Table 5-11: Estimated National Average Vehicle Emissions Rates of Heavy-duty and Light-duty Vehicles (grams per mile)
Air quality is affected by emissions from freight vehicles. Compared with gasoline fueled cars and trucks, diesel fueled heavy trucks emit small amounts of carbon monoxide (CO) but large amounts of nitrogen oxides (NOx).
Freight transportation is a major source of NOx emissions accounting for 27 percent of all U.S. NOx emissions and half of emissions from mobile sources. Freight transportation also accounts for about one-third of emissions of particulate matter 10 microns in diameter (PM-10) from mobile sources. Most PM-10, however, comes from agricultural fields, wildfires, and fugitive dust. Consequently, freight transportation is a minor factor when considering total PM-10 emissions.
 | 1990 | 2000 | 2001 | 2002 | 2003 | 2004 |
|---|---|---|---|---|---|---|
| Gasoline (assuming zero RFG) | ||||||
| Cars | ||||||
| Exhaust HC | 2.79 | 0.97 | 0.89 | 0.81 | 0.74 | 0.61 |
| Nonexhaust HC | 1.21 | 0.92 | 0.88 | 0.84 | 0.81 | 0.77 |
| Total HC | 3.99 | 1.89 | 1.77 | 1.65 | 1.54 | 1.37 |
| Exhaust CO | 42.89 | 18.53 | 18.03 | 17.58 | 17.13 | 13.79 |
| Exhaust NOx | 2.70 | 1.29 | 1.25 | 1.20 | 1.14 | 1.00 |
| Light trucks | ||||||
| Exhaust HC | 3.68 | 1.45 | 1.35 | 1.24 | 1.13 | 0.96 |
| Nonexhaust HC | 1.36 | 0.97 | 0.94 | 0.89 | 0.84 | 0.80 |
| Total HC | 5.04 | 2.42 | 2.29 | 2.13 | 1.98 | 1.76 |
| Exhaust CO | 56.23 | 26.81 | 25.61 | 24.32 | 22.30 | 18.76 |
| Exhaust NOx | 2.62 | 1.54 | 1.53 | 1.50 | 1.45 | 1.32 |
| Heavy trucks | ||||||
| Exhaust HC | 3.66 | 1.22 | 1.09 | 0.98 | 0.82 | 0.73 |
| Nonexhaust HC | 2.74 | 1.62 | 1.54 | 1.48 | 1.41 | 1.35 |
| Total HC | 6.40 | 2.84 | 2.63 | 2.46 | 2.24 | 2.08 |
| Exhaust CO | 85.61 | 31.08 | 27.59 | 24.73 | 20.60 | 18.46 |
| Exhaust NOx | 7.19 | 5.26 | 5.13 | 5.01 | 4.91 | 4.62 |
| Diesel | ||||||
| Cars | ||||||
| Exhaust HC | 0.68 | 0.80 | 0.76 | 0.73 | 0.73 | 0.60 |
| Exhaust CO | 1.49 | 1.78 | 1.75 | 1.73 | 1.74 | 1.59 |
| Exhaust NOx | 1.83 | 1.81 | 1.72 | 1.62 | 1.54 | 1.43 |
| Light trucks | ||||||
| Exhaust HC | 1.59 | 1.02 | 0.88 | 0.96 | 0.97 | 0.98 |
| Exhaust CO | 2.67 | 1.77 | 1.54 | 1.66 | 1.68 | 1.68 |
| Exhaust NOx | 2.71 | 1.76 | 1.64 | 1.67 | 1.66 | 1.59 |
| Heavy trucks | ||||||
| Exhaust HC | 2.21 | 0.79 | 0.74 | 0.69 | 0.61 | 0.58 |
| Exhaust CO | 10.06 | 4.10 | 3.82 | 3.58 | 3.37 | 3.19 |
| Exhaust NOx | 23.34 | 18.05 | 16.68 | 15.52 | 13.92 | 12.50 |
Key: CO = carbon monoxide; HC = hydrocarbon; NOx = nitrogen oxides; RFG = reformulated gasoline.
Source: U.S. Environmental Protection Agency, National Vehicle and Fuel Emissions Laboratory.
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