Seasonal variations in the atmospheric distribution of a reactive chlorine compound, tetrachloroethene (CCl₂=CCl₂)

Tropospheric mixing ratios of CCl 2 =CCl 2 were measured at remote surface locations in the Pacific between 71°N and 47°S during September and December of 1989, and March and June of 1990. The observed gradient of decreasing concentrations from the northern to southern hemisphere, and very low concentrations in the southern hemisphere throughout the year, indicates a predominant input from the northern hemisphere. Our seasonal measurements in the northern hemisphere showed maximum CCl 2 =CCl 2 concentrations occurring in the late winter and minimum concentrations occurring in the late summer. This distinct seasonal variation is strongly coupled to the atmospheric abundance of hydroxyl radical, the only important species responsible for CCl 2 =CCl 2 removal. Using the estimated global CCl 2 =CCl 2 emissions the lifetime is calculated to be about 5.4 months which is in good agreement with the 4.0 month estimate obtained from the inverse ratio of its measured hydroxyl reaction rate constant compared with that of methylchloroform (CH 3 CCl 3 ).