Organophosphate esters and their transformation products in megacity atmospheres: size-dependent gas-particle partitioning and transformation potential

The size-dependent gas-particle partitioning of transformation products (TPs) from organophosphate esters (OPEs) and the transform potential for OPEs to TPs in ambient atmosphere remain under-investigated. To fill this knowledge gap, we analyzed gaseous and size-fractionated particle samples collected from Beijing, Shanghai, and Guangzhou in China under different meteorological conditions. The concentrations of OPE were comparable to those in other major cities worldwide, but the levels of TPs were lower than those in these cities. The Li-Ma-Yang model predicted well the size-fractionated gas-particle partition coefficients (K_p) of OPEs and TPs with log K_OA > 9.1. Multiple linear regression model incorporating humidity narrowed the gap between predicted and observed K_p of OPEs with log K_OA < 9.1, but still underestimated the K_p values. Hence, humidity-dependent water film adsorption and transformation of these OPEs should be included in future gas-particle partition modeling, especially in fine particles. Size distributions in concentration ratios of nine pairs of OPE to TP were not unified. Temperature exhibited negative effects on gas-particle partitioning of TPs, and inhibited the transformation of tris(2-chloropropyl) phosphate (TCIPP) to bis(1-chloro-2-propyl) phosphate (BCIPP) and triphenyl phosphate (TPhP) to 4-hydroxyphenyl diphenyl phosphate (4-OH-DPhP) in the particulate phase. Gaseous TPs contributed more to the human inhalation health risks of OPEs than particle-bound TPs. These findings are significant for comprehending the fate of atmospheric TPs in urban environment.

Environmental implication

Transformation products (TPs) of organophosphate esters (OPEs) exhibit comparable or even enhanced toxicity relative to OPEs, but their atmospheric behavior remains incompletely understood. In the present study, gaseous and size-fractionated particulate samples were collected in Beijing, Shanghai, and Guangzhou to explore the gas-particle partitioning behavior of TPs and their transformation potential from OPEs. Results indicated that humidity influenced the gas-particle partitioning behavior of compounds with log K_OA < 9.1, especially in fine particles. The transformation potentials of individual OPE and its TP were size-dependent. These findings are significant to comprehending the fates of OPEs and TPs in urban atmosphere.