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Measurements of aerosol size-separated number concentrations were performed in March 2001 on the Tama Hills of Japan, located near regions of heavy industry. The concentrations of particles larger than 1.0 µm in diameter dramatically increased during the Kosa phenomena on 6-8 and 18-24 March. The number concentrations of coarse particles (>3.0 µm) showed distinct diurnal variations, especially during the Kosa events. Fine particles smaller than 0.5 µm increased when the relative humidity was high and the wind speed was low. On the other hand, the coarse particles concentrations were well correlated with wind speed and temperature. The dry deposition velocity of the coarse particles at the forest canopy was estimated from the nighttime decrease in the number concentrations.

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