Methane in the atmosphere.

Abstract

Methane is present in the troposphere with a volume concentration of about 1.5 ppm. Estimates of Koyama indicate a predominantly biological origin with a total production rate of about 2.7 x 10/sup 14/ g CH/sub 4//yr. From that the author estimated the atmospheric lifetime of methane to be around 20 years. Measurements of the C-14 in methane by Libby and later by Bainbridge, et al. gave a C-14 content of 75% of recent wood and, therefore, confirm the predominant biological origin, the addition of inactive CH; from industrial sources being only about 25%. Much less is known about sinks of CH/sub 4/. Cadle reported fairly high destruction rates by atomic O, a reaction which should be important at high altitude. Bainbridge reports a decrease in the measured methane concentration above the tropopause. He, however, considers this decrease too small to account for the destruction rate of 20 years estimated by Koyama. Measurements on air samples collected on aircraft flights at various altitudes show a high variability of the CH/sub 4/ content both with time and altitude.