Spatial characteristics of the PM2.5/PM10 ratio and its indicative significance regarding air pollution in Hebei Province, China

Particulate matter (PM) is the primary air pollutant in northern China. The PM2.5/PM10 ratio has been used increasingly as an indicator to reflect anthropogenic PM pollution, but its advantages compared with individual PM2.5 or PM10 concentrations have not been proven sufficiently by experimental data. By dividing Hebei Province (China) into seven natural ecological regions, this study investigated the spatial characteristics of the PM2.5/PM10 ratio and its relationships with PM2.5, PM10, economic density, and wind speed. Results showed that the PM2.5/PM10 ratio decreased from east to west and from south to north, with an annual average value in 2019 of 0.439-0.559. The characteristics of the spatial variation of the PM2.5/PM10 ratio were different to those of either PM2.5 or PM10 concentration, indicating that PM pollution reflected by the PM2.5/PM10 ratio is not entirely consistent with that by PM2.5 and PM10 concentrations. In comparison with PM2.5 or PM10 concentration, the PM2.5/PM10 ratio had higher (lower) correlation with economic density (wind speed), indicating that the PM2.5/PM10 ratio is a better indicator used to reflect the intensity of anthropogenic emissions of PM pollutants. According to the characteristics of the spatial variations of the PM2.5/PM10 ratio and the PM2.5 and PM10 concentrations, the seven ecological regions of Hebei Province were categorized into four different types of atmospheric PM pollution: "three low regions," "three high regions," "one high and two low regions," and "one low and two high regions." This reflects the comprehensive effect of the intensity of anthropogenic PM emissions and the atmospheric diffusion conditions.