Nitrous oxide (N20) is generated by processes of nitrification and denitrification of the soil and from fossil fuel combustion. Confusingly nitrogen oxides released into the atmosphere at low levels creates ozone and contributes to global warming, but when released into the stratosphere depletes ozone and thus contributes to global warming.
N2O in the atmosphere is currently increasing at a rate of around 0.2-0.3% per year for reasons which are still poorly understood. The increase in 1992 (0.16 percent) was similar in magnitude to annual growth rates between 1977 and 1985, but lower than those observed more recently between 1985 and mid-1991 (0.3 percent/year).
Emissions of N2O in Canada in 1990 were estimated at 92 kilotonnes. Fossil fuel combustion accounted for about 52% of the total, followed by industrial processes (36%), and fertilizer use (12%).
Nitrous oxide is not controlled in the USA as the clean air act in the USA was written in 1970 to control smog, not global warming.The agreement at the Kyoto Climate Convention in December 1997 to reduce emissions believed to cause global warming has not been ratified by the US senate and no implementing rules have been written.