Hexachlorocyclohexanes in air in southern Norway. Temporal variation, source allocation, and temperature dependence

Concentrations of alpha- and gamma-hexachlorocyclohexane (HCH) were measured 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 concentrations in air was characterized by a generally low base line level with a few spring-time episodes of highly elevated concentrations. Under this pattern of episodic concentration spikes lies a background with 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 up to 1000 pg/m(3) coincided with air transport from Western Central Europe, 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 usage pattern of HCH pesticides in different regions of Europe and points toward regional atmospheric transport as the major source of these chemicals, especially gamma-HCH. Short episodes of elevated concentrations proved to be very important when trying to quantify the atmospheric input of gamma-HCH into southern Norway, whereas alpha-HCH levels are more strongly influenced by the global background situation. Air concentrations and alpha/gamma concentration ratios were clearly correlated with air mass origin.