10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
The Effect of Vegetation on the Deposition and Dispersion of Ultrafine Particles Carrying Different Charges
MING-YENG LIN, Gabriel Katul, Andrey Khlystov, Chia-Ren Chu, National Cheng Kung University
Abstract Number: 791 Working Group: Aerosol Transport and Transformation
Abstract Ultrafine particles (UFP) continue to receive increased attention due to their dual role in cloud microphysics and human health. Charged UFP can contribute a significant fraction of total UFP concentration, yet their deposition onto vegetation remains a subject of inquiry. Given the areal coverage of vegetation over land, vegetation is commonly assumed to be a large sink for UFP. Despite its broad significance, previous laboratory studies mainly focused on neutral UFP deposition onto canopies. Here, wind tunnel experiments are used to investigate the effect of vegetation on the deposition and dispersion of UFP carrying different charges.
To characterize the effect of vegetation on the deposition of UFP (size range 12.6 – 102 nm) carrying different charge, a small wind tunnel was first used. Juniper branches (Juniperus chinesis) covered the entire working section of this wind tunnel (i.e., the air flow is only through vegetation) and particle collection was determined from concentration differences across the vegetation section. Three different wind speeds were used (0.3, 0.6, and 0.9 m/s) in the experiments and their results were interpreted using single fiber theory. Results indicate that single fiber theory can be used to represent deposition of singly-charged UFP onto vegetation if both the image force and Brownian diffusion are simultaneously considered.
To investigate the effect of roadway vegetation on the dispersion of UFP carrying different charge, a boundary layer wind tunnel was used in this experiment. A line source simulating traffic emission was constructed and different row of trees (zero, one, and two rows) were used to explore the effect ‘vegetation barriers’ on UFP dispersion. A Tandem Differential Mobility Analyzer (TDMA) system was employed to examine the dispersion of UFP carrying different charges downwind of the roadway vegetation. Three different wind speeds (1, 2, and 3 m/s) were also tested. Preliminary results indicate that charged UFP number concentration decreases downwind of the vegetation as expected, the decay rate of charged UFP is faster than neutral UFP. The study results provide guidance for future climate and air quality models incorporating UFP.