Investigation of the spatially varying relationships of PM with meteorology, topography, and emissions over China in 2015 by using modified geographically weighted regression.

PM pollution is caused by multiple factors and determining how these factors affect PM pollution is important for haze control. In this study, we modified the geographically weighted regression (GWR) model and investigated the relationships between PM and its influencing factors. Experiments covering 368 cities and 9 urban agglomerations were conducted in China in 2015 and more than 20 factors were considered. The modified GWR coefficients (MGCs) were calculated for six variables, including two emission factors (SO and NO concentrations), two meteorological factors (relative humidity and lifted index), and two topographical factors (woodland percentage and elevation). Then the spatial distribution of MGCs was analyzed at city, cluster, and region scales. Results showed that the relationships between PM and the different factors varied with location. SO emission positively affected PM, and the impact was the strongest in the Beijing-Tianjin-Hebei (BTH) region. The impact of NO was generally smaller than that of SO and could be important in coastal areas. The impact of meteorological factors on PM was complicated in terms of spatial variations, with relative humidity and lifted index exerting a strong positive impact on PM in Pearl River Delta and Central China, respectively. Woodland percentage mainly influenced PM in regions of or near deserts, and elevation was important in BTH and Sichuan. The findings of this study can improve our understanding of haze formation and provide useful information for policy-making.