The atmospheric cycle of methane

Abstract

The atmospheric distribution of CH 4 is rather uniform zonally and vertically but exhibits a slight gradient with latitude in the troposphere; in the stratosphere it shows a definite decrease with altitude. The average volume mixing ratio in the troposphere is 1.4 ppm which corresponds to a total amount of 4 × 10 15 g of CH 4 present in the atmosphere. Most is of recent biologic origin. C 14 analyses show that no more than 20% is released by fossil sources. The various ecosystems producing CH 4 are discussed and the total annual production is estimated to lie between 5.5 × 10 14 g/yr and 11 × 10 14 g/yr. The corresponding turnover times for atmospheric CH4 range from 4 to 7 yr. The destruction of CH 4 takes place mainly in the troposphere, most probably through the reaction CH 4 + OH ? CH 3 + H 2 O. About 10% of the CH 4 is destroyed in the stratosphere. The CH 4 cycle is strongly coupled to the H 2 and CO cycles and contributes also on the order of 1% to the atmospheric carbon cycle. DOI: 10.1111/j.2153-3490.1974.tb01952.x