Abstract
Wind-blown mineral particles were observed in the daytime on 5 February 1991 in Tsukuba, Japan. The time change in the number-size distribution of aerosol particles with radii between 0.15 and 5 μm were measured with an optical counter. Aerosol particles were collected on electron microscope grids with impactors to obtain the composition of individual particles by electron microscopy.
A meteorological investigation indicated that the local dust episode was generated in the daytime during a strong vertical mixing of air. The number-size distribution measured during the dust episode revealed concentrations of many coarse particles with radii of more than 1 μm. However, an electron microscopic examination indicated the presence of another mode of mineral particles in the radius range of less than 0.5 μm, together with the dominant mode of coarse mineral particles.
The lifting of mineral particles by a dust whirl is an important process in the generation of atmospheric mineral particles under strong horizontal wind velocities, as are saltation sandblasting and bombardment processes.
