DRY DEPOSITION OF ATMOSPHERIC PARTICLES - APPLICATION OF CURRENT MODELS TO AMBIENT DATA

The dry deposition mass flux for atmospheric particles was calculated as a function of particle size (mass-flux size distribution). The mass-flux size distribution increased rapidly with particle size with the majority of the calculated flux due to particles larger than 1-mu-m (>90%). The evaluation of dry deposition was based on (1) atmospheric mass-size distributions between 0.01 and 100-mu-m diameter obtained from field measurements with a cascade impactor and a Noll rotary impactor (NRI) and data in the literature obtained with a wide-range aerosol classifier (WRAC) system, (2) field dry deposition sampling data using a surrogate surface, and (3) dry deposition calculations based on various models that estimate dry deposition velocity as a function of particle size. Results of model calculations using the atmospheric particle size distribution data were compared to measured flux data to show that realistic estimates can be made for the total dry deposition flux. Calculations using models that account for particle size distribution show that results are extremely sensitive to the mass of large particles and that large particles control dry deposition flux due to their high deposition velocities. Current dry deposition modeling techniques that use average particle concentrations and average deposition velocities underestimate the contribution of coarse particles to dry deposition and therefore underestimate dry deposition.