Ammonia (NH3), NH3
In its pure state and under usual environmental conditions, ammonia exists as a colourless, pungent-smelling gas. It is alkaline, caustic and an irritant. Under high pressure, ammonia can be stored as a liquid. It is highly soluble in water. It reacts with acids to form ammonium salts.
Ammonia is commonly used for bleaching and cleaning, both industrially and in the home. It is used in many and varied industrial processes including the production of fertilisers, plastics, pharmaceuticals, explosives, rubber and petrochemicals. Ammonia also has anti-fungal properties and is used in the control of fungal growth on fruit.
Ammonia is an important substance in the natural nitrogen cycle. The substance is formed from decaying organic matter, especially proteins. In aerobic soils and water, it is converted to nitric acid, which, along with dissolved ammonia itself, is the main form in which land plants take up the nitrogen they need for their growth. Land animals (including humans) excrete excess nitrogen in the form of urea - a compound of ammonia and carbon dioxide. Urea readily breaks down through microbial reaction, releasing ammonia. Ammonia is one of the gases important in 'acid rain', playing an important role in the long-range transport of the acidic pollutants.
The majority of ammonia released to the atmosphere comes from the degradation of animal and human wastes. High levels of nitrogenous fertiliser use (as urea, ammonium nitrate etc.) can result in the leaching of large quantities of nitrate into ground water, which may then be rendered unfit for human consumption, or require expensive treatment to reduce nitrate concentrations to acceptable levels before consumption. Smaller man-made sources of release of ammonia include the use of fertilisers and the decomposition of vegetation and waste, as well as some industrial processes. Minor releases of ammonia include cigarette smoke and infants nappies; humans also emit ammonia in very low levels through sweating and breathing.
Toxic concentrations of ammonia can be liberated from decomposing manure that is confined to a slurry pit or a chicken house. Animals confined near by may then inhale the gas. Vegetation may also be harmed by high local concentrations of ammonia from animal excreta. Other local air impacts are likely to be restricted to odour issues as ammonia can be smelled in the air at quite low concentrations. The biological transformation of ammonium ions (formed when ammonia dissolves in water) to nitrate ions in soils (nitrification) and plant uptake both release acidity into the soil, contributing to soil acidification. High levels of ammonia in babies' nappies can give rise to skin irritation ('nappy rash').