Agriculture is the most important N₂O emission source in 2009 contributing 91.2 % of which N₂O from agricultural soils accounts for 84.1 %. N₂O is emitted as a result of microbial processes in the soil. Substantial emissions also come from drainage water and coastal waters where nitrogen is converted to N₂O through bacterial processes. However, the nitrogen converted in these processes originates mainly from the agricultural use of manure and nitrogen fertilisers. The main reason for the drop in the emissions of N₂O in the agricultural sector of 32.4 % from 1990 to 2009 is legislation to improve the utilisation of nitrogen in manure. The legislation has resulted in less nitrogen excreted pr unit of livestock produced and a considerable reduction in the use of nitrogen fertilisers. The basis for the N₂O emission is then reduced. Combustion of fossil fuels in the energy sector, both stationary and mobile sources, contributes 6.2 %. The N₂O emission from transport contributes by 2.4 % in 2009. This emission has increased during the nineties because of the increase in the use of catalyst cars. Production of nitric acid stopped in 2004 and the emissions from industrial processes is therefore not occurring from 2005 onwards. The sector Solvent and Other Product Use covers N₂O from e.g. anaesthesia.

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