The Promotion Effect of Dust on Oxidative Potential of PM_2.5 via Photochemical Aging

The health risks of atmospheric particulate matter (PM) are closely linked to its diurnal variation because of the circadian rhythm of human activity. However, the diurnal variability of the oxidative potential (OP) of PM_2.5 (OP_PM2.5), which is a key toxicity indicator of PM_2.5, and its driving factors remain poorly understood. This study investigated the diurnal patterns and drivers of OP_PM2.5 based on both field measurements in Beijing in 2023 and laboratory experiments. The daytime OP_PM2.5 was moderately higher (1.2 times) than nighttime levels. While nighttime OP_PM2.5 primarily depended on carbonaceous aerosols from vehicles and biomass combustion, the enhanced daytime OP_PM2.5 was ascribed to the additional contributions from transition metals, dust, and secondary aerosols. OP_PM2.5 on sandstorm days increased by up to 46% after 0.5 h of photochemical aging, due to synergistic interactions between dust and vehicle/biomass combustion aerosols, forming reactive oxygen species (ROS)-facilitating functional groups including aromatic carbonyls and peroxides. In particular, Fe₂O₃ in dust may catalyze ROS formation under irradiation. However, extended aging (>4 h) reduced OP_PM2.5 through photochemical bleaching. These results provide new insights into the health impacts of PM and inform health-oriented air quality control strategies through the coordinated reduction of dust, vehicle, and biomass combustion emissions.