Atmospheric HCH Concentrations over the Marine Boundary Layer from Shanghai, China to the Arctic Ocean: Role of Human Activity and Climate Change

From July to September 2008, air samples were collected aboard the research expedition icebreaker XueLong (Snow Dragon) as part of the 2008 Chinese Arctic Research Expedition Program. Hexachlorocyclohexane (HCH) concentrations were analyzed in all of the samples. The average concentrations (+/- standard deviation) over the entire period were 33 +/- 16, 5.4 +/- 3.0, and 13 +/- 7.5 pg m(-3) for alpha-, beta- and gamma-HCH, respectively. Compared to previous studies in the same areas, total HCH (Sigma HCH, the sum of alpha-, beta-, and gamma-HCH) levels declined by more than 10x compared to those observed in the 1990s, but were approximately 4x higher than those measured by the 2003 China Arctic Research Expedition, suggesting the increase of atmospheric Sigma HCH recently. Because of the continuing use of lindane, ratios of alpha/gamma-HCH showed an obvious decrease in North Pacific and Arctic region compared with those for 2003 Chinese Arctic Research Expedition. In Arctic, the level of alpha-HCH was found to be linked to sea ice distribution. Geographically, the average concentration of alpha-HCH in air samples from the Chukchi and Beaufort Seas, neither of which contain sea ice, was 23 +/- 4.4 pg m(-3), while samples from the area covered by seasonal ice (similar to 75 degrees N to similar to 83 degrees N), the so-called floating sea ice region, contained the highest average levels of alpha-HCH at 48 +/- 12 pg m(-3), likely due to emission from sea ice and strong air-sea exchange. The lowest concentrations of alpha-HCH were observed in the pack ice region in the high Arctic covered by multiyear sea ice (similar to 83 degrees N to similar to 86 degrees N). This phenomenon implies that the re-emission of HCH trapped in ice sheets and Arctic Ocean may accelerate during the summer as ice coverage in the Arctic Ocean decreases in response to global climate change.