Study on Dry Deposition Mechanism using Representative Surfaces

II. Distinction of Dry Deposition Process among Gaseous and Particulate Matters using Dry, Acidic^-, Alkaline^-and water Surfaces as surrogate surfaces

Abstract

A dry Petri dish and Petri dishes filled with water, acidic water and alkaline water, were used for representative surfaces to measure deposition of dry components in environment air. These representative surfaces were established at each center of wide coarse surfaces, to successively carry out an observation on their one-day exposure to environment at a rainproof condition for forty days. Simultaneously, by using collecting filters and low-volume Anderson samplers, ionic component concentration and particle size distribution in gaseous and particulate matters in air were measured. Acidic gases are apt to deposit onto alkaline water, and alkaline ones easily deposit onto acidic one. Namely, by approaching residual resistance of these gaseous materials at the solution surface on their deposition to zero, here were investigated a method to classify suspended particulate matters with gaseous ones. By these tests and from a relationship between difference of deposition flux collected onto every alternative surface and concentration of gaseous and particular materials in air, deposition mechanism and rate of the gaseous and particular materials were individually evaluated.
Deposition velocities in daily measurements of SO₂, NH₃ and NO_x were 0.76, 0.70, and 0.04 cm/sec, respectively. It was thought that it was based on low solubility of NO_x to water and larger residual resistance at the water surface than those of other gaseous materials. The deposition velocities in daily measurements of nss-SO₄^2- and NH₄⁺ of fine particles were 0.24 and 0.33cm/sec, respectively, and NO₃^- presenting both particles of fine and coarse size modes were 0.28cm/sec. The deposition velocities on Na⁺, K⁺, and Mg²⁺ of coarse particles were 1.39, 1.18 and 1.32cm/sec, respectively, and the deposition velocity of Ca²⁺ with larger size among the coarse particles was 2.01 cm/sec. As a result, it could be understood that Ca²⁺ particles had a stronger effect of gravitational sedimentation.
It was rare that after depositing on a dry surface, the particulate matters were re-diffused by wind from the dry surface. NO₃^-, NH₄⁺, and Cl^- were observed to evaporate more than 50%, 40%, and 20% after depositing onto the dry surface, respectively. About 80% of SO₄^2- deposited onto water surface was assumed to be affected by deposition of SO₂. And, deposition of SO₂ onto the dry surface was scarcely found.