| Abstract
| - In the second of two papers documenting theimportance of submicron particles in controlling theconcentrations and distributions of organic contaminants in precipitation, we examine the percipitationscavenging of polycyclic aromatic hydrocarbons(PAHs) as a function of the size distribution ofatmospheric particles. We argue that particle scavenging rather than gas scavenging is the dominantremoval mechanism for PAHs from the atmosphereby precipitation and that previously reported PAHgas scavenging ratios were overestimated due to thepresence of submicron particles in the operationallydefined dissolved phase of precipitation samples. Ina series of five storms in the Chesapeake Bay regionduring summer 1992, dimensionless PAH scavengingratios for submicron particles range from 104 to105,while those for larger particles (>0.5 μm) range from105 to 106. In contrast, gas scavengingratios, aspredicted from temperature-corrected Henry's lawconstants, range from 10 to 500. The particlescavengingratios of PAHs associated with large and smallparticles are similar to those measured for a varietyof inorganic species and with those predicted for in-cloud scavenging of trace atmospheric species.Relativestandard deviations of PAH particle scavengingratios measured during the five storms are nearly 100%,suggesting that precipitation scavenging mechanismsare highly variable among the storms. Thisvariability should be considered when using gas andparticle scavenging ratios to model wet depositionalfluxes of organic contaminants from theatmosphere.
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