DRY DEPOSITION MODELING OF NITRATE AND SULFATE BY USING PARTICLE-SIZEDISTRIBUTION DATA

Dry deposition and air sampling were undertaken simultaneously in the ambient air of Ping Tung area by using several dry deposition plates, two MOUDIs (Micro-orifice Uniform Deposit Impactors) and one NRI (Noll Rotary Impactor) from December 1995 to May 1996 in Southern Taiwan. T he NRI and MOUDI were used to collect ambient coarse and fine particul ate, respectively. Dry deposition plate was applied to collect particl e deposition flux. An ion chromatography (Diones 2000i/SP) equipped wi th 4 mm AG4A-SC and AS4A-SC column was employed to analyze the anion s pecies (NO3- and SO42-). The eluent solution is 1.8 mM sodium carbonat e/ 1.7mM sodium bicarbonate. The calculated dry deposition flux for ea ch particle size range was obtained by using measured mass-size distri bution data between 0.18 and 100 mu m diameter and a dry deposition mo del. The mean modeled/measured (Md/ Ma) ratio of dry deposition flux v aried between 1.11 and 1.28, between 1.28 and 1.42 and between 0.88 an d 0.97 for nitrate, sulfate and total particle mass, respectively. The results indicated that nitrate and sulfate were slightly overestimate d by a dry deposition model, while total particle mass was slightly un derestimated by this model. In general, by using the particle size dis tribution data, this dry deposition model can provide a good predicati on for the dry deposition flux of nitrate, sulfate and total particle mass. More than 87.5 % of nitrate and more than 92.9 % of sulfate dry deposition flux are contributed by particle diameters larger than 10 m u m. This is due to the fact that particle size larger than 10 pm have higher dry deposition velocities (>4.65 cm/ sec) and control the majo rity of the dry deposition flux.