The impact of volcanic gases from Miyake island on the chemical constituents in precipitation in the Tokyo metropolitan area

nss-SO42− concentrations in precipitation at the sampling sites in the Tokyo metropolitan area were 59.5-77.0 μeq/L during the degassing period, and 33.3-44.1 μeq/L during the normal period, respectively. The difference of nss-SO42− concentrations between the two periods was statistically significant. In contrast, no significant differences were observed in the concentrations of the other major ions (NH4+, nss-Ca2+, Cl−, and NO3−) between the two periods. The impact of volcanic degassing from Miyake Island on the ionic concentrations in the precipitation of the Tokyo metropolitan area was seen only in the H+ and nss-SO42− concentrations. The annual wet deposition amount of volcanic nss-SO42− into the Tokyo metropolitan area has been quantitatively estimated. The annual wet deposition amounts were calculated as 701±277 Meq/year (22.4±8.9 kt SO2/year) on the total area of the Tokyo metropolitan area (14,000 km2). The wet deposition amount of nss-SO42− corresponds to only 0.15% of the total annual amount of volcanic SO2 (15 Mt/year) emitted from Miyake Island from September 2000 to August 2001. This estimation is consistent with a previous study which reported that 0.3% of the atmospheric discharge of SO2 from the volcano in Mt. Etna in Sicily was deposited by precipitation to the surrounding area (1200 km2). The annual wet deposition amount of volcanic SO2 to the Tokyo metropolitan area was at the same order of the magnitude (37±15%) as the annual anthropogenic SO2 amount (60 kt/year) emitted from the Tokyo metropolitan area.