PM2.5-bound organophosphate flame retardants (OPFRs) and the transformation products in Hong Kong and Beijing: Spatio-temporal variations on their sources, transformation, and source-specific health risks

Organophosphate flame retardants (OPFRs), an emerging class of organic pollutants, are commonly detected in atmospheric fine particulate matter (PM2.5) and pose potential risks to human health. This study aims to systematically investigate atmospheric OPFRs in Beijing and Hong Kong through advanced chromatography-mass spectrometry techniques, combined with field monitoring, laboratory simulations, source apportionment, and cell-based toxicological experiments. Specifically, the project seeks to: (1) identify and quantify traditional and novel OPFRs, along with their atmospheric transformation products, in PM2.5 samples collected from both cities over a three-year campaign, while mapping their spatiotemporal distribution; (2) characterize the atmospheric transformation products of OPFRs, particularly novel ones, via laboratory simulation experiments; (3) apply a tracer-integrated source apportionment model to quantitatively assess the contributions of primary emissions and secondary formations to OPFRs; and (4) perform cell-based toxicological experiments to examine how atmospheric transformations affect OPFR toxicity and evaluate the roles of various sources and processes in driving these risks. By focusing on the characterization of OPFRs and their transformation products in these two megacities, this research provides a comprehensive framework for evaluating emerging atmospheric organic pollutants from their sources to associated health risks. Ultimately, the findings will offer a scientific foundation for regional OPFR pollution control strategies, with important implications for protecting public health.