U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


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Published in Micrometeorology in Agricultural Systems (2005) Agronomy Monograph no. 47: 345-379.


Ammonia (NH3) is a colorless gas under standard conditions, whose pungent odor is easily discernible at concentrations above about 10 ppm, and to some persons, down to almost 1 ppm. It is the major basic neutralizing gas in the atmosphere so it has an important role in the neutralization of atmospheric acids generated by the oxidation of sulfur dioxide (SO2) and nitrogen oxides (NOx). As a result, the reaction product of NH3, ammonium (NH4 +), forms an aerosol that is a major component of atmospheric aerosols and in precipitation (Asman et al., 1998). Other organic forms also exist, such as amines and organic N compounds (not currently studied), but the concentrations of these components are generally negligible by comparison (Van der Eerden, 1982).