NOx

In atmospheric chemistry, NO_x is shorthand for nitric oxide (NO) and nitrogen dioxide (NO₂), the nitrogen oxides that are most relevant for air pollution.^[1]^[2] These gases contribute to the formation of smog and acid rain, as well as affecting tropospheric ozone.

NO_x gases are usually produced from the reaction between nitrogen and oxygen during combustion of fuels, such as hydrocarbons, in air; especially at high temperatures, such as in car engines.^[1]^[2]^[3] In areas of high motor vehicle traffic, such as in large cities, the nitrogen oxides emitted can be a significant source of air pollution. NO_x gases are also produced naturally by lightning.

NO_x does not include nitrous oxide (N₂O),^[1] a fairly inert oxide of nitrogen that contributes less severely to air pollution, notwithstanding its involvement in ozone depletion^[4] and high global warming potential.

NO_y is defined as the sum of NO_x plus the NO_z compounds produced from the oxidation of NO_x which include nitric acid, nitrous acid (HONO), dinitrogen pentoxide (N₂O₅), peroxyacetyl nitrate (PAN), alkyl nitrates (RONO₂), peroxyalkyl nitrates (ROONO₂), the nitrate radical (NO₃), and peroxynitric acid (HNO₄).^[5]^[6]^: 30

^ ^a ^b ^c Mollenhauer, Klaus; Tschöke, Helmut (2010). Handbook of Diesel Engines. Springer. pp. 445–6. ISBN 978-3-540-89082-9.
^ ^a ^b Omidvarborna; et al. (December 2015). "NOx emissions from low-temperature combustion of biodiesel made of various feedstocks and blends". Fuel Processing Technology. 140: 113–8. doi:10.1016/j.fuproc.2015.08.031.
^ Annamalai, Kalyan; Puri, Ishwar K. (2007). Combustion Science and Engineering. CRC Press. p. 775. ISBN 978-0-8493-2071-2.
^ Ravishankara, A. R.; Daniel, J. S.; Portmann, R. W. (2009). "Nitrous Oxide (N₂O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century". Science. 326 (5949): 123–5. Bibcode:2009Sci...326..123R. doi:10.1126/science.1176985. PMID 19713491. S2CID 2100618.
^ US Environmental Protection Agency. "Air Monitoring Instrumentation Nitrogen Oxides (NOy)" (PDF).
^ Seinfeld, John H.; Pandis, Spyros N. (2016-03-29). Atmospheric chemistry and physics : from air pollution to climate change (3rd ed.). Wiley. ISBN 978-1-119-22116-6. OCLC 929985467.

[Mollenhauer2010-1] Mollenhauer, Klaus; Tschöke, Helmut (2010). Handbook of Diesel Engines. Springer. pp. 445–6. ISBN 978-3-540-89082-9.

[sciencedirect.com-2] Omidvarborna; et al. (December 2015). "NOx emissions from low-temperature combustion of biodiesel made of various feedstocks and blends". Fuel Processing Technology. 140: 113–8. doi:10.1016/j.fuproc.2015.08.031.

[Annamalai2007-3] Annamalai, Kalyan; Puri, Ishwar K. (2007). Combustion Science and Engineering. CRC Press. p. 775. ISBN 978-0-8493-2071-2.

[sciozo-4] Ravishankara, A. R.; Daniel, J. S.; Portmann, R. W. (2009). "Nitrous Oxide (N₂O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century". Science. 326 (5949): 123–5. Bibcode:2009Sci...326..123R. doi:10.1126/science.1176985. PMID 19713491. S2CID 2100618.

[5] US Environmental Protection Agency. "Air Monitoring Instrumentation Nitrogen Oxides (NOy)" (PDF).

[SeinfeldPandis-3rd-6] Seinfeld, John H.; Pandis, Spyros N. (2016-03-29). Atmospheric chemistry and physics : from air pollution to climate change (3rd ed.). Wiley. ISBN 978-1-119-22116-6. OCLC 929985467.

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