Seasonal variation and affecting factors of organophosphate esters in particulate matter in air: a comparison between measured data and model predictions.

Six organophosphate esters (OPEs) with different octanol-air partition coefficient (K) were measured from gas and particle samples collected from an urban area of Central China between June 2018 and May 2019. The highest concentration of total OPEs (∑OPEs) in total suspended particle (TSP) were found in winter, followed by spring, autumn, and summer. ∑OPEs showed significant positive correlation with TSP concentration (p < 0.01), significant negative correlation with temperature (p < 0.01), weak negative linear correlations with relative humility (p < 0.05), and no significant correlations with wind speed (p > 0.05). Although OPEs were not detected in polyurethane foams (PUFs), the poly-parameter linear free energy relationship model (pp-LFER) estimated particle fractions of OPEs (f) were below 2.73% for Tris (2-chloroisopropyl) phosphate (TCIPP), Tris (chloroethyl) phosphate (TCEP), and Tributyl phosphate (TnBP); 67.8% for Triphenyl phosphate (TPhP); and above 99.6% for TBOEP and TCrP. The concentrations of particle-bound TPhP, TCrP, and TBOEP estimated by pp-LFER (C) were 0.19, 0.09, and 0.05 ng/m, which were in good agreement with measurements. However, the estimated C of TCEP, TCIPP, and TnBP showed obvious differences with measured data. According to filter-air partitioning estimated by pp-LFER, the strong adsorption of gaseous OPEs to glass fiber filter (GFF) may be responsible to the underestimation. Besides, the weak adsorption of gaseous OPEs to PUF is likely to be another important reason for the discrepancy between measured and modeled results. Therefore, the risk assessment of gaseous OPEs should be of concern in the further research.