Gas-Particle Partitioning of PCBs and PAHs in the Chicago Urban and Adjacent Coastal Atmosphere:  States of Equilibrium

Abstract

Simultaneous air samples were taken in Chicago and over southern Lake Michigan as part of the AEOLOS Project (Atmospheric Exchange Over Lakes and Oceans). Gas and particle phase concentrations of polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and total suspended particles (TSP) were measured over 12 h periods during July, 1994, and January, 1995. Partitioning of PCBs and PAHs between gas and particle phases was well correlated with the subcooled liquid vapor pressure (p°L) for individual samples, but the relationship differed among samples. For all but a few of the samples the slopes of the log K p vs log p°L lines were statistically greater than -1. Other investigators who have found similar results have concluded that the PCBs/PAHs were not at equilibrium; however, other factors indicate that the PCBs and PAHs in the Chicago/Lake Michigan atmosphere are at equilibrium. Slopes of the regressions of log K p vs log p°L from samples of continental background origin, and therefore assumed to have had sufficient atmospheric residence times to reach equilibrium, are among the shallowest measured (-0.70 to -0.53 and -0.16 to -0.56 for PAHs and PCBs, respectively). One pair of samples where the air mass is believed to have been sampled twice, once in the urban area and again ∼3.4 h downwind, shows no difference in partitioning. PCBs and PAHs measured in Chicago and over Lake Michigan were apparently at equilibrium between the gas and particle phases. A slope of -1 in the regression of log K p vs log p°L is not necessary to describe equilibrium partitioning. Differences in particulate matter may be responsible for the shallow slopes observed.

Polycyclic aromatic hydrocarbons in the atmosphere of Shanghai, China

“…However, many field measurements reported the deviation of m r from −1, and some reasons were proposed (Pankow and Bidleman 1992;Simcik et al 1998). For all the samples in this study, the correlation between log K P and log P o L was checked for each PAH whose concentration was above the detection limit in both phases.…”

Concentrations and gas-particle partitioning of PCDD/Fs in the urban air of Dalian, China

“…However, Goss and Schwarzenbach [11] and Simcik et al [35] argued that a slope value of 1 in the regression of logK p versus logP L 0 is not necessary to describe equilibrium partitioning. Slopes significantly steeper than 1 indicate adsorption while slopes shallower than 0.6 point to absorption, slops in the range between 0.6 and 1 can occur for absorption as well as for adsorption [11].…”

Distribution profile, health risk and elimination of model atmospheric SVOCs associated with a typical municipal garbage compressing station in Guangzhou, South China

“…But it has been argued that a slope of À1 is not necessarily to describe equilibrium partitioning (Simcik et al, 1998). Differences in composition of particle matter may be responsible for the observed slopes deviating from À1.…”