Measurement report: Impact of emission control measures on environmental persistent free radicals and reactive oxygen species – A short-term case study in Beijing

A series of emission control measures implemented by the Chinese government have effectively reduced air pollution of multiple pollutants in many regions of the country in recent decades. However, the impacts of these control measures on environmental persistent free radicals (EPFRs) and reactive oxygen species (ROS), the two groups of chemical species that are known to be linked with adverse human health effects, are still not clear. In this study, we investigated the levels, patterns, and sources of EPFRs and gas- and particle-phase ROS (referred to as G-ROS and P-ROS, respectively) in Beijing during the 2015 China Victory Day Parade period when short-term air quality control measures were imposed. The strict control measures reduced ambient EPFRs, G-ROS, and P-ROS by 18.3 %, 24.1 %, and 46.9 %, respectively. EPFRs in the non-control period (NCP) tended to be radicals centered on a mixture of carbon and oxygen, while those in the control period (CP) were mainly oxygen-centered free radicals. The contribution of G-ROS to the atmospheric oxidizing capacity increased and/or that of P-ROS decreased during CP compared to NCP. The “Parade Blue” days were largely attributed to the dramatic reduction in secondary aerosols, which were also largely responsible for EPFRs and ROS reductions. Our findings demonstrate how effective control measures are in reducing EPFRs and ROS and provide insights into the correlations, sources, and formation processes of EPFRs and ROS.