Particulate Dry Deposition and Overall Deposition Velocities of Polycyclic Aromatic Hydrocarbons

Previous studies have shown that the dry deposition of semivolatile organic compounds to the Great Lakes can account for a significant fraction of their total inputs. However, there is no generally accepted method to directly measure dry deposition. In this study the particulate dry deposition of polycyclic aromatic hydrocarbons (PAHs) was measured using smooth surrogate surfaces during the winter of 1996–1997 in Chicago. Concurrently, ambient air samples were collected. Average particulate ${\Sigma }_{13}-\mathrm{PAH}$ fluxes and ambient concentrations were $120\pm 28\mu g/m^{2}d$ and $30\pm 16\mathrm{ng}/m^3\text{,}$ respectively. The measured particulate dry deposition fluxes were similar to those measured in other urban areas. Overall dry deposition velocities of PAHs calculated using the dry deposition fluxes and ambient concentrations averaged $4.5\pm 3.1\mathrm{cm}/s\text{.}$ This value is higher than values typically used to estimate PAH particulate deposition, however, it agrees well with values determined using similar techniques. The overall dry deposition velocity for individual PAHs generally decreased with increasing molecular weight. This finding is consistent with the previous experimental studies that have shown that a greater fraction of the higher molecular weight PAHs are associated with fine particles relative to the lower molecular weight compounds.