Su Yushan, Wania Frank
Department of Chemical Engineering and Applied Chemistry, University of Toronto at Scarborough, Toronto, Ontario, Canada.
Environ Sci Technol. 2005 Sep 15;39(18):7185-93. doi: 10.1021/es0481979.
Forests act as efficient filters for many airborne semivolatile organic compounds (SOCs). However, most simulations of an organic chemical's long-range transport in the atmosphere do not account for this filter effect. In this study, forests are introduced into an existing zonally averaged global distribution model (Globo-POP) to investigate how such a change affects a chemical's potential to undergo long range transport and accumulation in the Arctic, as quantified by the Arctic contamination potential (ACP). Simulation results indicate that the ACP of a "space" of perfectly persistent hypothetical organic chemicals, defined by log KOA and log KAW, is reduced by introducing forests in the global model. Depending on partition characteristics, this reduction can be as large as a factor of 2. Model calculations also indicate that it is mostly the boreal forests, specifically boreal deciduous forests, which play a key role in this respect. Sensitivity analyses establish the deposition velocity to boreal forests, especially for gaseous compounds, as one of the most influential parameters controlling this global forest filter effect. The extent of the effect is further sensitive to the forest density and precipitation rate in the boreal zone, and the degradation rates of the chemical. Specifically, degradation in the forest canopy may enhance the effect and further reduce an SOC's long range transport to remote regions. Simulations for three PCB congeners suggest that forests may reduce concentrations in air, ocean, and freshwater at the expense of increased concentrations in forest soils and may lead to substantially increased overall global residence times.
森林对许多大气中的半挥发性有机化合物（SOCs）起到高效过滤器的作用。然而，大多数关于有机化学品在大气中长距离传输的模拟并未考虑这种过滤效应。在本研究中，将森林引入现有的纬向平均全球分布模型（Globo - POP），以研究这种变化如何影响化学品在北极进行长距离传输和积累的潜力，这一潜力通过北极污染潜力（ACP）来量化。模拟结果表明，在全球模型中引入森林后，由log KOA和log KAW定义的完全持久性假设有机化学品“空间”的ACP降低。根据分配特性，这种降低幅度可达2倍。模型计算还表明，在这方面起关键作用的主要是北方森林，特别是北方落叶林。敏感性分析确定了北方森林的沉积速度，尤其是气态化合物的沉积速度，是控制这种全球森林过滤效应的最有影响力的参数之一。这种效应的程度还对北方地区的森林密度、降水率以及化学品的降解速率敏感。具体而言，森林冠层中的降解可能会增强这种效应，并进一步减少SOC向偏远地区的长距离传输。对三种多氯联苯同系物的模拟表明，森林可能会降低空气、海洋和淡水中的浓度，但代价是森林土壤中的浓度增加，并且可能导致全球总体停留时间大幅增加。
