SEASONAL-VARIATIONS IN THE ATMOSPHERIC DISTRIBUTION OF A REACTIVE CHLORINE COMPOUND, TETRACHLOROETHENE (CCL2=CCL2)

Tropospheric mixing ratios of CCl2=CCl2 were measured at remote surfac e locations in the Pacific between 71 degrees N and 47 degrees S durin g September and December of 1989, and March and June of 1990. The obse rved gradient of decreasing concentrations from the northern to southe rn hemisphere, and very low concentrations in the southern hemisphere throughout the year, indicates a predominant input from the northern h emisphere. Our seasonal measurements in the northern hemisphere showed maximum CCl2=CCl2 concentrations occurring in the late winter and min imum concentrations occurring in the late summer. This distinct season al variation is strongly coupled to the atmospheric abundance of hydro xyl radical, the only important species responsible for CCl2=CCl2 remo val. Using the estimated global CCl2=CCl2 emissions the lifetime is ca lculated 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 hydro xyl reaction rate constant compared with that of methylchloroform (CH3 CCl3).