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HAZARDOUS AIR POLLUTANTS: DRY-DEPOSITION PHENOMENA
Citation:
Sehmel, G., R. Lee, AND T. Horst. HAZARDOUS AIR POLLUTANTS: DRY-DEPOSITION PHENOMENA. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/3-84/114.
Description:
Dry-deposition rates were evaluated for two hazardous organic air pollutants, nitrobenzene and perchloroethylene, to determine their potential for removal from the atmosphere to three building material surfaces, cement, tar paper, and vinyl asbestos tile. Dry-deposition experiments were conducted in two stirred chambers. Building materials were placed on the bottom of the stirred chambers, and removal rates were evaluated by introducing the organic air pollutant along with nondepositing sulfur hexafluoride (SF6) tracer gas into a stirred chamber. Changes in airborne concentrations with time were then monitored. Because the HAP removal rates were small, sulfur hexafluoride tracer gas was used to evaluate the rates of leakage from the SC in order to correct the deposition rates. When HAP wall losses were assumed negligible, HAP concentration decreases (corrected using the SF6 leakage rate) ranged from near 0 to 3 %/h. Dry-deposition velocities were calculated from the rate-of-change over time of the airborne concentrations. The calculated deposition velocities were consistently small, approximately .0001 cm/sec or less. These deposition velocities reflect mostly substrate resistance, but the fan speed could not be increased sufficiently to ensure in the limit that only substrate resistance was measured.