Tropospheric concentrations of methylchloroform, CH(3)CCl(3), in January 1978 and estimates of the atmospheric residence times for hydrohalocarbons.

The ground level tropospheric concentrations of CH(3)CCl(3) were measured from 55 degrees N to 53 degrees S during the time period around Jan. 1, 1978. The northern temperate zone concentration of CH(3)CCl(3) averaged 94.6 +/- 4.0 x 10(-12) by volume. The southern temperate zone concentration averaged 65.2 +/- 1.3 x 10(-12), for a worldwide average of 80 x 10(-12) by volume. The ratio of concentrations between the two zones is 1.45 +/- 0.07. The observed CH(3)CCl(3) concentrations correspond to 0.52 +/- 0.05 times the atmospheric release to that date, corresponding to an atmospheric residence time of 6.9 +/- 1.2 yr. The atmospheric residence times for 22 other hydrohalocarbon molecules were estimated in comparison to that of CH(3)CCl(3) through the relative rates of reaction with OH radicals.