三峡库区典型消落带冬季多环芳烃大气-植物/土壤交换过程与通量

三峡大坝每年周期性“蓄水-放水”,形成水位落差巨大的消落带,库区内污染物环境地球化学行为随之发生变化.以冬季淹没期消落带多环芳烃为研究对象,采集成对大气（n=16）、植物（n=12）和土壤样品（n=12）,采用气相色谱/质谱法（GC/MS）,分析USEPA 16PAHs浓度水平,解析来源,估算大气-地表、大气-植物等多介质交换通量.结果表明：大气、土壤和植物中PAHs浓度为5.65~13.47ng/m³、70.86~135.44ng/g和78.23~1084.72ng/g,平均值分别为（8.58±2.78） ng/m³、（90.10±22.18） ng/g和（360.36±309.54） ng/g.大气中PAHs以2~3环为主（62.3%）,植物中PAHs以3~4环为主（73.7%）,土壤中PAHs以3环和5环为主（52.1%）.特征分子比值法揭示煤、生物质燃烧是植物PAHs的主要来源,以石油为主的化石燃料燃烧是大气和土壤PAHs主要来源.“一室模型”表明,植物吸收PAHs的主要途径为植物-气相之间动态平衡限制下的气沉降.“逸度模型”表明,3环和4环PAHs气-土交换通量分别为-19.20和-0.14,主要是从土壤向大气挥发,5~6环PAHs气-土交换通量为0.89,主要是由大气向土壤沉降.大气中颗粒态PAHs干沉降通量为293.35~833.61ng/m²·d,平均值为517.82ng/（m²·d）,以5~6环（59.02%）为主.本研究探讨了冬季PAH多介质交换过程,揭示了植物和土壤对于不同单体的吸收和沉降角色,为进一步研究库区不同季节PAH环境地球化学循环提供基础数据.

Air-plant/soil exchange process and flux of polycyclic aromatic hydrocarbons in winter in the typical water-level-fluctuation zone of the Three Gorges Reservoir region,China

Affected by the seasonal "storage-discharge" of the Three Gorges Dam, the water level fluctuation zone (WLFZ) of the Three Gorges Reservoir Region (TGRR) show a periodic change of "submergence-exposure" each year, and the environmental geochemical processes of organic matter in this area changed accordingly. This study took polycyclic aromatic hydrocarbons (PAHs) as the targeted compounds. The coupled air, plant and soil samples (n=40) were consecutively collected. These samples were analyzed for USEPA 16PAHs to explore their composition characters and estimate the air-plant/soil exchange flux. The concentration of PAHs in air, soil and plants were 5.65~13.47ng/m³, 70.86~135.44ng/g, 78.23~1084.72ng/g, with an average of (8.58±2.78) ng/m³, (90.10±22.18) ng/g and (360.36±309.54) ng/g respectively. 2 to 3 ring PAHs dominated in the air, contributing 62.3% of the total. 3 to 4 ring PAHs dominated in plants, with a contribution of 73.3%. 3 and 5 ring PAHs in dominated soil, accounting for 52.1% of the total. The molecular diagnostic ratio of PAHs indicated that petroleum could be the main source of PAHs in plant. Biomass and fossil fuel combustion were the main sources of PAHs in air and soil. "One-compartment model" indicated that the main way for plants to absorb PAHs was gaseous deposition which was restricted by the plant-gas dynamic equilibrium. The fugacity model showed that the air-soil exchange flux of 3-ring, 4-ring and 5~6-rings PAHs were -19.20, -0.14 and 0.89, respectively. 3~4rings PAHs in the soil were mainly re-volatile into the atmosphere, while 5~6 rings in the atmosphere mainly deposited into the soil. The dry deposition flux of PAHs was between 293.35 and 833.61ng/(m²·d), with an average of 517.82ng/(m²·d) and dominated by 5~6 rings (59.02%). As investigating the multi-medium exchange process of PAHs in winter, this study could reveal the absorption and deposition role of different monomial PAHs by plants and soil. These datasets provide important basis for further study on environmental geochemical cycle of PAHs in different seasons in the TGRR.