Wet and dry deposition of sulfur associated with the eruption of Miyakejima volcano, Japan

Abstract

Since July 2000 the activity of Miyakejima volcano has become brisk. Sulfur emitted from the volcano has flowed into the Japanese Archipelago and brought high‐concentration episodes of SO2 over a wide area. The daily average emission of SO2 during the period from August 2000 to March 2001 was the same level as the recent emission of SO2 originating from fossil fuel combustion in east Asia. Estimated total (wet plus dry) deposition of sulfur at Tanzawa before the eruption for the most remarkable high‐concentration episodes was almost the same level as the recent total deposition of sulfur over Japan. Estimated total deposition of sulfur after the eruption, on the other hand, was more than three times higher than the level before the eruption. The contribution of wet deposition increased with increasing daily precipitation amount, which indicates that precipitation scavenging had an instant effect in the removal of the volcanic sulfur. In the warm season, in which the subtropical high‐pressure system over the Pacific is dominant, high‐concentration episodes at monitoring stations were sometimes linked together with a time lag, which was explained by the fact that volcanic plumes from Miyakejima were transported north by the prevailing wind system in this season. In the cold season, however, the predominant wind system over the Japanese Archipelago is northwesterly from the Asian continent; most of the volcanic sulfur was thought to flow over the Pacific Ocean. Although no direct correspondence was found between the SO2 dry deposition and the SO2 emission, there was a close parallel temporal variation between the nss‐SO42− wet deposition and the SO2 emission. It was thought that the interaction between the precipitation cloud and the volcanic cloud took place just after the eruption of Miyakejima and that wet deposition plays an important role in the removal of the volcanic sulfur inflow outside the region.