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02 Most people know nitrous oxide as laughing gas that dentists use as an anaesthetic. But this is only a minor source of emissions. Deforestation, animal waste and bacterial decomposition of plant material in soils and streamsemituptotwo-thirdsofatmosphericN 2 O.Unlikenatural sources, emissions from human-related processes are steadily increasing, currently boosting the atmospheric concentration of N 2 O by roughly one percent every four years. nitrous oxide the culprits 13

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NITROUS OXIDE: A MAJOR CULPRIT AFTER 2010

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Annual global emissions have been estimated at about 2 000 million tonnes of CO 2 -equivalent and in 2010, the ODP of N 2 O was estimated at 0.017. Now the main threat to the ozone layer, nitrous oxide is also a greenhouse gas. Limiting its emis- sions yields a double benefit. With a global warming potential (GWP) of about 300, N 2 O accounts for almost eight per cent of GHG emissions. Nitrous oxide is not regulated by the Montreal Protocol, but falls under the Kyoto Protocol. An unwanted side effect of the Montreal Protocol in stalling CFC emissions is that N 2 O can now develop its ozone destructive potential more ef- fectively. (See explanation in the graph). Together with the rising concentrations this could slow the ozone layer’s recovery. options for control Because many N 2 O releases are diffuse, limiting them will be much more challenging than simply controlling indus- trial processes. Farming is a growing source of N 2 O emis- sions. Widespread and often poorly controlled use of ani- mal waste as a fertilizer also causes substantial emissions. Applying fertilizer dosages in line with demand and what the soil can absorb significantly reduces N 2 O emissions and at the same time addresses high nitrate levels in drink- ing water supplies and eutrophication in estuaries. Infor- mation campaigns for farmers should focus on the optimal form and timing of fertilizer application. 0267/< 5(/($6(' %< 7+( $*5,&8/785$/ 6(&725 0DQXUH )HUWLOL]HUV ,QGXVWU\ DQG WUDQVSRUW %LRPDVV EXUQLQJ 0LOOLRQ WRQQHV 1LWURXV R[LGH DQWKURSRJHQLF HPLVVLRQV 0HDW FRQVXPSWLRQ JURZWK PRUH PDQXUH SURGXFHG %LRIXHO FURSV DUHD H[WHQVLRQ PRUH IHUWLOL]HUV XVHG 0RUHRYHU 1 HPLVVLRQV LQ WKH DJULFXOWXUDO VHFWRU DUH SURMHFWHG WR LQFUHDVH GXH WR 0 6 5 4 3 2 1 7

Million tonnes Nitrous oxide anthropogenic emissions

N 2 0 emissions in the agricultural sector are projected to increase due to:

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Agriculture represents almost 80 % of all anthropogenic N 2 O emitted

Manure

Biofuel crops area extension (more fertilizers used)

Fertilizers

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Industry and transport Biomass burning

Source: Eric A. Davidson, The contribution of manure and fertilizer nitrogen to atmospheric nitrous oxide since 1860, Nature Geoscience, August 2009. Source: Eric A. Davidson, The contribution of manure and fertilizer nitrogen to atmospheric nitrous oxide since 1860 , Nature Geoscience, August 2009.

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