The oxidation of ammonia, hydrogen sulfide, and methane in nonurban tropospheres


  • T. E. Graedel


Kinetic calculations of the photochemistry of the nonurban troposphere have been performed to assess the oxidation of ammonia, hydrogen sulfide, and methane. In each case this oxidation proceeds by hydroxyl radical abstraction of a hydrogen atom, followed by peroxy radical formation. These abstraction reactions have low rates in the troposphere; thus little participation of NH3, H2S, and CH4 in gas phase tropospheric chemistry occurs. In the case of ammonia, two radical reactions or one radical reaction plus an NO reaction are required to produce nitric oxide. As a result, NO production from NH3is unimportant, most of the ammonia being incorporated into aerosols. Hydrogen sulfide oxidation is nearly as slow as that of ammonia, producing SO2 concentrations of ∼1 ppb and little sulfate. Anthropogenic sources may thus be important in the production of sulfate aerosol even in remote areas. Methane oxidation is perhaps best assessed by comparing its rate with the rates of carbon monoxide and the terpenes. Although the methane rate is about twice that of CO, it is 10 times less than that of the terpenes. The terpenes thus dominate much of the gas phase chemistry of the nonurban troposphere.