Satellite-Based Spatiotemporal Trends and Transport Analysis of PM2.5 in Hubei, Central China

As particulate matter with an aerodynamic diameter less than 2.5 μm (PM_2.5) has been widely proven to be linked with varieties of adverse health effects, many studies conducted PM_2.5 estimations on large scale based on satellite-derived aerosol optical depth, combined with meteorological information as auxiliary data. As one of the economic, politic and cultural centers in central China, Hubei province suffered from severe fine particle pollution in recent years, however, few systematic studies revealing the spatiotemporal characteristics and transport rules of PM_2.5 have been conducted in Hubei. In this study, the nested linear mixed effects model was respectively employed in each city of Hubei province to estimate PM_2.5 concentrations, due to the complex topographical conditions in Hubei. The model validation results showed that the highest R² values reached up to 0.9, and the lowest R² values yielded 0.75. The overall PM_2.5 estimation maps demonstrated that northwestern and southeastern Hubei were relatively clean regions, while the cities in southern and eastern Hubei experienced severe PM_2.5 pollutions. These PM_2.5 patterns could be caused by the combined effects of spatiotemporal variations of emissions and air mass transport and dispersion. The annual averaged PM_2.5 estimations declined year by year in most cities, which was consistent with previous studies based on ground atmospheric monitors, indicating that the relevant emissions controlling policies in Hubei came into effect in recent years. In addition to that, the potential wind corridors in each cities of Hubei have been analyzed via the significance of wind direction in each PM_2.5 estimation model, which illustrated three transport corridors and one circulation plain in Hubei, namely the north-south Jin-Jing corridor in the middle of Hubei, the east-west Suizhou corridor in northern Hubei, the east-west Huangshi corridor in southeastern Hubei, and lake areas located on the Jianghan Plain. Furthermore, these corridors and plain have been evaluated by the near surface atmospheric circulation theory and the HYSPLIT model, which proved the effectiveness of regional transport rules in Hubei. In summary, this study not only offered a reliable method to analyze regional PM_2.5 transport but also provided guidance on air quality management in Hubei.