On the dry deposition of submicron particles

A review of past micrometeorological studies on the dry deposition of submicron particles in the atmospheric surface layer indicates that various studies have produced widely varying estimates of the dry deposition velocities. Eddy correlation measurements in the 1980s showed that the deposition velocity for submicron sulfate to short vegetation were much larger during the daytime and varied more strongly with atmospheric stability than had been predicted on the basis of theoretical and wind tunnel studies. Micrometeorological measurements above forests in the 1990s confirmed a strong stability dependence for deposition of submicron particles and yielded even larger deposition velocities for sulfate and nitrates than seen in the 1980s; variations associated with friction velocity, surface wetness, and relative humidity were parameterized. Results from several experiments remain difficult to interpret when the fluxes of particles were made without regard to chemical composition. The observed particle deposition varied greatly for different types of surfaces, ambient conditions, and particle size range. Potential confounding processes include the effects of vertical gradients in relative humidity near the surface in changing size distributions, suspension of fine particulate material from dry surfaces, and gas-to-particle conversion in forest canopies. Future observations of particulate flux should include measurement according to both size and chemical species of particles.