Nitrogen dioxide is a criteria pollutant under the Clean Air Act. Accordingly, nitrogen oxide emissions are considered a major environmental concern. Most NOx emissions result from fossil fuel combustion. Mobile sources of combustion, mainly motor vehicles and aircraft, contributed about 45 perfect of total 1980 NOx emissions nationwide.
U.S. Environmental Protection Agency. 1986. Nitrogen Oxide Control for Stationary Combustion Sources. Office of Research and Development - U.S. Environmental Protection Agency