Persistently high oxidative burden of PM_2.5 amidst declining mass concentration: Evidence from long-term observation...

Albeit the declining concentration of PM_2.5, health benefits of air pollution mitigation in China remain limitedly evaluated. Oxidation potential (OP) is the capacity of PM_2.5 to generate reactive oxygen species (ROS), served as an indicator for PM-induced adverse health effects. Here, acellular (DTT) and cellular OP (in vitro ROS) as well as detailed composition were characterized for PM_2.5 collected in Shanghai (2018-2022). Although PM_2.5 significantly decreased, the inhalation associated oxidative burden (OP_v) remains mostly unchanged due to the enhanced intrinsic OP_m in Shanghai. DTT_v and ROS_v correlated positively with PM_2.5 and O_x (O₃ + NO₂), exhibiting high sensitivity towards source indicating components (i.e., levoglucosan, transition metals, polycyclic aromatic hydrocarbons (PAHs), and secondary organic aerosol (SOA)) in SHAP (SHapley Additive exPlanations) analysis. As illustrated by positive matrix factorization (PMF) integrating with multiple linear regression (MLR), the major contributors to OP_v across different years in Shanghai were biomass burning and traffic (48% for DTT_v and 59% for ROS_v). Further backward trajectory analysis showed that SOA related air mass has become increasingly important for OP_v in recent years (26% of DTT_v and 35% of ROS_v in 2018 compared to 53% of DTT_v and 49% of ROS_v in 2022). Results from this study indicate the significance of mitigating secondary pollution for future air quality regulation from a public health perspective.