Exposure risk assessment and synergistic control pathway construction for O3-PM2.5 compound pollution in China

The increasingly pronounced compound pollution issue of fine particulate matter (PM2.5) and surface ozone (O3) concentrations in China has exacerbated the risk of human morbidity and death. In this study, the spatial and temporal characteristics, health risks and synergistic control pathways of PM2.5-O3 compound pollution in 365 cities in China from 2015 to 2020 were investigated based on spatial statistical analysis, integrated risk index model and spatial correlation analysis. The results show that: The strict air pollution control measures lead to a sustained decrease in PM2.5 leading polluted cities and a sustained increase in clean cities during the study period. However, there is a trend of increasing (2015-2017) and then decreasing (2018-2020) in cities with compound PM2.5 and O3 pollution because of changes in volatile organic compounds (VOCs) and NOx caused by human activities. According to the exposure analysis method, the population exposed to PM2.5 dominated polluted cities declined by 471 million from 2015 to 2020; in contrast, the population living in clean cities increased by 460 million. With the intensification of PM2.5-O3 compound pollution in China, the exposure to PM2.5-O3 compound pollution urban population increases sharply from 349 million in 2015 to 622.5 million in 2018, an increase of more than 40 %; as air quality improves after 2017, the population exposed to PM2.5-O3 compound pollution gradually decreases, falling to the equivalent level in 2015 by 2020. Meanwhile, the population health risks attributed to PM2.5 pollution were reduced, whereas the population health risks attributed to PM2.5-O3 compound pollution were aggravated. From a spatial perspective, PM2.5-O3 compound pollution and health risk exacerbation regions were concentrated in northern and eastern China. In addition, we found that PM2.5 and O3 concentrations have significant synergistic trends, which are consistent with the spatial distribution of VOCs and NOx. Therefore, the establishment of a scientific early warning system for PM2.5-O3 compound pollution and the continuous and vigorous promotion of comprehensive emission reduction of NOx and VOCs are conducive to the synergistic management of PM2.5 and O3 in China.