Lidar measureme nts and airborne-particle collections were performed during KOSARP 87 (KOSA Research Program of Nagoya University; April-May 1987) at Nagoya (35°N, 137°E) to investigate the vertical distribution of Asian dust (KOSA) particles and the transport of these particles. The lidar measurements show that highly concentrated particle layers with a large depolarization ratio were frequently in the range from about 2 km to 6 km.
Electron microscope observations on the morphology of individual particles in a height range from near the ground to about 4400m suggest that the particle layers contained many soil particles.It is reasonable to consider that KOSA particles were very frequently transported from Asian desert areas to the islands of Japan in the middle troposphere, even when the effect of the KOSA was not detected near the ground. This 'background KOSA' has concentrations of about 1.9 - 25 μg/m3 at the layer peaks and one order of magnitude smaller than the values of severe KOSA. However, the contribution of 'weak KOSA' to the global budget of soil particles is not negligible since the frequency of occurrence of 'weak KOSA' is high. The reaction of soil particles sampled on the vapor-deposited Ca thin-film suggests that some of the particles were coated by water or a solution containing SO
42. Such particles can absorb various atmospheric gases and, therefore, the KOSA particles can play an important role in the geochemical cycle of many chemical constituents, as chemical reaction sites in the atmosphere and as carrier of chemical products.
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