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Nitrogen oxides, NO and NO2 as NO2

oxides of nitrogen

SPRI Emission Reporting Threshold
100,000 Kg/yr Pollutant Emissions to Air
This sheet is a generic summary, designed to give the reader a basic level of background information about the substance in question. Great care has been taken to represent as effectively and correctly as possible the broad range of (not necessarily consistent) information which is available from a variety of sources. The reader must accept therefore that this sheet has no legal status and cannot be relied upon in any legal proceedings. SEPA disclaims any responsibility or liability whatsoever for errors and omissions in this sheet.
What is it?
Oxides of nitrogen (NOx) is the term usually used to refer to nitrogen monoxide (nitric oxide or NO; a colourless and odourless gas) and nitrogen dioxide (NO2; a red-brown gas with a pungent smell which is soluble in water). Nitrogen monoxide reacts with oxygen or ozone in the air to produce nitrogen dioxide. Oxides of nitrogen occur both naturally as well as being produced by man's activities.
What is it used for?
Nitrogen monoxide is used in the manufacture of a variety of important chemicals. Nitrogen dioxide is a powerful oxidising agent used in chemical processes and rocket fuels. It is also used to produce nitric acid which is widely used.
Where does it come from?
The main man-made releases of nitrogen oxides are from the burning of fossil fuels (including vehicle emissions), biomass burning (burning of forest and agricultural lands following harvest) and some production processes. Small amounts are released naturally in lightning, natural fires and from microbial processes in soils and water bodies.
How might it affect the environment?
Species containing nitrogen are essential for plant nutrition. However, high levels of nitrogen dioxide and nitrogen monoxide damage plant life. Nitrogen dioxide also contributes to the formation of acid rain which damages vegetation, buildings and water bodies. Nitrogen dioxide is also involved in the formation of ground level ozone which damages vegetation and other materials. Nitrogen dioxide can react with other air pollutants to form peroxyacetyl nitrates (PANs) which then carry reactive and potentially damaging nitrogen-containing species for long distances.
How might exposure to it affect human health?
Inhalation of higher than average environmental levels of nitrogen dioxide / nitrogen monoxide (found around congested urban roads for example) can cause respiratory problems, particularly in sensitive individuals such as asthmatics. Similar problems are experienced by sensitive individuals such as asthmatics after inhalation of ozone (which is formed using nitrogen dioxide). Nitrogen monoxide is also found naturally in the body and is involved in the cardiovascular (heart and blood circulation) and immune (disease protection) systems.
What steps are being taken to limit the potential impacts?
The main legislation controlling levels of nitrogen dioxide in the UK (including Scotland) is the National Air Quality Strategy, in which it is one of the eight main air pollutants targeted for reduction; and, from large industrial processes, through the UK's Pollution Prevention and Control (PPC) regulations. The European Directive on Integrated Pollution Prevention and Control (IPPC) and that concerned with ambient air quality assessment and management (96/62/EC) also control industrial and general nitrogen dioxide releases respectively. The UK is also a signatory to the international UNECE Convention on Long-Range Transboundary Air Pollutants (LRTAP) which includes measures to combat the effects of oxides of nitrogen.