Abstract：
The fate of volatile organic compounds (VOC) vapors in the unsaturated zone is the basis for evaluating the natural attenuation potential and vapor intrusion risk. Microcosm and column experiments were conducted to study the effects chemical speciation and soil types/properties on the fate of petroleum VOCs in unsaturated zone. The biodegradation and total attenuation rates of the seven VOCs obtained by microcosm experiments in black soil and yellow earth were also generally higher than those in floodplain soil, lateritic red earth, and quartz sand. The VOC vapors in floodplain soil, lateritic red earth, and quartz sand showed slow total attenuation rates (<0.3 d-1). N-pentane, methylcyclopentane, and methylcyclohexane showed lower biodegradation rates than octane and three monoaromatic hydrocarbons. Volatilization into the atmosphere and biodegradation are two important natural attenuation paths for VOCs in unsaturated soil columns. The volatilization loss fractions of different volatile hydrocarbons in all five unsaturated soils were generally in the order: n-pentane (93.5%-97.8%) > methylcyclopentane (77.2%-85.5%) > methylcyclohexane (53.5%-69.2%) > benzene (17.1%-73.3%) > toluene (0-45.7%) > octane (1.9%-34.2%) > m-xylene (0-5.7%). The fractions by volatilization into the atmosphere of all seven hydrocarbons in quartz sand, lateritic red earth, and floodplain soil were close and higher compared to the yellow earth and black soil. Overall, this study illustrated the important roles chemical speciation and soil properties in determining the vapor-phase transport and natural attenuation of VOCs in the unsaturated zone.
摘要：
不饱和区中挥发性有机化合物（VOC）蒸气的命运是评估自然衰减潜力和蒸气侵入风险的基础。进行了微观世界和柱实验，以研究化学形态和土壤类型/性质对非饱和区石油VOCs命运的影响。微观世界实验得到的7种VOCs在黑土和黄土中的生物降解率和总衰减率也普遍高于洪泛区土壤,红土红土,还有石英砂.洪泛区土壤中的VOC蒸气，红土红土,和石英砂表现出缓慢的总衰减率(<0.3d-1)。正戊烷,甲基环戊烷,和甲基环己烷的生物降解速率低于辛烷和三种单芳烃。挥发进入大气和生物降解是非饱和土柱中挥发性有机化合物的两条重要自然衰减路径。5种非饱和土壤中不同挥发性烃的挥发损失分数一般依次为:正戊烷(93.5%-97.8%)>甲基环戊烷(77.2%-85.5%)>甲基环己烷(53.5%-69.2%)>苯(17.1%-73.3%)>甲苯(0-45.7%)>辛烷(1.9%-34.2%)>间二甲苯(0-5.7%)。石英砂中所有七种碳氢化合物挥发到大气中的馏分，红土红土,与黄土和黑土相比，洪泛区土壤接近且较高。总的来说,这项研究说明了化学形态和土壤特性在确定非饱和区VOCs的气相传输和自然衰减中的重要作用。
