HEXACHLOROCYCLOHEXANES IN AIR IN SOUTHERN NORWAY - TEMPORAL VARIATION, SOURCE ALLOCATION, AND TEMPERATURE-DEPENDENCE

Concentrations of alpha- and gamma-hexachlorocyclohexane (HCH) were me asured in ambient air samples on a weekly basis between 1991 and 1995 at Lista, a coastal station in southern Norway. The levels averaged at 66 pg/m(3) alpha-HCH and 48 pg/m(3) gamma-HCH. A 50% decline of alpha -HCH concentrations in air could be observed during the 5 year period, while no such trend was found for gamma-HCH. The time profile of conc entrations in air was characterized by a generally low base line level with a few spring-time episodes of highly elevated concentrations. Un der this pattern of episodic concentration spikes lies a background wi th seasonally variable gamma-HCH levels, showing higher concentrations at higher temperatures. alpha-HCH concentrations in air are far less temperature sensitive. Episodes with air concentrations of gamma-HCH u p to 1000 pg/m(3) coincided with air transport from Western Central Eu rope, whereas episodes with elevated alpha-HCH levels up to 300 pg/m(3 ) tended to correlate with air transport from easterly directions, but did no longer occur in 1994 and 1995. This is in agreement with the u sage pattern of HCH pesticides in different regions of Europe and poin ts toward regional atmospheric transport as the major source of these chemicals, especially gamma-HCH. Short episodes of elevated concentrat ions proved to be very important when trying to quantify the atmospher ic input of gamma-HCH into southern Norway, whereas alpha-HCH levels a re more strongly influenced by the global background situation. Air co ncentrations and alpha/gamma concentration ratios were clearly correla ted with air mass origin.