Dastoor Ashu P, Davignon Didier, Theys Nicolas, Van Roozendael Michel, Steffen Alexandra, Ariya Parisa A
Air Quality Research Division, Science and Technology Branch, Environment Canada, 2121 Trans Canada Highway, Dorval, Quebec, Canada H9P 1J3.
Environ Sci Technol. 2008 Jul 15;42(14):5183-8. doi: 10.1021/es800291w.
At polar sunrise, gaseous elemental mercury (GEM) undergoes an exceptional dynamic exchange in the air and at the snow surface during which GEM can be rapidly removed from the atmosphere (the so-called atmospheric mercury depletion events (AMDEs)) as well as re-emitted from the snow within a few hours to days in the Polar Regions. Although high concentrations of total mercury in snow following AMDEs is well documented, there is very little data available on the redox transformation processes of mercury in the snow and the fluxes of mercury at the air/snow interface. Therefore, the net gain of mercury in the Polar Regions as a result of AMDEs is still an open question. We developed a new version of the global mercury model, GRAHM, which includes for the first time bidirectional surface exchange of GEM in Polar Regions in spring and summer by developing schemes for mercury halogen oxidation, deposition, and re-emission. Also for the first time, GOME satellite data-derived boundary layer concentrations of BrO have been used in a global mercury model for representation of halogen mercury chemistry. Comparison of model simulated and measured atmospheric concentrations of GEM at Alert, Canada, for 3 years (2002-2004) shows the model's capability in simulating the rapid cycling of mercury during and after AMDEs. Brooks et al. (1) measured mercury deposition, reemission, and net surface gain fluxes of mercury at Barrow, AK, during an intensive measurement campaign for a 2 week period in spring (March 25 to April 7, 2003). They reported 1.7, 1.0 +/- 0.2, and 0.7 +/- 0.2 microg m(-2) deposition, re-emission, and net surface gain, respectively. Using the optimal configuration of the model, we estimated 1.8 microg m(-2) deposition, 1.0 microg m(-2) re-emission, and 0.8 microg m(-2) net surface gain of mercury for the same time period at Barrow. The estimated net annual accumulation of mercury within the Arctic Circle north of 66.5 degrees is approximately 174 t with +/-7 t of interannual variability for 2002-2004 using the optimal configuration. We estimated the uncertainty of the model results to the Hg/Br reaction rate coefficient to be approximately 6%. Springtime is clearly demonstrated as the most active period of mercury exchanges and net surface gain (approximately 46% of annual accumulation) in the Arctic.
在极地日出时，气态单质汞（GEM）在空气和雪面之间会发生异常的动态交换，在此期间，GEM能够迅速从大气中被去除（即所谓的大气汞消耗事件（AMDEs）），同时在极地地区，它也能在数小时至数天内从雪中重新释放回大气。尽管AMDEs之后雪中总汞的高浓度已有充分记录，但关于雪中汞的氧化还原转化过程以及气/雪界面处汞通量的数据却非常少。因此，AMDEs导致的极地地区汞的净增加量仍是一个悬而未决的问题。我们开发了一个新版本的全球汞模型GRAHM，该模型首次通过制定汞卤素氧化、沉降和重新释放的方案，纳入了春季和夏季极地地区GEM的双向表面交换。同样也是首次，利用GOME卫星数据得出的BrO边界层浓度被用于全球汞模型中，以呈现卤素汞化学过程。对加拿大阿勒特地区2002 - 2004年3年期间模型模拟和实测的大气GEM浓度进行比较，结果显示该模型能够模拟AMDEs期间及之后汞的快速循环。布鲁克斯等人（1）在2003年春季为期2周的强化测量活动（3月25日至4月7日）中，测量了阿拉斯加巴罗地区汞的沉降、重新释放以及汞的净表面增加通量。他们报告的沉降、重新释放以及净表面增加通量分别为1.7、1.0±0.2和0.7±0.2 μg m⁻²。使用该模型的最佳配置，我们估算出同一时期巴罗地区汞的沉降通量为1.8 μg m⁻²，重新释放通量为1.0 μg m⁻²，净表面增加通量为0.8 μg m⁻²。使用最佳配置估算得出，2002 - 2004年北极圈以北66.5度范围内汞的年净积累量约为174吨，年际变化为±7吨。我们估算出模型结果对于汞/溴反应速率系数的不确定性约为6%。春季显然是北极地区汞交换和净表面增加最为活跃的时期（约占年积累量的46%）。
