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

Abstract

A series of emission control measures implemented by the Chinese government have effectively reduced air pollution by 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 (ROSs), 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 ROSs (referred to as G-ROSs and P-ROSs, respectively) in Beijing during the 2015 China Victory Day Parade period when short-term air quality control measures were imposed. 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-ROSs to the atmospheric oxidizing capacity increased, and that of P-ROSs decreased during the CP compared to the NCP. The strict control measures reduced ambient EPFRs, G-ROSs, and P-ROSs by 18.3 %, 24.1 %, and 46.9 %, respectively; these amounts were smaller than the decreases in most other measured pollutants. Although particle-matter-based air quality control measures have performed well in achieving “Parade Blue”, it is difficult to simultaneously reduce the negative impacts of the atmosphere on human health. The Parade Blue days were largely attributed to the dramatic reduction in secondary aerosols, which were also largely responsible for EPFR and ROS reductions. Compared to the cases during the NCP, the source-sector-based concentrations of PM2.5, EPFRs, G-ROSs, and P-ROSs during the CP were reduced by 78.7 %–80.8 % when coming from secondary aerosols, by 59.3 %–65.0 % when coming from dust sources, by 65.3 %–67.0 % when coming from industrial emissions, and by 32.6 %–43.8 % when coming from vehicle emissions, while concentrations from other sources increased by 1.61 %–71.5 %. Vehicle emissions and other sources may play complex roles in air quality and public health. This insight will prompt policymakers to reevaluate current air quality management strategies to more effectively address the challenges posed by pollutants such as EPFRs and ROSs.