THE SEASONAL-VARIATION OF SELECTED NATURAL AND ANTHROPOGENIC HALOCARBONS IN THE ARCTIC TROPOSPHERE

Weekly average concentrations of four natural halocarbons (bromoform, dibromochloromethane, bromochloromethane, chloroiodomethane) and three anthropogenic halocarbons (trichloroethylene, tetrachloroethylene, an d trans-1,2 dichloroethylene) were measured at Alert, Canada, from Jan uary 1992 to June 1994. Air samples were collected on Tenax TA adsorbe nt, and were analyzed with capillary GC/MS (SIM). Most of the measured halocarbons showed significant seasonal variation. The winter/summer ratio of mixing ratios was as much as 60 for trichloroethylene and 3 f or bromoform. The winter/summer differences are closely related to che mical reactivity in the atmosphere, and higher reactive loss in summer during long-range transport from mid-latitudinal sources.