Field Calibration of Rapidly Equilibrating Thin-Film Passive Air Samplers and Their Potential Application for Low-Volume Air Sampling Studies N. J. FARRAR, † T. J. HARNER, ‡ A. J. SWEETMAN, † AND K. C. JONES* ,† Environmental Science Department, Institute of Environmental and Natural Sciences, Lancaster University, Lancaster LA1 4YQ, U.K., and Meteorological Service of Canada, Environment Canada, 4905 Dufferin Street, Toronto, Ontario M3H 5T4, Canada This paper reports on a field calibration and ambient deployment study with rapidly equilibrating thin-film passive air samplers. POlymer-coated Glass (POG) samplers have a coating of ethylene vinyl acetate (EVA) less than 1 μm thick coated on to glass, which can be dissolved off after exposure and prepared for quantification of persistent organic pollutants (POPs) that have partitioned into the film during field exposure. In this study, POGs were exposed for up to18 d, in a study to assess compound uptake rates and their time to approach equilibrium. Results confirmed theoretical predictions, with time to equilibrium varying between a few hours to ca. 20 d for PCB-18 and PCB-138, respectively. Performance reference compounds and contaminated POGs were used to investigate depuration kinetics, confirming that lighter congeners behave extremely dynamically with substantial losses from the films over periods of a few hours. Repeated deployments of the samplers for different 3-d periods yielded detectable levels of a range of PCB congeners, which had partitioned from as little as ∼2 to 10 m 3 air. This highlights the potential utility of POGs for extremely sensitive and dynamic passive air sampling in the future to help improve understanding of sources, environmental fate, and behavior of POPs. Recommendations are made for future improve- ments/refinements in POG sampling and handling procedures. Introduction There is considerable interest at present in developing and utilizing passive air samplers (PAS) for persistent organic pollutants (POPs) in the ambient environment (1-6). PAS provide exciting opportunities to cheaply and efficiently identify sources of POPs and to better understand their environmental distribution, fate, and behavior (7-9). Most of the attention to date has focused on samplers that “integrate” POPs from the atmosphere over time frames of weeks, months, or years. This limits the interpretation of data and excludes processes that affect air concentrations over relatively short time periods (e.g., hours to days). However, a rapidly responding “dynamic sampler”, with a low capacity to store POPs has been developed recently, whichsonce calibrated and better understoodscould fa- cilitate more processed-based studies including source characterization and the determination of gradients/source strengths. This sampler consists of a thin (e.g., <1 μm) film of ethylene vinyl acetate (EVA) coated on a glass cylinder (5). The potential application of this POlymer-coated Glass (POG) sampler was demonstrated by sampling gas-phase PCBs from low volumes of indoor air where the concentrations were quite high (5). The sampler is versatile because it can be operated in the uptake (kinetic) or equilibrium (thermody- namic) sampling mode (1, 10) by varying the thickness of the polymer coating and the exposure time. PAS are cheap, are comparatively easy to deploy, and can be used to sample simultaneously in different locations. Being a thin film, the POG has a low capacity to hold POPs and responds relatively rapidly to changing air concentrations/exposure times. The utility of thin films for assessing air concentrations of POPs has been carried out previously. Although Diamond and co- workers have utilized urban window films as a sampling medium (13), other workers have exploited natural sources of thin film passive samplers by investigating the partitioning of POPs into the thin surface waxes of plant leaves (11, 12). However, the capacity and uptake characteristics of these “thin films” are not controllable, and this can lead to uncertainties in data interpretation, highlighting the need for a reproducible and controllable thin film passive sampler. In other words, the potential advantages of POGs over both these matrixes are that the thickness of the polymer coating can be standardized and uniform between samplers and that the exposure time can be kept consistent. This paper reports on a series of studies designed to improve our understanding of the performance of the POG under field conditions where it can be applied to study the behavior of POPs in the ambient environment. POGs were deployed at a semirural site where POPs have been routinely monitored for many years, alongside conventional active (high-volume) air samplers. More specifically, the objectives were to expand on the information obtained from the simple indoor air deployment study (5) with PCBs to (i) test the feasibility of utilizing POGs to detect short-term changes in ambient air composition; (ii) to clarify the uptake/loss kinetics and time to equilibrium for a range of POPs to POGs deployed under field conditions; and (iii) to investigate the effectiveness of performance reference compounds (PRCs) (14) for cor- recting for differences in uptake rates during different deployment events (15, 16). Principles of POG Sampling The principles behind passive air sampling for POPs have been discussed in some detail elsewhere (1, 17). Essentially, the uptake of SVOCs from the atmosphere into the passive sampler relies upon the absorption of compounds into the polymeric stationary phase; in this case EVA. Such uptake is driven by the ability of the device to constantly re-establish equilibrium between the SVOC concentrations in the at- mosphere to those found in the EVA. Equilibrium partitioning is described by the K EVA-AIR partition coefficient and is controlled by temperature. Other factors known to affect uptake rates and equilibrium include wind speed and the thickness of the stationary phase (EVA); these are discussed in more detail elsewhere (1, 17). * Corresponding author phone: +44-1524-593972; fax: +44-1524- 593985; e-mail: k.c.jones@lancaster.ac.uk. † Lancaster University. ‡ Environment Canada. Environ. Sci. Technol. 2005, 39, 261-267 10.1021/es048904y CCC: $30.25  2005 American Chemical Society VOL. 39, NO. 1, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 261 Published on Web 11/25/2004