Water insoluble dust particles in spring snow at Mt. Tateyma, Japan: Characteristics of their size distribution, shape factor and composition

摘要

The size distribution, shape factor and elemental composition of water insoluble particles in dirty snow layer at Murododaira (2450 m a. s. 1.) of Mt. Tateyama, Japan were analyzed by an optical microscope with a digital camera and a SEM/EDX system. Mono- or bi-modal size distribution of particles was identified. As fitted with the lognormal size distribution, the parameters for the predominant mode are number-median diameter between 0.77 and 2.23 μm with standard deviation (log σ) between 0.17 and 0.36. Coarser mode was also identified for one sample as the median diameter of 6.35 μm with log σ of 0.14. The median aspect ratio varies from 1.22 to 1.31. Little particles have the aspect ratio more than 2.5. The median circularity factor was from 0.83-0.97. More than 62% of particles have circularity factor in the range of 0.8-1. The figure of circularity factor verse diameter shows a triangle pattern and the figure of aspect ration verse shows a sector pattern. More than 90% of water insoluble particles were composed mainly Quartz and Aluminosilicates. Calcium was rarely detected in the particles because of the elution of water soluble Ca containing minerals. The parameters of size distribution, shape factor, elemental composition of the dusts in layer f were different from others. Backward air trajectory before the deposition suggests that the dust particles in layer f were originated from the Sahara.