Total nitrogen, Total N
Nitrogen is a colourless and odourless gas1 with atomic number 7 in the periodic table. The majority, 78 %, of the atmosphere closest to the earth surface, i.e. the troposphere, is made up of nitrogen gas (N2).2 The term total nitrogen describes the total amount of nitrogen and includes ammonium, nitrate and organically bound nitrogen. The nitrogen in nitrate (NO3-) is available to plants (algae) while ammonium (NH4+) is an intermediate form of nitrogen. Organic nitrogen is bound to organic matter and not easily accessible to algae.3
In the food industry, liquid nitrogen is used for quick freezing of food. Nitrogen gas can be used for food packaging to extend the product expiry date. In industry, liquid nitrogen is also used for shrink-fitting, a technology used to join metal parts without the use of bolts or welding. Nitrogen gas is used for nitrogen inerting , which is the process when the air, in for example chemical storage tanks, is replaced with nitrogen gas. This is done in order to prevent flammable chemicals from catching fire. Nitrogen is also used in the production of ammonia, which is the primary feedstock in the production of artificial fertilizer.4, 5
Sources and transportation pathways
Almost half of the total nitrogen influx to the sea originates from natural leakage from forests and land. The remaining amount is anthropogenic.6 Nitrogen reacts with oxygen to form nitrogen oxides at high temperatures. Emissions of nitrogen oxides are therefore strongly related to combustion processes.7 Nitrogen oxide is emitted to air, where it forms nitrate and nitric acid and is deposited on land.8 Nitrogen and hydrogen react to form ammonia, a reaction that occurs both naturally as well as industrially. Ammonia is emitted to air, where it forms ammonium (NH4+), which is deposited to soil, water and vegetation.9 The formation of nitrate from nitrogen oxide, and ammonium from ammonia can occur both before and after deposition.10
The largest point sources of emissions of total nitrogen to water in Sweden are wastewater treatment plants .11 Natural sources of nitrogen oxides include forest fires and lightning storms.12 The largest source of nitrogen oxide emissions to air in Sweden is the transport sector.13 The pulp and paper, energy and metal industries are the largest point sources in Sweden.14 Fertilizer management in agriculture is the single largest source of ammonia emissions in Sweden.15
Effects on environment and health
Deposition of nitrogen results in acidification and eutrophication of soil and water.16 Acidification is harmful for plants and animals, both on land and in water.17 When the soil turns acidic, vital nutrients are leached from the soil, which may eventually result in reduced forest growth. Furthermore, metals in the soil are released that can harm decomposing organisms in the soil as well as birds and mammals higher up the food chain, including humans.18 Eutrophication occurs when there is an excess of nutrients (e.g. nitrogen) in soil or water.19 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.20 Nitrogen oxide contributes, together with volatile organic compounds (NMVOC) and sunlight, to formation of ground level ozone. Ground level ozone may damage vegetation and during episodes of high levels, humans may be affected by irritation of the respiratory tract.
There is a risk of frost bite during handling of liquid nitrogen. As liquid nitrogen is gasified, there is also a risk of oxygen deficiency as the oxygen in the air is displaced.21
International agreements and regulations
Total nitrogen is regulated by the EU directive on Urban Waste Water Treatment (91/271/EEC). Ammonium and nitrate are regulated by the EU Groundwater Directive (2006/118/EC), the EU Water Framework Directive (2000/60/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 total nitrogen emissions is made available. Nitrogen is also included in the EU Marine Strategy Framework Directive (2008/56/EC) that aims to reduce the eutrophication in the Baltic Sea.
1 https://rib.msb.se/Portal/Template/Pages/Kemi/Kemsearch.aspx 2 https://www.smhi.se/kunskapsbanken/meteorologi/luft-1.60343 https://www.havochvatten.se/funktioner/ordbok/ordbok/q---t/ordbok-q-t/2013-03-14-totalkvave-tot-n.html4 http://www.aga.se/sv/products_ren/gas_school/solutions_nitrogen/index.html5Ahlgren, S., Bauer, F., Hulteberg, C. (2015). Produktion av kvävegödsel baserad på förnybar energi - en översikt av teknik, miljöeffekter och ekonomi för några alternativ. Rapport nr 082. Institutionen för energi och teknik, Sveriges lantbruksuniversitet, Uppsala.6http://www.jordbruksverket.se/amnesomraden/miljoklimat/ingenovergodning/jordbruketochovergodningen.4.4b00b7db11efe58e66b80001608.html7 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.eea.europa.eu/publications/air-quality-in-europe-201610 https://www.naturvardsverket.se/Documents/publikationer/91-620-8089-X.pdf?pid=3879 11 http://prtr.ec.europa.eu/ 12 http://www.npi.gov.au/resource/oxides-nitrogen-0 13 http://www.naturvardsverket.se/Sa-mar-miljon/Statistik-A-O/Kvaveoxid-till-luft/14 http://www.naturvardsverket.se/Sa-mar-miljon/Klimat-och-luft/Luftfororeningar/Kvaveoxider/15 http://www.naturvardsverket.se/Sa-mar-miljon/Statistik-A-O/Ammoniak-utslapp-till-luft/16 http://www.naturvardsverket.se/Sa-mar-miljon/Klimat-och-luft/Luftfororeningar/Kvaveoxider/17 https://www.eea.europa.eu/publications/air-quality-in-europe-2016 18 http://www.airclim.se/19 https://www.eea.europa.eu/publications/air-quality-in-europe-2016 20 http://www.miljomal.se/sv/Miljomalen/7-Ingen-overgodning/21 http://www.bmc.uu.se/miljo-och-sakerhet/Arbetsmiljo/regler-hantering-flytande-kvave/