Editing Nitrous oxide (section)

==Atmospheric occurrence==
[[File:N2O mm.png|thumb|upright=1.2|Nitrous oxide (N<sub>2</sub>O) measured by the Advanced Global Atmospheric Gases Experiment ([http://agage.mit.edu/ AGAGE]) in the lower atmosphere ([[troposphere]]) at stations around the world. Abundances are given as pollution free monthly mean mole fractions in [[Parts-per notation|parts-per-billion]].]]
[[File:HATS Nitrous Oxide concentration.png|thumb|right|Nitrous oxide atmospheric concentration since 1978]]
[[File:HATS Nitrous Oxide growth rate.png|thumb|right|Annual growth rate of atmospheric nitrous oxide since 2000]]
[[File:Global Nitrous Oxide Budget 2020.png|thumb|Earth's nitrous oxide budget from the [[Global Carbon Project]] (2020)<ref>{{cite web |url=https://www.globalcarbonproject.org/nitrousoxidebudget/index.htm |title={{chem|N|2|O}} Budget |publisher=Global Carbon Project |access-date=2020-11-09}}</ref>]]
Nitrous oxide is a [[Atmospheric chemistry#Atmospheric composition|minor component of Earth's atmosphere]] and is an active part of the planetary [[nitrogen cycle]].  Based on analysis of air samples gathered from sites around the world, its [[concentration]] surpassed 330&nbsp;[[Parts-per notation|ppb]] in 2017.<ref name="agage">{{cite web |url=https://agage2.eas.gatech.edu/data_archive/data_figures/monthly/pdf/N2O_mm.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://agage2.eas.gatech.edu/data_archive/data_figures/monthly/pdf/N2O_mm.pdf |archive-date=2022-10-09 |url-status=live |title=Nitrous Oxide (N2O) Mole Fraction |publisher=Massachusetts Institute of Technology |access-date=2021-02-15}}</ref> The growth rate of about 1&nbsp;ppb per year has also accelerated during recent decades.<ref name="noaaesrl">{{cite web |url=https://www.esrl.noaa.gov/gmd/ccgg/trends_n2o/ |title=Trends in Atmospheric Nitrous Oxide |publisher=National Oceanic and Atmospheric Administration / Earth System Research Laboratories |access-date=2021-02-15}}</ref>  Nitrous oxide's atmospheric abundance has grown more than 20% from a base level of about 270&nbsp;ppb in 1750.<ref name="tar">{{cite book |url=https://www.ipcc.ch/report/ar3/wg1/|contribution= Chapter 6 |title=TAR Climate Change 2001: The Scientific Basis |page=358}}</ref>
Important atmospheric properties of {{chem|N|2|O}} are summarized in the following table:
{| class="wikitable"
! Property
! Value
|-
| [[Ozone depletion potential]] (ODP)
| 0.017<ref name=Ravishankara>{{Citation|url=https://www.sciencemag.org/content/suppl/2009/08/27/1176985.DC1/Ravishankara.SOM.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.sciencemag.org/content/suppl/2009/08/27/1176985.DC1/Ravishankara.SOM.pdf |archive-date=2022-10-09 |url-status=live|title=Supporting Online Material for - Nitrous Oxide (N<sub>2</sub>O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century|last1=Ravishankara|first1=A. R.|last2=Daniel|first2=John S.|last3=Portmann|first3=Robert W.|date=2009-08-27|journal= Science |volume=326|issue=5949|pages=123–125|doi=10.1126/science.1176985|pmid=19713491|bibcode=2009Sci...326..123R|s2cid=2100618}}</ref> ([[Trichlorofluoromethane|CCl<sub>3</sub>F]] = 1)
|-
| [[Global warming potential]] (GWP: 100-year)
| 273<ref name="ar5">{{cite book |url=https://www.epa.gov/ghgemissions/understanding-global-warming-potentials |title=US Environmental Protection Agency |date=12 January 2016 |page= |language=English |contribution=}}</ref> ([[Carbon dioxide|CO<sub>2</sub>]] = 1)
|-
| [[Greenhouse gas#Atmospheric lifetime|Atmospheric lifetime]]
| 116 ± 9 years<ref name="ar6"/>
|-
|}

In 2022 the IPCC reported that: "The human perturbation of the natural nitrogen cycle through the use of synthetic fertilizers and manure, as well as nitrogen deposition resulting from land-based agriculture and fossil fuel burning has been the largest driver of the increase in atmospheric N2O of 31.0 ± 0.5 ppb (10%) between 1980 and 2019."<ref name="ar6">{{Cite report |title=Chapter 5: Global Carbon and other Biogeochemical Cycles and Feedbacks |url=https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-5/ |access-date=2023-05-06 |website=www.ipcc.ch |language=en}}</ref>

===Emissions by source===
17.0 (12.2 to 23.5) million tonnes total annual average nitrogen in {{chem|N|2|O}} was emitted in 2007–2016.<ref name="ar6"/> About 40% of {{chem|N|2|O}} emissions are from humans and the rest are part of the natural [[nitrogen cycle]].<ref>{{Cite web |last=US EPA |first=OAR |date=2015-12-23 |title=Overview of Greenhouse Gases |url=https://www.epa.gov/ghgemissions/overview-greenhouse-gases |access-date=2023-05-04 |website=www.epa.gov |language=en}}</ref> The {{chem|N|2|O}} emitted each year by humans has a greenhouse effect equivalent to about 3 billion tonnes of carbon dioxide: for comparison humans emitted 37 billion tonnes of actual carbon dioxide in 2019, and methane equivalent to 9 billion tonnes of carbon dioxide.<ref>{{Cite web |title={{!}} Greenhouse Gas (GHG) Emissions {{!}} Climate Watch |url=https://www.climatewatchdata.org/ghg-emissions?breakBy=gas&end_year=2019&gases=n2o&start_year=1990 |access-date=2023-05-04 |website=www.climatewatchdata.org}}</ref>

Most of the {{chem|N|2|O}} emitted into the atmosphere, from natural and anthropogenic sources, is produced by [[microorganism]]s such as [[denitrifying bacteria]] and [[fungus|fungi]] in soils and oceans.<ref name="Sloss1992">{{cite book|last=Sloss |first=Leslie L. |title=Nitrogen Oxides Control Technology Fact Book |url=https://books.google.com/books?id=--C_JAU7W8QC&pg=PA6 |year=1992 |publisher=William Andrew |isbn=978-0-8155-1294-3 |page=6}}</ref> Soils under natural vegetation are an important source of nitrous oxide, accounting for 60% of all naturally produced emissions. Other natural sources include the oceans (35%) and atmospheric chemical reactions (5%).<ref name="inputs">U.S. Environmental Protection Agency (2010), "[https://nepis.epa.gov/Exe/ZyPDF.cgi/P100717T.PDF?Dockey=P100717T.PDF Methane and Nitrous Oxide Emissions from Natural Sources]". Report EPA 430-R-10-001.</ref> [[Wetland]]s can also be [[Greenhouse gas emissions from wetlands|emitters of nitrous oxide]].<ref name=":4">{{Cite journal |last=Bange |first=Hermann W. |date=2006 |title=Nitrous oxide and methane in European coastal waters |url=https://linkinghub.elsevier.com/retrieve/pii/S0272771406002496 |journal=Estuarine, Coastal and Shelf Science |language=en |volume=70 |issue=3 |pages=361–374 |bibcode=2006ECSS...70..361B |doi=10.1016/j.ecss.2006.05.042|url-access=subscription }}</ref><ref name=":3">{{cite journal |last1=Thompson |first1=A. J. |last2=Giannopoulos |first2=G. |last3=Pretty |first3=J. |last4=Baggs |first4=E. M. |last5=Richardson |first5=D. J. |date=2012 |title=Biological sources and sinks of nitrous oxide and strategies to mitigate emissions |journal=Philosophical Transactions of the Royal Society B |volume=367 |issue=1593 |pages=1157–1168 |doi=10.1098/rstb.2011.0415 |pmc=3306631 |pmid=22451101}}</ref> Emissions from thawing [[permafrost]] may be significant, but as of 2022 this is not certain.<ref name="ar6" />

The main components of anthropogenic emissions are fertilised agricultural soils and livestock manure (42%), runoff and leaching of fertilisers (25%), biomass burning (10%), fossil fuel combustion and industrial processes (10%), biological degradation of other nitrogen-containing atmospheric emissions (9%) and human [[sewage]] (5%).<ref name="denman">K. L. Denman, G. Brasseur, et al. (2007), "Couplings Between Changes in the Climate System and Biogeochemistry".  In ''Fourth Assessment Report of the Intergovernmental Panel on Climate Change'', Cambridge University Press.</ref><ref>{{Cite book |url=http://www.fao.org/docrep/010/a0701e/a0701e00.HTM |title=Livestock's long shadow: Environmental issues and options |publisher=Fao.org |author1=Steinfeld, H. |author2=Gerber, P. |author3=Wassenaar, T. |author4=Castel, V. |author5=Rosales, M. |author6=de Haan, C. |access-date=2 February 2008 |year=2006}}</ref><ref name="epaUpdated">{{cite web|url=https://www3.epa.gov/climatechange/ghgemissions/gases/n2o.html |title=Overview of Greenhouse Gases: Nitrous Oxide |publisher=U.S. Environmental Protection Agency |access-date=31 March 2016|date=23 December 2015 |url-status=live |archive-url= https://web.archive.org/web/20160812082641/https://www.epa.gov/ghgemissions/overview-greenhouse-gases |archive-date=12 August 2016 }}</ref><ref name="epa">{{cite web |url= http://www.epa.gov/nitrousoxide/sources.html |title=Nitrous Oxide: Sources and Emissions |publisher=U.S. Environmental Protection Agency |access-date=2 February 2008 |year=2006  |archive-url= https://web.archive.org/web/20080116204312/http://www.epa.gov/nitrousoxide/sources.html |archive-date=16 January 2008}}</ref><ref>IPCC. 2013. Climate change: the physical basis (WG I, full report). p. 512.</ref> Agriculture enhances nitrous oxide production through soil cultivation, the use of nitrogen [[Fertilizer|fertilisers]] and animal waste handling.<ref>{{Cite journal|last1=Thompson|first1=R. L.|last2=Lassaletta|first2=L.|last3=Patra|first3=P. K.|last4=Wilson|first4=C. |last5=Wells|first5=K. C.|last6=Gressent|first6=A.|last7=Koffi|first7=E. N.|last8=Chipperfield|first8=M. P.|last9=Winiwarter|first9=W. |last10=Davidson|first10=E. A.|last11=Tian|first11=H.|display-authors=3|date=2019-11-18|title=Acceleration of global N 2 O emissions seen from two decades of atmospheric inversion|journal=Nature Climate Change|language=en|volume=9|issue=12 |pages=993–998|doi=10.1038/s41558-019-0613-7|issn=1758-6798|bibcode=2019NatCC...9..993T|s2cid=208302708|hdl=11250/2646484|url=http://pure.iiasa.ac.at/id/eprint/16173/1/N2O_trends_revision2_v1_clean.pdf |hdl-access=free}}</ref> These activities stimulate naturally occurring bacteria to produce more nitrous oxide. Nitrous oxide emissions from soil can be challenging to measure as they vary markedly over time and space,<ref>{{cite journal |last1=Molodovskaya |first1=Marina |last2=Warland |first2=Jon |last3=Richards |first3=Brian K. |last4=Öberg |first4=Gunilla |last5=Steenhuis |first5=Tammo S. |title=Nitrous Oxide from Heterogeneous Agricultural Landscapes: Source Contribution Analysis by Eddy Covariance and Chambers |journal=Soil Science Society of America Journal |date=2011 |volume=75 |issue=5 |page=1829 |doi=10.2136/SSSAJ2010.0415|bibcode=2011SSASJ..75.1829M }}</ref> and the majority of a year's emissions may occur when conditions are favorable during "hot moments"<ref>{{cite journal | last1 = Molodovskaya | first1 = M. | last2 = Singurindy | first2 = O. | last3 = Richards | first3 = B. K. | last4 = Warland | first4 = J. S. | last5 = Johnson | first5 = M. | last6 = Öberg | first6 = G. | last7 = Steenhuis | first7 = T. S. | year = 2012 | title = Temporal variability of nitrous oxide from fertilized croplands: hot moment analysis | journal = Soil Science Society of America Journal | volume = 76 | issue = 5| pages = 1728–1740 | doi = 10.2136/sssaj2012.0039 | bibcode = 2012SSASJ..76.1728M | s2cid = 54795634 }}</ref><ref>{{cite journal |last1=Singurindy |first1=Olga |last2=Molodovskaya |first2=Marina |last3=Richards |first3=Brian K. |last4=Steenhuis |first4=Tammo S. |title=Nitrous oxide emission at low temperatures from manure-amended soils under corn (Zea mays L.) |journal=Agriculture, Ecosystems & Environment |date=July 2009 |volume=132 |issue=1–2 |pages=74–81 |doi=10.1016/j.agee.2009.03.001|bibcode=2009AgEE..132...74S }}</ref> and/or at favorable locations known as "hotspots".<ref>{{cite journal | last1 = Mason | first1 = C.W. | last2 = Stoof | first2 = C.R. | last3 = Richards | first3 = B.K. | last4 = Das | first4 = S. | last5 = Goodale | first5 = C.L. | last6 = Steenhuis | first6 = T.S. | year = 2017 | title = Hotspots of nitrous oxide emission in fertilized and unfertilized perennial grasses on wetness-prone marginal land in New York State | journal = Soil Science Society of America Journal | volume = 81 | issue = 3| pages = 450–458 | doi = 10.2136/sssaj2016.08.0249 | bibcode = 2017SSASJ..81..450M }}</ref>

Among industrial emissions, the production of nitric acid and [[adipic acid]] are the largest sources of nitrous oxide emissions. The adipic acid emissions specifically arise from the degradation of the [[nitrolic acid]] intermediate derived from the nitration of [[cyclohexanone]].<ref name="denman"/><ref>{{cite journal|title=Abatement of N{{ssub|2}}O emissions produced in the adipic acid industry|author1=Reimer R. A. |author2=Slaten C. S. |author3=Seapan M. |author4=Lower M. W. |author5=Tomlinson P. E. | journal = Environmental Progress| year = 1994| volume = 13| issue = 2| pages = 134–137| doi = 10.1002/ep.670130217|bibcode=1994EnvPr..13..134R }}</ref><ref>{{cite journal|title=Abatement of N{{ssub|2}}O emissions produced in the adipic acid industry|author1=Shimizu, A. |author2=Tanaka, K. |author3=Fujimori, M. | journal = Chemosphere – Global Change Science| year = 2000| volume = 2| issue = 3–4| pages = 425–434| doi = 10.1016/S1465-9972(00)00024-6|bibcode=2000ChGCS...2..425S}}</ref>

===Biological processes===
Microbial processes that generate nitrous oxide may be classified as [[nitrification]] and [[denitrification]]. Specifically, they include:

* aerobic autotrophic nitrification, the stepwise oxidation of [[ammonia]] ({{chem|NH|3}}) to [[nitrite]] ({{chem|NO|2|−}}) and to [[nitrate]] ({{chem|NO|3|−}})<!-- (Kowalchuk and Stephen, 2001)-->
* anaerobic heterotrophic denitrification, the stepwise reduction of {{chem|NO|3|−}} to {{chem|NO|2|-}}, [[nitric oxide]] (NO), {{chem|N|2|O}} and ultimately {{chem|N|2}}, where facultative anaerobe bacteria use {{chem|NO|3|−}} as an electron acceptor in the respiration of organic material in the condition of insufficient oxygen ({{chem|O|2}})<!-- (Knowles, 1982)-->
* nitrifier denitrification, which is carried out by autotrophic {{chem|NH|3}}-oxidising bacteria and the pathway whereby ammonia ({{chem|NH|3}}) is oxidised to nitrite ({{chem|NO|2|−}}), followed by the reduction of {{chem|NO|2|-}} to nitric oxide (NO), {{chem|N|2|O}} and molecular nitrogen ({{chem|N|2}})<!-- (Webster and Hopkins, 1996; Wrage et al., 2001)-->
* heterotrophic nitrification<!-- (Robertson and Kuenen, 1990)-->
* aerobic denitrification by the same heterotrophic nitrifiers<!-- (Robertson and Kuenen, 1990) -->
* fungal denitrification<!-- (Laughlin and Stevens, 2002) -->
* non-biological chemodenitrification<!-- (Chalk and Smith, 1983; Van Cleemput and Baert, 1984; Martikainen and De Boer, 1993; Daum and Schenk, 1998; Mørkved et al., 2007)-->

These processes are affected by soil chemical and physical properties such as the availability of mineral nitrogen and [[organic matter]], acidity and soil type, as well as climate-related factors such as soil temperature and water content. <!--(Mosier, 1994; Bouwman, 1996; Beauchamp, 1997; Yamulki et al. 1997; Dobbie and Smith, 2003; Smith et al. 2003; Dalal et al. 2003) -->

The emission of the gas to the atmosphere is limited greatly by its consumption inside the cells, by a process catalysed by the enzyme [[nitrous-oxide reductase|nitrous oxide reductase]].<ref>{{cite book|author1=Schneider, Lisa K. |author2=Wüst, Anja |author3=Pomowski, Anja |author4=Zhang, Lin |author5=Einsle, Oliver |chapter=No Laughing Matter: The Unmaking of the Greenhouse Gas Dinitrogen Monoxide by Nitrous Oxide Reductase |year=2014|title=The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment|pages =177–210| volume =14 |series=Metal Ions in Life Sciences |editor=Kroneck, Peter M. H. |editor2=Sosa Torres, Martha E. |publisher= Springer|doi=10.1007/978-94-017-9269-1_8|pmid=25416395|isbn=978-94-017-9268-4}}</ref>