大気中二酸化硫黄のエアロゾルへの変換

抄録

During 168hr from 26 July to 2 August, 1977, simultaneous measurements of gaseous and particulate sulfur concentrations in the atmosphere were made at three observation sites which are located nearly in a straight line along the Yodo River. Distances between the sites are about 10 km. The variation of particulate sulfur concentration had a period of 24hr due to the alternation of sea and land breezes, and the variation patterns at the three sites were quite similar. The concentration peak appeared about one hour later at the leeward station than at the windward station in accordance with the movement of polluted air parcel. The average concentrations of particulate sulfur observed at the three sites were found to be nearly equal. Contrary to this, average concentrations of gaseous sulfur decreased from windward to leeward in the sea breeze time. It appears that the main variation of SO₂ gas concentration was similar to that of particulate sulfur concentration of one day period and this was superposed by a small variation which had also one day period and lagged in phase by 8 to 12hr. Using a simple transport and diffusion model, the conversion rate of SO₂ gas to sulfur particulate was calculated from the observational results taking the wind system into consideration. As expected, the conversion rate was high at the time of large insolation. The maximum of the observed values was about 20%/hr. Furthermore, a good correlation was found between the conversion rate and the oxidant concentration.