Atmospheric Washout of Polycyclic Aromatic Hydrocarbons in the Southern Chesapeake Bay Region

Abstract

Vapor washout of selected polycyclic aromatic hydrocarbons (PAHs), determined from discrete atmospheric and integrated precipitation samples collected every two weeks throughout 1991, was observed to be controlled by the Henry's law constant for the compound at the temperature of deposition (5-29 °C). Particle washout was found to be relatively constant for the various PAHs but to vary seasonally, with higher particle scavenging occurring in the spring and summer compared to the fall/winter. Vapor washout coefficients were negatively correlated with rainfall intensity, with stronger dependencies on precipitation rate for high molecular weight PAHs relative to low molecular weight, volatile compounds. This observation indicates that gases of the less volatile PAHs may not achieve equilibrium between air and raindrops during extremely intense precipitation events. Particle washout coefficients for PAHs were positively correlated with rainfall intensity, indicating an increased efficiency for particle scavenging from the atmosphere with precipitation rate.