 |
| 2008 | 15.93 | 3.42 | 21 | 11.43 | 0.06 | 1 |
NOTE: Transportation, total data include emissions by highway vehicles only.
SOURCE: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries, available at http://www.epa.gov/ttn/chief/trends/index.html as of November 2009 as cited in U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, National Transportation Statistics, tables 4-40, 4-41, 4-42, and 4-45, available at http://www.bts.gov/publications/national_transportation_statistics/ as of January 2010.