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

为了连续、自动地监测雪粒的形状，研制了一种简单的装置。用两个不同放大倍率的摄像机来区分晶体形状和边缘程度，以及区分聚集体和霰颗粒。两台相机的视野面积分别为55x42 mm^2和9.2x7.0 mm^2。收集在透明的有机玻璃圆盘上的雪颗粒由一个以恒定间隔操作的鼓风机吹走。然后准备一个新的圆盘表面，以进行下一次的雪颗粒采样。1998年1月至3月在札幌市一个人口稀少的郊区的Mitoi进行了观测。每隔大约1小时收集一次降雪颗粒。利用上述装置和电天平测雪仪，分别连续监测雪粒形状和降雪强度。测定了空气中HCl和HNO_3蒸气的浓度。假定这些蒸汽在水雾生长和气相沉积生长过程中对雪颗粒的酸化起了作用；但在我们的观察点，空气中蒸汽的浓度很低。此外，人们还认为，1997年1月在偏远地区Mosiri收集的雪颗粒清除了这些蒸汽。由此推断，被雪颗粒清除的水汽并非来源于当地城市污染空气，而是由云层携带而来。

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.