A Observation Study on the Scavenging of HCI and HNO_3 Vapor by Snow Particles

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For monitoring shapes of snow particles continuously and automatically, a simple device was developed. Two video cameras with different magnifying powers were used for distinguishing crystal shapes and degrees of riming as well as for distinguishing between aggregates and graupel particles. The visual field areas of the two cameras were 55x42 mm^2 and 9.2x7.0 mm^2, respectively. Snow particles which were collected on a clear Plexiglas disk were blown off by a blower that was operated at constant intervals. A fresh disk surface was then prepared for the next sampling of snow particles.Observations were carried out from January to March 1998 at Mitoi in a sparsely populated suburban area of Sapporo City. Falling snow particles were collected at intervals of approximately 1 hr. The shapes of snow particles and snowfall intensity were continuously monitored by the above device and a snow gauge using an electric balance, respectively. The concentrations of HCl and HNO_3 vapors in air were measured. It was assumed that these vapors contributed to the acidification of snow particles in riming growth as well as in vapor depositional growth ; but the concentrations of the vapors in air were low at our observation site. Also, it was thought that the vapors were scavenged by snow particles collected on January 1997 at Mosiri in a remote area. It was inferred that that the vapors scavenged by snow particles did not originate in the local urban polluted air but were carried with clouds.