Slopes and intercepts from log-log correlations of gas/particle quotient and octanol-air partition coefficient (vapor-pressure) for semi-volatile organic compounds: I. Theoretical analysis.

Yi-Fan Li, Li-Na Qiao, Robie W Macdonald

Chemosphere 2021 Jun

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Gas/particle partitioning governs the transport and fate of semi-volatile organic compounds (SVOCs) released to the atmosphere. The partition quotient of SVOCs, KP, is related to their subcooled liquid vapor pressure (logKP = mp logPL + bp) and to their octanol-air partition coefficient (logKP = mo logKOA + bo). Previous theory predicts that -mp and mo should be close to, or equal to 1 based on the assumption that gas- and particle-phases are at equilibrium in the atmosphere. Here, we develop analytical equations to calculate mo and bo as functions of logKOA and mp and bp as functions of logPL. We find that experimental, analytical, or statistical artifacts and other reported factors are not the leading causes for deviations of the slopes, mp and mo, from -1 and 1, respectively. Rather, it is the inherent parameter, KOA, that determines mo and bo, and equivalently, PL is the major parameter determining mp and bp, and such deviations are evidence that equilibrium is an inappropriate assumption. In contrast, the actual steady-state between gas and particle phases of SVOCs leads that their -mp and mo should range from 0 to 1, implying that equilibrium is a reasonable assumption only when -mp and mo are larger than 0.49. To illustrate these points, we provide a detailed discussion of the global atmospheric transport of polybrominated diphenyl ethers (PBDEs) with emphasis on Polar Regions where low air temperatures favor a special steady-state, where their slopes mp and mo can reach 0, indicating a constant value of logKP (-1.53). Copyright © 2020 Elsevier Ltd. All rights reserved.

Citation

Yi-Fan Li, Li-Na Qiao, Robie W Macdonald. Slopes and intercepts from log-log correlations of gas/particle quotient and octanol-air partition coefficient (vapor-pressure) for semi-volatile organic compounds: I. Theoretical analysis. Chemosphere. 2021 Jun;273:128865