持久性有机污染物气—土界面交换研究进展

Research progress on exchange of persistent organic pollutants at the air-soil interface

气—土界面交换对于持久性有机污染物(POPs)在区域和全球尺度上的传输迁移、重新分布和归趋具有重要意义。气—土界面交换所涉及的过程主要包括:干沉降、湿沉降和从土壤向大气的挥发。其中,气态化合物的扩散交换是决定"源和汇"的关键过程。气态化合物在气—土界面的交换过程由大气和土壤之间的浓度梯度驱动,土—气分配主要受化合物理化性质、温度和土壤有机质的影响。随着全球POPs禁用进程的加快,中纬度污染地区的土壤逐渐成为低分子量化合物向大气排放的二次源;而对于高分子量的化合物来说,土壤仍然是污染物的汇,可以存储更多的污染物。气—土交换方向还受到温度的影响,呈现出土壤夏季为源、冬季为汇的季节性变化特点。逸度模型是估算POPs气—土交换通量的有力工具,由通量大小可以定量判断源和汇的强度。此外,还讨论了目前POPs气—土界面交换研究中存在着的一些不足,并提出该领域未来可能的发展趋势。

Exchanges at the air-soil surface play an important role in controlling the regional and global transport, redistribution and fate of POPs. The main processes contributing to the exchanges at air-soil interface are wet deposition, dry deposition and volatilization from the soil. Furthermore, the diffusive exchange of POPs is the key process affecting the matter of ＂source or sink＂. Diffusive exchange between air and soil is driven by the concentration gradient between air and soil. Soil-air partitioning is mainly dependent on physical and chemical properties of compounds, temperature and soil organic matter. As the production of most POPs has been banned in many countries after 1980s, the soil of mid-latitude area is gradually becoming a secondary source of the lighter molecular weight compounds to the atmosphere and a sink for the heavier ones. Air-soil exchange direction is affected by temperature and shows a seasonal trend such that soil is a source in summer and a sink in winter. Fugacity model is a powerful tool to estimate the air-soil exchange fluxes quantitatively. This paper reviewed the research progress on the above-mentioned scientific topics, pointed out the research areas that need more focus, and made suggestions for further studies.