Sources and seasonality of polycyclic aromatic hydrocarbons transported to Alert, Canadian Arctic

A probabilistic function (integrated source contribution function, ISCF) based on backward air mass trajectory calculation was developed to track sources and atmospheric pathways of polycyclic aromatic hydrocarbons (PAHs) to the Canadian High Arctic station of Alert. In addition to the movement of air masses, the emission intensities at the sources and the major processes of partition, indirect photolysis, and deposition occurring on the way to the Arctic were incorporated into the ISCF. The predicted temporal trend of PAHs at Alert was validated by measured PAH concentrations throughout 2004. The PAH levels in the summer are orders of magnitude lower than those in the winter and spring when long-range atmospheric transport events occur more frequently. PAHs observed at Alert are mostly from East Asia (including Russia Far East), North Europe (including European Russia), and North America. These sources account for 25, 45, and 27% of PAHs atmospheric level at Alert, respectively. Source regions and transport pathways contributing to the PAHs contamination in the Canadian High Arctic vary seasonally. In the winter, Russia and Europe are the major sources. PAHs from these sources travel eastward and turn to the north at approximately 120°E before reaching Alert, in conjunction with the well- known Arctic haze events. In the spring, PAHs from Russia and Europe first migrate to the west and then turn to the north at 60°W toward Alert. The majority of PAHs in the summer are from northern Canada where they are carried to Alert via low- level transport pathways. In the fall, 70% of PAHs arriving at Alert are delivered from North American sources.

本研究开发了一种基于气团后向轨迹计算的概率函数——积分源贡献函数（Integrated Source Contribution Function, ISCF），用于追踪加拿大高纬度北极警戒站（Alert）接收的多环芳烃（Polycyclic Aromatic Hydrocarbons, PAHs）的来源与大气传输路径。除气团运动外，源排放强度以及在向北极输送途中发生的分配、间接光解和沉降等主要过程，均被纳入该ISCF模型。通过2004年全年实测的PAHs浓度数据，对警戒站PAHs的预测时间变化趋势进行了验证。夏季PAH浓度较冬季和春季低数个数量级，而冬春季节大气长距离传输事件发生更为频繁。警戒站观测到的PAHs主要来自东亚（含俄罗斯远东地区）、北欧（含俄罗斯欧洲部分）以及北美，上述源区分别贡献了警戒站大气中25%、45%和27%的PAHs。影响加拿大高纬度北极地区PAHs污染的源区与传输路径存在显著季节差异。冬季，俄罗斯与欧洲为主要源区。来自这些源区的PAHs向东输送，并在约东经120°处转向北，最终抵达警戒站，该输送过程与广为人知的北极霾事件相伴发生。春季，来自俄罗斯与欧洲的PAHs先向西迁移，随后在西经60°处转向北，向警戒站输送。夏季绝大多数PAHs来自加拿大北部，通过近地面传输路径被输送至警戒站。秋季，抵达警戒站的PAHs中有70%来自北美源区。