三峡库区典型消落带多环芳烃大气-水界面交换通量与机制研究

Under the influence from the regular impoundment and discharge of water by Three Gorges Dam, the environmental geochemical cycle of pollutants in the water-level-fluctuation zone of Three Gorges Reservoir (TGR) has been changing, and as a consequence drawn intensive worldwide attention. Understanding the air-water exchange action of pollutants in the water-level-fluctuation zone of TGR is therefore significant to assess their regional geochemical cycle. In this study, based on the question that “Is the ‘absorption from the atmosphere’ or ‘evaporation from the water’ dominated for PAHs in the interface between atmosphere and surface water?”, a typical water-level-fluctuation zone, Pengxi river wetland natural protection area, was selected as a stationary site to conduct the sampling campaign. Four seasonal paired air and water samples (30 in each pair) were collected to investigate the concentration, composition, as well as air-water exchange flux and mechanism, of PAHs. This study could be the first attempt to explore the air-water interaction of PAHs and provide insightful environmental geochemical datasets of PAHs in TGR after the complete impoundment.

受三峡大坝蓄水放水的影响，三峡库区消落带污染物环境地球化学过程随之发生变化，已成为国内外研究者关注的焦点。本课题围绕典型持久性有机污染物多环芳烃（PAHs）在库区消落带不同水、气条件影响下水-气交换过程是“由大气向水体输入为主（吸收），还是由水体向大气释放为主（挥发）”这一重要科学问题，选择库区典型消落带-澎溪河湿地自然保护区作为观测点，通过季节性采集大气和水体样品，估算PAHs水-气交换通量，揭示季节性“吸收-挥发”转换作用与机制。本研究是三峡大坝蓄水完成后关于三峡水库PAHs水-气相互作用的首次探索，提供了PAHs在库区大气和水体界面中环境行为的基本数据，对于深入认识三峡库区蓄水放水期间PAHs环境地球化学行为具有重要科学意义。

受三峡大坝蓄水放水的影响，三峡库区消落带污染物环境地球化学过程随之发生变化，已成为国内外研究者关注的焦点。本课题选择库区典型消落带-澎溪河湿地自然保护区作为观测点，通过季节性采集大气PM2.5样品，揭示不同水位条件下PAHs来源，估计水-气潜在交换趋势。于2017年和2018年采集了39个PM2.5样本，22个样品为2017年8月采集（低水位〜135m），17个样品为2018年1月采集（高水位〜175m）。系统分析了有机碳（OC）,元素碳（EC）,char-EC（char）,Soot-EC（soot）,16种PAHs浓度水平以及藿烷和甾烷的相对丰度。OC，EC，Char，Soot, 16 PAHs高水位条件下平均浓度分别为：9.17µg/m3，4.69 µg/m3，4.25µg/m3，0.45 µg/m3，17.42 ng/m3）,低水位条件分别为6.55µg/m3、1.70 µg/m3、1.37µg/m3、0.32µg/m3、5.60 ng/m3。特征分子比例法显示在低水位时空气-土壤/植物交换是2-3环PAHs的来源，在高水位时生物质燃烧则是4-5环的来源。藿烷和甾烷的比例特征和相对丰度显示木材燃烧、机动车尾气和成熟石油残留的混合来源。本研究是三峡大坝蓄水完成后关于三峡水库不同水位条件下PAHs来源解析和水-气交换的首次探索，提供了PAHs在库区大气和水体界面中环境行为的基本数据，对于深入认识三峡库区蓄水放水期间PAHs环境地球化学行为具有重要科学意义。