Particle Dry Deposition From the Ambient Atmosphere: The Role of Particle-Surface Interactions

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Airborne particles play a vital role in maintaining the earth's energy balance, sustaining ecosystems and influencing global cycles of chemical species. Unfortunately, our understanding of the processes affecting these particles, from emissions to their ultimate fate, is far from complete. A particular deficiency concerns our limited knowledge of particle removal from the atmosphere by dry deposition. The overall goal of this project is to determine the most important factors influencing dry deposition of airborne particles, focusing on interactions between particles and the surface of vegetation. There are three specific objectives: 1) to develop improved mathematical formulations for several mechanisms of particle-surface interaction, 2) to verify these formulations through wind tunnel tests, and 3) to apply the formulations to field conditions by developing and verifying an in-canopy deposition model. Objective 1 will be achieved by improving existing formulations in the areas of turbulent transport through the viscous sublayer, electrostatic attractions, and resuspension. Objective 2 will be achieved by conducting deposition and reentrainment measurements in a wind tunnel using monodisperse uranine particles that can be measured by fluorescence. Finally, objective 3 will be achieved by developing a model that relates airborne concentrations within the canopy and geometry of the vegetation elements are used as model inputs. Measurement of dry deposition of ambient chemical species with known size distributions will allow verification of the model. The results of this study will enable a better understanding of the most important processes influencing particle dry deposition onto natural surfaces. This, in turn, will yield more accurate prediction of dry deposition as a component of atmospheric transport models.