Field Calibration and PAS-SIM Model Evaluation of the XAD-Based Passive Air Sampler for Semi-Volatile Organic Compounds

Abstract

The use of passive air samplers (PAS) for semi-volatile organic compounds (SVOCs) continues to expand. To advance quantitative understanding of uptake kinetics, we calibrated the XAD-PAS, using a styrene–divinylbenzene sorbent, through a year-long side-by-side deployment with an active sampler. Twelve XAD-PASs, deployed in June 2020, were retrieved at 4-week intervals, while gas phase SVOCs were quantified in 48 consecutive week-long active samples taken from June 2020 to May 2021. Consistent with XAD’s high uptake capacity, even relatively volatile SVOCs, such as hexachlorobutadiene, displayed linear uptake throughout the entire deployment. Sampling rates (SRs) range between 0.1 and 0.6 m3 day–1 for 26 SVOCs, including brominated flame retardants, organophosphate esters, and halogenated methoxylated benzenes. SRs are compared with experimental SRs reported previously. The ability of the existing mechanistic uptake model PAS-SIM to reproduce the observed uptake and SRs was evaluated. Agreement between simulated and measured uptake curves was reasonable but varied with compound volatility and the assumed stagnant air layer boundary thickness. Even though PAS-SIM succeeds in predicting the SR range for the studied SVOCs, it fails to capture the volatility dependence of the SR by underestimating the length of the linear uptake period and by failing to consider the kinetics of sorption.

Unbiased Passive Sampling of All Polychlorinated Biphenyls Congeners from Air

“…The new SRs are generally lower than the previously reported ones. 47 The SRs derived for various SVOCs in the same calibration experiment 41 were also lower than previously reported ones. SRs in the XAD-PAS are expected to increase slightly with increasing ambient temperature and wind speed.…”

“…We earlier reported a similar correlation between SR and log K XAD/air for 26 SVOCs. 41 However, the linearity of the regression is more pronounced here, potentially due to the consistent molecular structures and, therefore, properties of the PCBs. The SR for PCB-63 (0.57 m 3 •day −1 ) is higher than that of the other 65 congeners and therefore deviates from the linear regression (Figure 1).…”

“…Here, we present the results of the analysis for the PCBs in a calibration study that has been described previously. 41 As the earlier publication 41 contains experimental details, including field sampling, sample treatment, quality assurance and control, we only provide a summary here. Forty-eight consecutive weeklong active air samples were taken using a midvolume AAS (MV-AAS, ∼500 m 3 sample −1 ) in a eastern suburb of Toronto from June 17, 2020, to May 19, 2021.…”

“…13 Because the XAD-PAS has been shown repeatedly to not sample particle-bound substances above detection limits, GFFs were not analyzed; only PCBs nominally in the gas phase, i.e., quantified in the PUF-XAD−PUF sorbent, were used in the calculation of sampling rates. 41 Calculation of Sampling Rates (SR). During the linear uptake phase, the SR of a PCB in the XAD-PAS is linearly related to the effective sampling volume V eff (m 3 ):…”

“…Here, we present the results of the analysis for the PCBs in a calibration study that has been described previously . As the earlier publication contains experimental details, including field sampling, sample treatment, quality assurance and control, we only provide a summary here.…”