Nitrogen oxides (NOx)

NOx, Kväveoxider (NO+NO2) som kvävedioxid

 Nitrogen oxides (NO_X) is the collective name for nitrogen monoxide (NO) and nitrogen dioxide (NO₂)^{1 2}. NO is a colourless, poisonous and odourless gas whereas NO₂ is a reddish to brown poisonous gas with a sharp, pungent odour³.

Uses

Nitrogen dioxide is used as a potent oxidation agent in various chemical processes within industry. Nitrogen dioxide is also used in industrial production of nitric acid^{4 5 6}.

Sources and transportation pathways

Nitrogen oxides are formed when nitrogen and oxygen react at high temperatures. Emissions of nitrogen oxides are therefore strongly connected to combustion processes⁷. Nitrogen oxides are emitted to air, where it reacts (to nitrate or nitric acid) and is deposited to land⁸. The reaction may occur both before and after deposition⁹. Nitrogen oxides contribute, together with volatile organic compounds (NMVOC) and sunlight, to formation of ground level ozone.

Examples of natural sources of nitrogen oxides are forest fires and lightning¹⁰. In Sweden the transport sector is the single largest source of nitrogen oxides¹¹. Of the large point sources, the pulp and paper industry, energy industries and the metal industry are the main contributors to national emissions¹².

Effects on environment and health

Deposition of nitrogen oxides results in acidification and eutrophication of land and water¹³. Acidification harms plants and animals, both on land and in water¹⁴. When the ground turns acidic, vital nutrients are leached from the soil, which eventually may result in reduced forest growth. Furthermore, metals are released in the ground that can harm decomposing organisms in the ground as well as birds and mammals higher up in the food chain, including humans¹⁵. Eutrophication occurs when there is an excess of nutrients (e.g. nitrogen) in land or water ¹⁶. The abundance of nutrients threatens biological diversity by allowing species that thrive in a nutrient-rich environment to outcompete species that are adapted to a more nutrient-poor environment ¹⁷.

Ground level ozone may damage vegetation and during episodes of high levels, humans may be affected by irritation of the respiratory tract¹⁸. Nitrogen oxides are poisonous and may irritate the respiratory tract and mucosal membranes.¹⁹ Epidemiological studies have shown an increase of symptoms of bronchitis in asthmatic children in connection with long-term exposure to nitrogen dioxide²⁰. 

International agreements and regulations

Nitrogen oxides are regulated by the UN Convention on Long-range Transboundary Air Pollution (CLRTAP) and the UN Framework Convention on Climate Change (UNFCCC) as well as by the EU National Emissions Ceilings Directive (2001/81/EC), the EU Air Quality Directive (2008/50/EC) and the EU Industrial Emissions Directive (2010/75/EU). The UN Protocol on PRTRs and the EU E-PRTR regulation regulate how data on nitrogen oxide emissions is made available.



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¹ http://www.naturvardsverket.se/Sa-mar-miljon/Statistik-A-O/Kvaveoxid-till-luft/
² http://www.norskeutslipp.no/no/Komponenter/Utslipp/Nitrogenoksider/?ComponentType=utslipp&ComponentPageID=159&SectorID=90
³ http://www.ne.se/uppslagsverk/encyklopedi/l%C3%A5ng/kv%C3%A4veoxider
⁴ http://www.npi.gov.au/resource/oxides-nitrogen-0
⁵ http://prtr.ec.europa.eu/#/pollutantinfo
⁶ http://www.norskeutslipp.no/en/Components/Emission/Nitrogen-oxides/?ComponentType=utslipp&ComponentPageID=159&SectorID=90
⁷ http://www.naturvardsverket.se/Sa-mar-miljon/Klimat-och-luft/Luftfororeningar/Kvaveoxider/
⁸ https://www.naturvardsverket.se/Documents/publikationer/91-620-8089-X.pdf?pid=3879
⁹ https://www.naturvardsverket.se/Documents/publikationer/91-620-8089-X.pdf?pid=3879
¹⁰ http://www.npi.gov.au/resource/oxides-nitrogen-0
¹¹ http://www.naturvardsverket.se/Sa-mar-miljon/Statistik-A-O/Kvaveoxid-till-luft/
¹² http://www.naturvardsverket.se/Sa-mar-miljon/Klimat-och-luft/Luftfororeningar/Kvaveoxider/
¹³ http://www.naturvardsverket.se/Sa-mar-miljon/Klimat-och-luft/Luftfororeningar/Kvaveoxider/
¹⁴ https://www.eea.europa.eu/publications/air-quality-in-europe-2016
¹⁵ http://www.airclim.se/f%C3%B6rsurningens-effekter
¹⁶ https://www.eea.europa.eu/publications/air-quality-in-europe-2016
¹⁷ http://www.miljomal.se/sv/Miljomalen/7-Ingen-overgodning/
¹⁸ http://www.miljomal.se/Miljomalen/Alla-indikatorer/Indikatorsida/?iid=104&pl=1
¹⁹ http://www.naturvardsverket.se/Sa-mar-miljon/Klimat-och-luft/Luftfororeningar/Kvaveoxider/
²⁰ http://www.who.int/mediacentre/factsheets/fs313/en/