Code: AN
Site types that use this protocol: Terrestrial

Natural and man-made sources emit oxides of nitrogen in approximately equal quantities, but, whilst the former tend to have equal world-wide distribution and are relatively constant over time, the latter are concentrated in or around centres of population.  Nitric oxide (NO) and nitrogen dioxide (NO2) are the most important oxides of nitrogen in urban atmospheres and it is NO2 which has the more significant health and ecosystem effects.  Major sources of NO2 in urban areas result from fuel combustion in motor vehicles, power generation, heating plants and industrial processes, mostly by oxidation of NO emissions from these sources.  NO2 is a respiratory tract irritant, is toxic at high concentrations and is involved in the formation of photochemical smog and acid rain.  It can also cause direct damage to crops and other vegetation, together with SO2 and ozone (UNEP/WHO 1994).  High concentrations of NO2 can have an indirect effect on ecosystems by providing an increased nitrogen input and this is important in the context of systems with a low natural nitrogen demand.

Passive diffusion tubes are used to measure the concentration of Nitrogen Dioxide (NO2).  The tubes are left out for a two-week period.

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