| Research Abstract |
Simultaneous sampling of chlorinated hydrocarbons(CHs) and monocyclic aromatic hydrocarbons(MAHs), which could be harmful to humans and/or responsible for the formation of ozone and secondary particles, in dew and rainwater and in the ambient air was performed from 2004 to 2006 in Hino City, which is located in western part of Tokyo, Japan. CHs were less contained in dew water than MAHs. Toluene(volume-weighted mean concentration, VWM : 4.77nM, sample number, n=49) and m, p-Xylene(VWM : 5.07nM, n=49) except dichloromethane, which was abnormally high(VWM : 1.14μM, n=49), were abundant among eleven VOCs determined in dew water. Chloroform, carbon tetrachloride, 1, 2-dichloroethane, and benzene were not detected in dew water during the study period. Dew and rainwater contained higher amounts of VOCs than would have been expected from the ambient gas-phase concentrations and the temperature-corrected Henry's law constants. Following the determination method of humic substances in river wat
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er proposed by Hiraide, et. al.(1994), the VWM of soluble humic and fluvic acid fractions in dew water was found to be 1.00mg/L and 0.87mg/L(n=20), respectively, while the VWM of particulate humic and fluvic acid fractions was found to be 0.61mg/L and 0.42mg/L(n=20), respectively. Surface tension decreased with the increase of dissolved fulvic acid fraction in dew water, indicating that humic-like substances with relatively lower molecular weight, which is soluble in acid solution, could be effective surface-active species within dew water. The enrichment factors, which were defined as the ratio of the observed VOCs concentration to the estimated, were over 10^2 for MAHs except benzene and increased as the increment of total HULIS concentration(the sum of humic and fulvic acid fractions in both dissolved and particulate form) normalized by total inorganic ion concentration in dew water. Our results indicate that total HULIS, i.e. both humic and fulvic acid fractions present in both dissolved and particulate form, in dew water could enhance the dissolution of atmospheric VOCs into dew droplets. Less
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