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[B-1.3. Studies on formation and loss processes of SO₃ for a model including aerosol production]

[Contact Person]

Takashi Imamura
Head
Ozone Layer Research Team
Global Environmental Research Group
National Institute for Environmental Studies
Environment Agency
16-2 Onogawa, Tsukuba, Ibaraki 305-0053, Japan
Phone: +81-298-50-2406, Fax: +81-298-50-2579
E mail:imamura@nies.go.jp

[Total Budget for FYl997-FYl999]

31,625,000 Yen (FY1999:10,492,000 Yen)

[Abstract]

      Two types of experiments have been performed; i.e., rate measurements of the elementary processes and chamber experiments, to elucidate the mechanisms and to quantify the efficiencies of the photooxidation of reduced sulfur compounds.
      Rates of oxidation reactions of SO, CH₃S, and HS radicals by peroxy radicals were measured for the first time by means of time-resolved photoionization mass spectrometry combined with pulsed-laser photolysis. It was found that all of the radicals -investigated in this project could react with CH₃O₂ radicals rapidly with rate constant of ca. 10^-10 cm³molecule^-1s^-1. This suggests that peroxy radicals can promote the oxidation of these sulfur-containing radicals.
      The yield of SO₂ formation from the photooxidation of CH₃SCH₃ was measured as a function of the NOx concentration and temperature. It was found that the SO₂ yield increased with increasing temperature and with decreasing the concentration of NOx. The experimental results could be explained in terms of the temperature dependent reactions of CH₃SO₂.

[Key Words]

Reduced sulfur compound, Oxidation process, Peroxy radical, reaction rate constant, SO₂ formation yield