Decline of hexachlorocyclohexane in the Arctic atmosphere and reversal of air‐sea gas exchange

Abstract

Hexachlorocyclohexanes (HCHs) are the most abundant organochlorine pesticides in the arctic atmosphere and ocean surface water. A compilation of measurements made between 1979–93 from stations in the Canadian and Norwegian Arctic and from cruises in the Bering and Chukchi seas indicates that atmospheric concentrations of α‐HCH have declined significantly (p < 0.01), with a time for 50% decrease of about 4 y in summer‐fall and 6 y in winter‐spring. The 1992–93 levels of about 100 pg m −3 are 2–4 fold lower than values in the mid‐1980s. The trend in γ‐HCH is less pronounced, but a decrease is also suggested from measurements in the Canadian Arctic and the Bering‐Chukchi seas. HCHs in ocean surface water have remained relatively constant since the early 1980s. The decline in atmospheric α‐HCH has reversed the net direction of air‐sea gas exchange to the point where some northern waters are now sources of the pesticide to the atmosphere instead of sinks.