東広島における大気エアロゾル抽出水中のヒドロキシルラジカルの光化学的生成および消失機構

概要

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In order to identify sources and sinks of hydroxyl radical (^・OH) existing in atmospheric aerosols, we measured photochemical formation rates, scavenging rate constants and steady-state concentrations of ^・OH in water-extracts of atmospheric aerosols collected during August 2003 to May 2007 in Higashi-Hiroshima, Hiroshima Prefecture, Japan. Aerosol samples (n = 41) were collected using a low volume air sampler and extracted with pure water. ^・OH photoformation rates normalized by air-volume were in range of 0.02 to 1.91 nmol h^<-1> m^<-3> (mean = 0.33 nmol h<-1> m<-3>). The photo-Fenton reaction was a dominant source of ^・OH, which accounted for 49% (mean) of total ^・OH photoformation. Unidentified sources that were accounted for 33% (mean) could be organic compounds, such as humic-like substances, estimated by analysis of absorbance and 3D-excitation and emission matrix of the water-extract. Ranges of scavenging rate constants and steady-state concentrations of ^・OH determined were (0.89-4.5) × 10^5 s^<-1> and (2.6-13)×10^<-16> M, respectively, in the water-extracts. Inorganic compounds such as chloride were minor scavengers (mean = 1%) and organic compounds would be major sinks. These results suggested that photoformed ^・OH could play a major role in aqueous phase oxidation of organic matter occurring in atmospheric aerosol.
2009-03-30