Abstract View
Using Rain Washoff to Estimate Dry Deposition of Atmospheric Aerosols to Horizontal Urban Surfaces
ALEXANDER JOHNSON, Cliff Davidson, Syracuse University
Abstract Number: 331
Working Group: Urban Aerosols
Abstract
Building roofs comprise a major fraction of the overall horizontal urban surface area and are receptors of dry deposited aerosols. During a storm, rainwater will wash the dry deposited material from a building roof into stormwater runoff. Measuring the concentrations of certain chemical species in runoff from a building roof and the amount of runoff could therefore be used to estimate dry deposition to that surface during the antecedent dry period.
The goals of this study were to measure dry deposition to horizontal urban surfaces and to measure rain washoff of dry deposited material from the surfaces. In each experiment, two flat Teflon coated disks and two bowl-shaped disks of similar size were exposed to the atmosphere on the roof of Hinds Hall at Syracuse University to collect dry deposition. Airborne concentrations were simultaneously measured. Shortly before a rainstorm, samples were collected from the flat disks. In the subsequent storm, fresh rain and runoff from the bowl-shaped disks were collected. All samples were analyzed to determine the dry deposition fluxes and dry deposition velocities of fluoride, chloride, nitrate, sulfate, ammonium, sodium, magnesium, potassium, and calcium to the disks.
Dry deposition fluxes measured to the flat disks and to the bowl-shaped disks show reasonable agreement, suggesting the reliability of using the bowl-shaped disks to assess rain washoff. Nearly complete washoff of the dry deposited material from the bowl-shaped disks is possible under a steady rain.
Additional experiments are underway to measure dry deposition to a green roof by washing the leaves of vegetation after lengthy dry periods. In future experiments, concentrations of chemical species in rain runoff from building roofs and from vegetation will be used to estimate dry deposition of these species in urban areas.