Modeling the dry deposition velocity of sulfur dioxide and sulfate in Asia

The dry deposition model was created to estimate SO2 and sulfate dry deposition velocities over nine land use types in Asia. The study domain is 20°S-50°N, 39°-154°E. Monthly averaged 1°×1° dry deposition velocities are estimated for four seasons. Model results show that the dry deposition velocity of SO2 demonstrates strong seasonal and diurnal variability in summer, fall, and spring. In summer, the daytime velocity (in centimeters per second) for SO2 forests is 0.4, over cultivation is 0.2, grassland is 0.5, and ocean is 0.8. Nighttime values of SO2 are two or three times less than daytime values. In winter, the deposition velocity of SO2 does not show much diurnal variability-the value is 0.1-0.2 except over ocean, when it is 0.5. Contrary to SO2, the dry deposition velocity of sulfate only slightly varies with seasons and time of the day. Generally, its value is less than 0.1.