Item talk:Q147586

PAH volatilization following application of coal-tar-based pavement sealant

Coal-tar-based pavement sealants, a major source of PAHs to urban water bodies, have recently been identified as a source of volatile PAHs to the atmosphere. We tracked the volatilization of PAHs for 1 year after application of a coal-tar-based pavement sealant by measuring gas-phase PAH concentrations above the pavement surface and solid-phase PAH concentrations in sealant scraped from the surface. Gas-phase concentrations at two heights (0.03 and 1.28 m) and wind speed were used to estimate volatilization flux. The sum of the concentrations of eight frequently detected PAHs (ΣPAH₈) in the 0.03-m sample 1.6 h after application (297,000 ng m^-3) was about 5000 times greater than that previously reported for the same height above unsealed parking lots (66 ng m^-3). Flux at 1.6 h after application was estimated at 45,000 μg m^-2 h^-1 and decreased rapidly during the 45 days after application to 160 μg m^-2 h^-1. Loss of PAHs from the adhered sealant also was rapid, with about a 50% decrease in solid-phase ΣPAH₈ concentration over the 45 days after application. There was general agreement, given the uncertainties, in the estimated mass of ΣPAH₈ lost to the atmosphere on the basis of air sampling (2–3 g m^-2) and adhered sealant sampling (6 g m^-2) during the first 16 days after application, translating to a loss to the atmosphere of one-quarter to one-half of the PAHs in the sealcoat product. Combining the estimated mass of ΣPAH₈ released to the atmosphere with a national-use estimate of coal-tar-based sealant suggests that PAH emissions from new coal-tar-based sealcoat applications each year (~1000 Mg) are larger than annual vehicle emissions of PAHs for the United States.