Water-insoluble particles in spring snow at Mt. Tateyama, Japan: Characteristics of the shape factors and size distribution in relation with their origin and transportation

Abstract

The number-size distribution and shape factors of water-insoluble particles (WIP) in four dirty snow layers in the spring of 2001 at Mt. Tateyama, Japan, were analyzed using scanning electron microscopy, and using optical microscopy with a digital camera. Results show that the median aspect ratio (ratio of the longest dimension b to the orthogonal width a; b/a) of the WIP varied within 1.22-1.31. Only a few particles with an aspect ratio of more than 2.5 were observed. The median circularity factor (4πS/l2; S is projection area, and l is periphery length) varied from 0.83-0.97. Combined with backward air trajectories, visibility reducing surface weather reports, additional results of rain containing Saharan dust and dry deposition samples, the number and shape factor distributions versus particle size were characterized as (1) narrower distributions of number-size and shape factors for the Saharan dust, and (2) bi-modal number-size distribution for dry deposited dust. Results suggest that the proportions of nearly spherical (higher circularity nearly 1) and less elongated (lower aspect ratio close to 1) particles were higher in the sample that had been transported a longer distance from the dust source areas. © 2007, Meteorological Society of Japan.