A. Wet and Dry Deposition, Including Melting Phenomena and Snowpack Chemistry
The session began with a review by D. Fowler of the mechanisms of wet and dry deposition of sulphur and nitrogen compounds. Wet deposition, which includes rainout and washout, is often parameterized by a washout ratio (concentration in cloud droplets or in precipitation divided by the concentration in air). Dry deposition, which includes the fallout and impaction of particles and the absorption of gases at the surface of the earth, is often parameterized by a deposition velocity, which is a function of both meteorological and biological factors. Dr. Fowler emphasized the uncertainties that surround the practical application of these concepts to determining deposition rates, but nevertheless provided a useful table of typical deposition rates. The table shows the dominance of dry deposition close to source areas, and the increasing contribution made by wet deposition with increasing downwind distance.
KeywordsDeposition Rate Deposition Velocity Cloud Droplet Supercooled Water Washout Ratio
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