A new empirical equation for the gas/particle partitioning of OPFRs in ambient atmosphere.

Gas/particle (G/P) partitioning is a core process governing the atmospheric transport of organophosphate flame retardants (OPFRs). However, accurately predicting the G/P partition performance of OPFRs remains a challenge. In this study, four independent models were employed to estimate the characteristics of OPFR G/P partitioning within the octanol-air partition coefficient range of 4.7 (TMP) to 14.2 (TMPP). The results showed that in the maximum partition domain, the Li-Ma-Yang steady-state model fitted the best, with 85.2% of the predicted G/P partition quotient (log K_P) values within an acceptable deviation range of ±1 log units for OPFRs. Accordingly, no significant deviations were observed between the predicted (0.56 ± 0.32) and monitored (0.52 ± 0.11) values of the average particle-bound fraction (φ_P) for the Li-Ma-Yang model in the maximum partition domain. Large deviations were observed between the monitored values and predicted log K_P values by these four models in the equilibrium domain. Several factors responsible for the significant deviations observed in G/P partitioning values of OPFRs were discussed. These identified factors were used to develop a new empirical equation, which substantially improved log K_P predictions for OPFRs to 75.8% in the equilibrium domain.