Ambient air samples were collected in Chicago, IL between June and October 1995 as part of a study to investigate the dry deposition and air-water exchange of polycyclic aromatic hydrocarbons (PAHs). A modified high-volume sampler (PS-1 sampler) was used to collect airborne PAHs in both the particulate and gas phases. The average total (gas + particulate) Sigma(14)-PAH concentration was 428 +/- 240 ng m(-3), similar to those previously observed in Chicago, IL and other urban areas. The particle/gas phase distribution varied widely. The gas phase percentage ranged from 1.1 to 99.4%, and generally decreased with increasing molecular weight. The amount of PAHs associated with the particulate phase increased with decreasing temperature, probably due to the temperature dependence of gas/particle partitioning. Concentrations of PAHs with molecular weights between 154 and 202 were correlated well with phenanthrene concentrations while compounds with molecular weights higher than 202 had little or no correlation with phenanthrene concentration, probably due to the different partitioning, transport and removal characteristics of low and high molecular weight compounds. (C) 1999 Elsevier Science B.V. All rights reserved.