A conceptual framework for the thermodynamic displacement of semi-volatile organic compounds by extractable organic matter in polyurethane foam passive air samplers: A potential hypothesized source of underestimation in global monitoring

Abstract

Polyurethane foam-based passive air samplers (PUF-PAS) are central to global monitoring networks, including the Global Atmospheric Passive Sampling (GAPS) network and the European Monitoring and Evaluation Programme (EMEP), for the determination of persistent organic pollutants (POPs). Current data models are largely predicted on the assumption of infinite capacity, treating the PUF-air partition coefficient (K_PUF-air) as a thermodynamic constant. However, field observations in high-aerosol environments, where high concentrations of aerosols are prevalent, indicate that the PUF matrix accumulates a significant mass of non-target extractable organic matter (EOM). This study hypothesizes that EOM loading acts as a co-solute that modulates the activity coefficients of target semi-volatile organic compounds (SVOCs), thereby inducing a thermodynamic shift that suppresses the effective K_PUF-air. The resulting matrix-induced suppression is hypothesized to lead to the premature termination of the linear uptake phase and a theoretically simulated bias in effective air volumes (V_air). While direct experimental verification is required, the present preliminary sensitivity analysis suggests a potential model-based underestimation of atmospheric concentrations by 20-50% in heavily contaminated environments under assumed conditions. This study proposes a conceptual capacity-correction framework to account for EOM-induced bias and suggests the strategic evaluation of sorbent-impregnated PUF (SIP-PAS) to maintain data integrity in heavily contaminated environments.