Atmospheric PAH Deposition: Deposition Velocities and Washout Ratios

Abstract

The urban snowpack effectively acts as a collection device for atmospheric-deposited PAHs. When these PAHs are flushed out in a short time interval along with springtime snowmelt, these cause shockloading to receiving waters. The assessment of PAH deposition, accumulation, and possibly remediation of PAHs in urban snowpacks requires an understanding of source-receptor linkages. In this research, a mechanistic model based on atmospheric dispersion and the physics of wet and dry deposition is described for the transport of PAHs and time-dependent accumulation of PAHs in the snowpack. Two independent data sets of long-term PAH deposition levels from the study area of Sault Ste. Marie, Ontario, Canada have been utilized in this study. The first data set is used to estimate the model parameters (dry deposition velocities and washout ratios) for three PAH species (phenanthrene, fluoranthene, and pyrene) and the second data set for the validation of the model. The dry deposition velocity for all three PAH species is statistically significant, although the washout ratio is not significant in a statistical sense. The statistical conclusions indicate that dry deposition is a dominant deposition process in the urban environment. The point estimates of deposition velocities and washout ratios compare favorably with previous investigations into deposition parameters.