Ammonia, tropospheric radical

The temperature and density structure of the troposphere, along with the concentrations of major constituents, are well documented and altitude profiles have been measured over a wide range of seasons and latitudes for the minor species water, carbon dioxide, and ozone. A few profiles are available for carbon monoxide, nitrous oxide, methane, and molecular hydrogen, while only surface or low-altitude measurements have been made for nitric oxide, nitrogen dioxide, ammonia, sulfur dioxide, hydrogen sulfide, and nonmethane hydrocarbons. No direct measurements of nitric acid and formaldehyde are available, though indirect information does exist. The concentrations of a number of other important species, such as peroxides and oxy and peroxy radicals, have never been determined. Therefore, while considerable information concerning trace constituent concentrations is available, the picture is far from complete. 

The reported measured rate constant for reaction of hydrazine with atmospheric hydroxyl (OH) radicals producing ammonia and nitrogen gas was 6.lx 10 cm molecule s (Harris et al. 1979). The rate constant for 1,1-dimethylhydrazine was not measured since the chemical decomposed rapidly in the test system, but the value was estimated at 5 /10 cm molecule s . Assuming an average OH radical concentration of about 10 molecLile/cm . the tropospheric half-lives ofboth chemicals due to reaction with OH were estimated to be about 3 hours. The half-lives are expected to range from less than 1 hour in polluted urban air to 3-6 hours in less polluted atmospheres (Tuazon et al. 1981). 

It was also proposed in the literature (e.g. Crutzen, 1974) that a non-negligible part of NHj is converted in the troposphere into nitrogen oxides. The first step of this conversion is the reaction between ammonia and OH free radicals ... 

Tables 9-8 summarizes the budget of N20 in the troposphere. In addition to emanations from soils and seawater, N20 is released from polluted rivers and estuaries, as a product in the burning of agricultural wastes and biomass, and in the combustion of fossil fuels. Yet another source process of uncertain magnitude is the reaction NH2+N02— N20 + H20 associated with the oxidation of ammonia by OH radicals.

The lifetime of NH3 under solar radiation is very short (2[Pg.233]

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