Record of Pre-neutralized H_2SO_4 Implied in the Results of Four-Stage and Five-Stage Paralleled Filter Pack Observations on the Western Edge of Japan

摘要

Particulate sulfate (SO_4~(2-) ) usually exists in the atmosphere in the chemical form of (NH_4)_2SO_4 and/or NH_4HSO_4. In contrast, we could successfully detect particulate sulfuric acid (H_2SO_4) without neutralization by ammonia in the monitoring campaign by filter pack methods. The presence of ambient H_2SO_4 was revealed from the concentration difference in a nitric acid gas (HNO_3) determined by a four-stage filter pack and a five-stage filter pack. Ambient H_2SO_4 could exist more frequently in summer (August) than in winter (January). Trajectory analysis identified the attribution of ambient H_2SO_4 as follows: in summer, SO_2 released from a domestic volcano in Japan was responsible for the ambient H_2SO_4, while in other seasons, SO_2 was carried to the survey site by northwestern air masses from the Asian continent.