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

为实现雪粒形状的连续自动监测，研制了一种简易的雪粒形状监测装置。用两台放大倍数不同的摄像机来区分晶体的形状和结晶程度，以及区分聚集体和谷粒。两台摄像机的视野面积分别为55x42 mm^2和9.2x7.0 mm^2。收集在透明树脂玻璃盘上的雪颗粒由以恒定间隔操作的鼓风机吹走。1998年1月至3月，在札幌市人口稀少的郊区Mitoi进行了观测。每隔约1小时收集一次落下的雪粒，分别用上述装置和使用电子天平的雪量计连续监测雪粒的形状和降雪强度。测定了空气中HCl和HNO_3蒸气的浓度。据推测，这些蒸汽有助于酸化的雪粒子在雾凇的增长，以及在蒸汽沉积的增长，但在我们的观测点的空气中的蒸汽浓度低。此外，人们认为这些蒸汽是1997年1月在偏远地区的Mosiri收集的雪粒清除的。据推测，被雪颗粒清除的蒸汽不是来自当地城市污染的空气，而是被云带走的。

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.