Sources and temporal trends of chlorinated paraffins in PM_2.5 in a megacity in central China

The widespread use of chlorinated paraffins (CPs) poses significant ecological and health risks. However, existing studies on CPs are generally short, and studies on their regional sources are limited. Herein, we continuously monitored the concentrations of short-chain CPs (SCCPs) and medium-chain CPs (MCCPs) in PM_2.5 in a megacity near industrial areas to investigate their sources, seasonal and annual variations, and potential health risks. In PM_2.5, the concentration of SCCPs (22.6 ± 15 ng m^-3) was significantly higher than that of MCCPs (13.2 ± 10.3 ng m^-3). The dominant congeners were C₁₁Cl_8-9 for SCCPs and C_14-15Cl_7-9 for MCCPs. A clear seasonal variation was observed, with the highest CP concentrations in winter (39.8 ± 23.8 ng m^-3) and the lowest in summer (23.3 ± 7.25 ng m^-3). Moreover, SCCP concentrations in PM_2.5 showed a decreasing trend following the implementation of restrictions under the Stockholm Convention in 2017, while MCCP concentrations exhibited no obvious trend. Back-trajectory analysis indicated that atmospheric CP concentrations were strongly influenced by localized sources and meteorological conditions (such as wind speed). The main regional sources of CPs were airflows from the northwest and northeast, which passed through areas with a high density of CP production facilities and accounted for 87.6 % of the total air mass. Although CPs did not pose an immediate threat to human health, their long-term effects warranted attention, especially for vulnerable populations such as children. The CP exposure risk for children (<18 years) was four times greater than that for the elderly (>80 years). This study highlights the long-term trends and regional sources of CPs, providing policymakers with insights for developing effective CP reduction strategies.