Polychlorinated biphenyls (PCBs) in the Arctic atmosphere: determining important driving forces using a global atmospheric transport model, 1979-2010

We present a spatially and temporally resolved global atmospheric polychlorinated biphenyl (PCB) model, driven by meteorological data, that is skilled at simulating mean atmospheric PCB concentrations and seasonal cycles in the Northern Hemisphere midlatitudes and mean Arctic concentrations. However, the model does not capture the ob- served Arctic summer maximum in atmospheric PCBs. We use the model to estimate global budgets for seven PCB con- geners, and we demonstrate that congeners that deposit more readily show lower potential for long-range transport, consistent with a recently described "differential removal hypothesis" regarding the hemispheric transport of PCBs. Using sensitivity simulations to assess processes within, outside, or transport to the Arctic, we examine the influence of climate- and emissions-driven processes on Arctic concentrations and their effect on improving the simulated Arctic seasonal cycle. We find evidence that processes occurring outside the Arctic have a greater influence on Arctic atmospheric PCB levels than processes that occur within the Arctic. Our simulations suggest that re-emissions from sea ice melting or from the Arctic Ocean during summer would have to be unrealistically high in order to capture observed temporal trends of PCBs in the Arctic atmosphere. We conclude that midlatitude pro- cesses are likely to have a greater effect on the Arctic under global change scenarios than re-emissions within the Arctic.

本研究构建了一套由气象数据驱动、具备时空分辨能力的全球大气多氯联苯（polychlorinated biphenyl，PCB）模型，该模型可有效模拟北半球中纬度地区的大气PCB平均浓度与季节循环特征，以及北极地区的大气PCB平均浓度水平，但未能复现观测到的北极大气PCB夏季峰值现象。本研究利用该模型估算了7种PCB同系物的全球收支情况，结果表明更易沉积的同系物其长距离传输潜力更低，这与近期提出的关于PCB半球传输的“差异去除假说”相符。通过开展敏感性模拟试验，本研究评估了北极内部、外部以及向北极输送的各类过程，分析了气候驱动与排放驱动的过程对北极PCB浓度的影响，以及这些过程对改善北极季节循环模拟效果的作用。研究发现，北极外部过程对北极大气PCB浓度的影响要大于北极内部过程。模拟结果显示，若要复现北极大气PCB的观测时间演变趋势，夏季海冰融化或北冰洋产生的再排放量需达到极不切实际的高水平。本研究最终得出结论：在全球变化情景下，中纬度过程对北极地区的影响要大于北极内部的再排放过程。