Distribution of Deposition of Non-sea-salt Sulfate and its Mass Balance Around Chyugoku Mountainous Area

Abstract

Wintertime atmospheric concentration of NSS-sulfate and SO₂ and fallout amount of NSS-sulfate were measured at 5 sites placed along the stream of NW monsoon, which blew over Chyugoku mountain. Rain and snow were classified to NW monsoon type and the other type based on the cause of rain and snow. In the case of NW monsoon type, peaks of fallout amount of many components existed just before the mountain, where air was going upwards. On the other hand, in the other cases, fallout amount was higher at the coast and mountain top than at the foot of the mountain. From the viewpoint of washout ratio, it was estimated that the place, where air was going upwards, had a higher washout ratio due to the acceleration by effective rainout.
Mass balance of total sulfur compounds was estimated from December 22 to 25 in 1992 as a model case. According to this calculation, about 14% of total atmospheric sulfur compounds was removed by the precipitation, while air passed over the mountain, which meant that bout 2% of sulfur compounds was removed by 10 km. The contribution of washout under the altitutde of 1000 m to the total fallout was estimated 68% in the plain area and under 35% in the mountainous area.