Nitrous oxide (dinitrogen monoxide) has significant global warming potential as a greenhouse gas. On a per-molecule basis, considered over a 100-year period, nitrous oxide has 265 times the atmospheric heat-trapping ability of carbon dioxide (CO2). However, because of its low concentration (less than 1/1,000 of that of CO2), its contribution to the greenhouse effect is less than one third that of carbon dioxide, and also less than water vapour and methane. On the other hand, since 38% or more of the N2O entering the atmosphere is the result of human activity, control of nitrous oxide is considered part of efforts to curb greenhouse gas emissions.
Nitrous oxide is released into the atmosphere through agriculture, when farmers add nitrogen-based fertilizers onto the fields, through the breakdown of animal manure. Approximately 79 percent of all nitrous oxide released in the United States came from nitrogen fertilization. Nitrous oxide is also released as a by-product of burning fossil fuel, though the amount released depends on which fuel was used. It is also emitted through the manufacture of nitric acid, which is used in the synthesis of nitrogen fertilizers. The production of adipic acid, a precursor to nylon and other synthetic clothing fibres, also releases nitrous oxide. The total amount of nitrous oxide released that is of human origins is about 40 percent.
Nitrous oxide has also been implicated in thinning the ozone layer. A 2009 study suggested that N2O emission was the single most important ozone-depleting emission and it was expected to remain the largest throughout the 21st century.
