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today. The recognition that the Earth's atmosphere is being affected by human activity and that a large fraction of the chemistry in the atmosphere is due to free radicals stimulated laboratory studies on �tmospheric free radical reactions in the 1970s and 1980s. Free radical reactions in the oxidation of methane constitute one of the areas that has received a great deal of attention and, consequently, it is better understood than most. I have attempted to review the reactions taking place in the atmospheric oxidation of methane. Methane is the simplest hydrocarbon and the most abundant hydro carbon in the Earth's atmosphere. Its concentration is at least a thousand times greater than the next most abundant hydrocarbon. Atmospheric methane concentration has been increasing since the onset of the industrial era (l a,b) and the growth has accelerated in the last two decades (2a,b). The reasons for the increase are not clear. The CH4 flux into the atmosphere may be increasing or its loss rate from the atmosphere may be decreasing. The oxidation of methane generates nearly 30% of the atmospheric CO 1 The US Government has the right to retain a nonexclusive, royalt y-free license in and to any copyright covering this paper.
A R Ravishankara (Sat,) studied this question.