AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Investigation of Ultrafine Particle Deposition onto Vegetation Branches in a Wind Tunnel
MING-YENG LIN, Gabriel Katul, Andrey Khlystov, Research Triangle Institute
Abstract Number: 537 Working Group: Urban Aerosols
Abstract The deposition of UFP onto vegetated surfaces remains a major challenge to be confronted because of the multiplicity of approaches that account for the presence of vegetation. On the one hand, some approaches represent the vegetation as fibrous filters with a preferential size, while other conventional approaches represent the vegetation as a random porous medium. Using wind tunnel studies, the collection efficiency of UFP by pine and juniper at five different wind speeds, two branch orientations, and two packing densities was measured and analyzed using these two representations for the canopy. The experiments agreed well with predictions from filtration theory when the derived effective fiber diameters for pine and juniper are 0.054 (±0.001) cm and 0.065 (±0.001) cm, respectively, with the values in parentheses representing 95% confidence intervals. Moreover, it was found that the near-linear pressure drop across the vegetation can provide a first order estimate of the UFP collection efficiency, in agreement with the filtration theory. The predictions from porous media representations of the vegetation-air system also agreed well with the wind-tunnel measurements here. Upon bridging these two approaches, estimates of the effective fiber diameter can now be derived from conventional canopy attributes, such as the leaf area index. These results provide an alternative way for atmospheric models to characterize the properties of vegetation for UFP deposition calculations.