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

The logarithm of gas/particle (G/P) partition quotient (logK(P)) has been found to have a linear relationship with logK(OA) (octanol-air partition coefficient) with slope m(o) and intercept b(o) and logP(L) (subcooled liquid vapor pressure) with slope m(p) and intercept b(p). In the sister paper of the present work, analytical equations to predict the slope m(o) and intercept b(o) based on logK(OA) and predict the slope m(p) and intercept b(p) based on logP(L) are developed using steady state theory. In this work, the equations are evaluated using world-wide monitoring data (262 pairs for m(o) and b(o) values and 292 pairs for mp and b(p) values produced from more than 10,000 monitiring data worldwide) for selected seven groups of semi-volatile organic compounds (SVOCs), including polybrominated diphenyl ethers (PBDEs), polychlorinated dibenzo-p-dioxins and polychorinated dibenzofurans (PCDD/Fs), polyclorinated biphenyl (PCBs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated naphthalenes (PCNs), organochlorinated pesticides (OCPs), novel brominated flame retardants (NBFRs), and other selected halogenated flame retardants. The slopes and intercepts predicted by the steady state equations reproduce the trends observed in monitoring regression results for the seven SVOC groups, with 44.4% of the variation of monitoring m(o) values accounted for by logK(OA) and 48.2% of the variation of monitoring m(p) values accounted for by logP(L). Theoretically, the values of m(o) can be any value between 0 and 1 dependent on the values of K-OA, and are not constrained to 1 as in equilibrium theory. Likewise, the values of m(p) can be any value between 0 and -1 dependent on the values of P-L, and not constrained to -1 predicted by the equilibrium theory. The influence of sampling artifacts on the G/P partitioning of SVOCs has most likely been overemphasized by the equilibrium theory. Thus, the equilibrium approach should be abandoned in favor of the steady state approach for calculating the G/P partition quotients for SVOCs with high K-OA values (>10(11.38)) or low P-L values (<10(-4.92)). (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

This study found a linear relationship between gas/particle partition coefficients and octanol-air partition coefficients as well as subcooled liquid vapor pressures. Analytical equations based on steady state theory were developed to predict related parameters, and the evaluation using global monitoring data showed that the equations could accurately reproduce the observed trends in monitoring results.