Global baseline pollution studies: X. Atmospheric halocarbons: Global budget estimations for tetrachloroethene, 1,2-dichloroethane, 1,1,1,2-tetrachloroethane, hexachloroethane and hexachlorobutadiene. Estimation of the hydroxyl radical concentrations in the troposphere of the northern and southern hemisphere
On the basis of air samples from sampling sites far away from anthropogenic sources in the region of the North and South Atlantic and the Indian Ocean it is possible to determine the tropospheric burden of tetrachloroethene, 1,2-dichloroethane, 1,1,1,2-tetrachloroethane, hexachloroethane and hexachlorobutadiene. Using the global distribution figures and the emission rates for tetrachloroethane and a two-box model for the troposphere, we estimate the hydroxyl radical concentration to about (7±3) and (17±7) × 105 molecules × cm−3 for the northern (NH) and southern (SH) hemisphere, respectively. For three chloroethanes and for hexachlorobutadiene the atmospheric lifetime in both hemispheres and the global emission rates can be estimated. The following results are obtained: tetrachloroethene: emissions 530 ktons per year, lifetime 0.46±0.1 year (NH), 0.18±0.05 year (SH); 1,2-dichloroethane: emissions 400–500 ktons per year, lifetime 0.32±0.1 year (NH), 0.13±0.04 year (SH); 1,1,1,2-tetrachloroethane: emissions about 3.6 ktons per year, lifetime 0.7 year (NH), 0.3 year (SH); hexachloroethane: emissions less than 1 kton per year, very long tropospheric lifetime; hexachlorobutadiene: emissions about 3 ktons per year, lifetime 2.3 year (NH) and 0.8 year (SH).
