Table 4-41. Estimated National Emissions of Nitrogen Oxides (Million short tons)

Table 4-41. Estimated National Emissions of Nitrogen Oxides (Million short tons)

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  1970 1975 1980 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
Transportation                                 
On-road vehicles 7.39 8.65 8.62 8.09 7.77 7.65 7.66 7.68 R7.09 R7.47 R7.62 R7.81 R8.08 R7.83 R7.85 R7.88 7.77
Off-road                                 
Aircraft 0.07 0.09 0.11 0.12 0.12 0.13 0.13 0.14 0.16 0.16 0.16 0.16 0.16 0.17 0.17 R0.17 0.17
Railroads 0.50 0.59 0.73 0.81 0.83 0.85 0.90 0.92 0.93 0.93 0.95 0.95 0.95 0.99 0.92 0.95 0.95
Marine vesselsR 0.17 0.21 0.47 0.56 0.60 0.63 0.70 0.75 0.94 1.00 0.96 0.92 0.93 0.94 0.99 1.00 1.01
Other off-roada, R 0.04 0.04 0.04 0.06 0.06 0.07 0.07 0.07 0.08 0.08 0.08 0.08 0.08 0.08 0.09 0.09 0.09
Total transportationR 8.17 9.58 9.97 9.64 9.38 9.33 9.46 9.56 9.20 9.64 9.77 9.92 10.20 10.01 10.02 10.09 9.99
Nontransportation                                 
Fuel combustion 10.06 10.49 11.32 10.05 9.87 R10.01 10.47 10.54 10.89 R10.73 10.93 11.11 11.02 10.83 R10.35 R10.40 10.19
Industrial processesb 0.78 0.54 0.56 0.80 0.79 0.76 0.78 0.77 0.80 0.72 0.76 0.74 0.77 0.77 R0.76 R0.79 0.80
Waste disposal and recycling 0.44 0.16 0.11 0.09 0.09 0.09 0.09 0.08 0.09 0.10 0.10 0.12 0.11 0.10 0.10 0.10 0.10
Miscellaneousc R1.49 R1.88 R2.43 R2.62 R2.68 R2.88 R3.33 R2.94 R3.07 R3.03 R3.05 3.08 R3.29 R3.22 R3.46 R3.46 3.40
Total nontransportation R12.77 R13.07 R14.42 R13.56 R13.43 R13.74 R14.67 R14.33 R14.85 R14.58 R14.84 15.05 R15.19 R14.92 R14.67 R14.75 14.49
TOTAL all sourcesR20.93 22.63 24.38 23.20 22.81 23.07 24.12 23.89 24.05 24.25 24.60 24.96 25.37 24.92 24.68 24.82 24.45

a Other off-road comprises nonroad gasoline- and diesel-powered recreational, airport service and railway maintenance vehicles, and recreational marine vessels.
b Industrial processes comprises chemical and allied product manufacturing, metals processing, petroleum and related industries, and other industrial processes; and solvent  utilization, storage, and transport.
c Miscellaneous comprises nonroad gasoline- and diesel-powered construction, industrial, lawn and garden, farm, light-commercial, logging vehicles, and other non-road sources;  health services, cooling towers, fugitive dust; and other combustion sources that could not be accurately allocated to specific source categories.

KEY: R = revised.

NOTES: The methodologies used to estimate emissions constantly evolve and undergo major changes. These improved methods are often used to revise estimates for previous years. Therefore, some estimates in this table may not match estimates produced in previous reports, and some trends may not be consistent across years in which major methodology changes have occurred.Numbers may not add to totals due to rounding.

SOURCES: U.S. Environmental Protection Agency, National Air Pollutant Emission Trends: 1900-1998 (EPA-454/R-00-002) (Research Triangle Park, NC: March 2000), table A-2; also available at Internet site www.epa.gov/ttn/chief/trends98/emtrnd.html, as of Aug. 8, 2000.