Comprehensively Assessing PM_2.5 Exposure Across Mainland China with Estimated Concentrations Considering Spatial Aggregation

PM_2.5 is a main air pollutant in China. Considering the unevenly distributed PM_2.5 and population in China, an accurate assessment of PM_2.5 exposure is needed. In this study, the population-weighted exposure (PWE) is used to measure the overall PM_2.5 exposure based on 2766 counties across mainland China. The population exposure risk (PER) is used to better assess the partial PM_2.5 exposure risk level for residents at the county level. The PM_2.5 PWE and PER are calculated with the latest 2020 census data and the predicted concentrations estimated by spatial models considering both the geographic similarities and aggregation. The PWE differed from the concentrations across China, especially in four heavily polluted regions and three detected high-concentration clusters. In China, the average PM_2.5 PWE in 2019 was 39.46 μg/m³, 2.41 μg/m³ higher than the mean concentration (37.05 μg/m³). The exposure in three detected clusters was much higher than in the Sichuan Basin (SCB), the Pearl River Delta (PRD), and the Yangtze River Delta (YRD), suggesting the focus of environmental governance should not only be the traditional heavily polluted areas according to administrative divisions. Regions with high concentrations also differed from regions with high PM_2.5 exposure risk. The counties with higher PM_2.5 PER were located in east-central and eastern coastal China, different from the distribution of concentrations. This study clarified the necessity of considering spatial aggregation of PM_2.5 in LUR models and also emphasized the importance of calculating PM_2.5 PWE as exposures in further health effect assessments.