Effects of Miyake volcanic effluents on airborne particles and precipitation in central Japan

Abstract

Miyake volcano, which is located in the northwest Pacific Ocean 200 km south of the Tokyo metropolitan area, began to erupt on 8 July 2000. Its SO 2 emission amounted to a maximum of 6 × 10 4 t d −1 , which was about the same level as the anthropogenic emission of northeast Asia and 20 times larger than that of Japan, and is decreasing to 10 4 t d −1 . Aerosol and precipitation, together with gaseous pollutants, have been observed from 2 years before the eruption to present on a prominent mountain ridge, Happo ridge (330 km north of the volcano). Short time samplings of aerosols and gaseous acids, such as HCl and HNO 3 , were made for 3–6 hours every day. Annual mean concentration of SO 2 was increased 3.8 times, and concentrations of SO 4 2− were increased 1.5 and 1.7 times in aerosol and precipitation, respectively. In contrast, aerosol concentrations of NO 3 − and Cl − decreased under the influence of volcanic effluents. This was caused by the excess amount of SO 4 2− formation. The produced SO 4 2− at first exhausted gaseous ammonia to form (NH 4 ) 2 SO 4 aerosol and then, driving out NO 3 − and Cl − , it took their place in the aerosol and sometimes existed as sulfuric acid mist after exhausting ammonia. These facts were explained successfully by a multicomponent gas‐aerosol equilibrium. The expelled HNO 3 and HCl might be deposited more intensively both by wet and dry deposition processes and might accelerate the environmental acidification.