Effects of Dry Deposition on Near-Surface Concentrations of SO2during Medium-Range Transport

Abstract

The method for estimating dry deposition velocity using local routine surface measurements with some empirical constants used in the Regional Acid Deposition Model is developed and implemented to the Lagrangian particle dispersion model to more accurately estimate near-surface concentrations of the SO₂ pollutant. A test is performed for the synoptic case of a weak westerly geostrophic wind at 850 hPa with the cloud amount of less than 5/10. Hourly surface data from 64 sites located in South Korea are hourly averaged for five spring seasons from 1989 to 1993 for the chosen synoptic situation and used to construct 3D meteorological fields and turbulent fields in the boundary layer. The dry deposition velocity of SO₂ estimated by the present model ranges from 0.01 to 1.4 cm s⁻¹ with relatively large values in the daytime. The estimated near-surface concentrations at the height of 1.5 m above the ground through the Lagrangian particle dispersion model including the effect of dry deposition indicate that the impact of the dry deposition on the near-surface concentration is significant during the day when the convective turbulent intensity is strong and the deposition velocity is large. The maximum reduction of the near-surface concentration due to the dry deposition process is more than 10% of the estimated concentration with the perfect reflection of the Lagrangian particle at the surface within 70 km in the downwind direction from the source during the daytime, while less than 5% reduction occurs within 50 km from the source during the night.