(Table 1) Annual mean concentrations of atmospheric a- and g-Hexachlorocyclohexane at stations Alert, Canada and Zeppelin, Norway@en

Twelve year datasets of weekly atmospheric concentrations of alpha- and gamma-HCH were compared between the two Arctic monitoring stations of Alert, Nunavut, Canada, and Zeppelin Mountain, Svalbard, Norway. Time-series analysis was conducted with the use of dynamic harmonic regression (DHR), which provided a very good model fit, to examine both the seasonal behaviour in these isomers and the longer-term, underlying trends. Strong spatial differences were not apparent between the two sites, although subtle differences in seasonal behaviour and composition were identified. For example, the composition of gamma-HCH to total HCH (alpha + gamma) was greater at Zeppelin compared to Alert, probably reflecting this site's proximity to major use regions of lindane. Pronounced seasonality in air concentrations for gamma-HCH was marked by a 'spring maximum event' (SME), confirming earlier studies. For alpha-HCH, the SME was much weaker and only evident at Alert, whereas at Zeppelin, seasonal fluctuations for alpha-HCH were marked by elevated concentrations in summer and lower concentrations during winter, with this pattern most apparent for the years after 2000. We attribute this difference in spatial and temporal patterns to the Arctic oscillation. A similar climatic pattern was not evident at either site in the gamma-HCH data. Seasonally adjusted, long-term trends revealed declining concentrations at both sites for alpha- and gamma-HCH over the entire time-series. Recent legislation affecting lindane use appear to account for this decline in gamma-HCH, with little evidence of a delay or 'lag' between the banning of lindane in Europe (a main source region) or Canada, and a decline in air concentrations observed at both Arctic sites.针对加拿大努纳武特地区阿勒特（Alert）与挪威斯瓦尔巴群岛齐柏林山（Zeppelin Mountain）两处北极监测站点，本研究对其为期12年的每周大气中α-六氯环己烷（alpha-HCH）与γ-六氯环己烷（gamma-HCH）浓度数据集展开对比分析。本研究采用动态谐波回归（dynamic harmonic regression, DHR）方法开展时间序列分析，该模型拟合效果优异，用于探究这两种六氯环己烷异构体的季节分布特征与长期潜在趋势。尽管两处站点的季节分布特征与组分占比存在细微差异，但未观测到显著的空间差异。例如，齐柏林山站点的γ-HCH占总六氯环己烷（alpha-HCH+gamma-HCH）的比例高于阿勒特站点，这大概率反映出该站点邻近林丹（lindane）的主要使用区域。γ-HCH的大气浓度呈现显著季节特征，以‘春季峰值事件（spring maximum event, SME）’为典型表现，这一结果验证了此前的相关研究结论。而对于α-HCH，春季峰值事件则相对微弱，且仅在阿勒特站点可观测到；齐柏林山站点的α-HCH季节波动则表现为夏季浓度升高、冬季浓度降低，这一模式在2000年后的观测年份中尤为显著。我们将这种空间与时间分布模式的差异归因于北极涛动（Arctic oscillation）。γ-HCH的浓度数据中未在两处站点观测到类似的气候关联模式。经季节校正后的长期趋势分析显示，在整个观测时间序列内，两处站点的α-HCH与γ-HCH浓度均呈下降趋势。近期针对林丹使用的相关立法或可解释γ-HCH浓度的下降现象；在欧洲（主要使用区域）与加拿大禁用林丹后，两处北极监测站点的大气浓度均出现下降，且未观测到明显的延迟或滞后效应。