Spatio-Temporal Variability of PM2.5 Concentrations and Their Relationship with Impervious Surface Expansion in the Beijing- Tianjin-Hebei Region, China

The land use/land cover change with rapid urbanization, especially the growth and spread of impervious surface (IS), is changing the structures, degrading the functions of the urban ecological systems, and posing threats to air quality. The IS coverage (ISC) should be recognized as a geographical indicator to reflect the intensity of human development activities. We examine the relationship between urbanization and air pollution in Beijing- Tianjin-Hebei (BTH) region in recent decades, using ISC as a geographical urbanization indicator and PM2.5 as the air pollution index. Our analysis shows that (1) The ISC in the BTH rose from 0.7% to 1.5% from 2000 to 2014. The annual mean of the PM2.5 concentration has soared from 45.7 to $\boldsymbol{77.3 \mu \mathrm{g} / \mathrm{m}^{3} \text {. }}$ With ISC increasing, the PM2.5 pollution tend to exacerbate, and (2) that the hazardous zone (Beijing-Langfang-Tianjin-Tangshan along the highway G1 and Beijing- Baoding-Shijiazhuang-Xingtai-Handan along with the highway G4) were accompanied by the ISC has soared from 1.2% to 2.9%; and (3) that the spatial distribution of PM2.5 aggravation was consistent with the IS expansion in the BTH region, such as the growth of the ISC in the southeast (1.0% to 2.6%) was greater than that in the northwest (0.4% to 0.6%), and the increase of the PM2.5 concentration in the southeast $\boldsymbol{\text { (52.5 to } 98.0 \mu \mathrm{g} / \mathrm{m}^{3})}$ was also greater than that in the northwest $\boldsymbol{\text { (22.7 to } 39.7 \mu \mathrm{g} / \mathrm{m}^{3}).}$ And only Zhangjiakou (1 of 13 cities) satisfies national Target- II $\boldsymbol{(35\ \mu \mathrm{g}/\mathrm{m}^{3})}$ with the lowest ISC of 0.2 %, compared with the highest of 8.0% in Beijing. Finally, at the station level, we found a good fit $(\mathbf{R}=0.803$, P < 0.001) between the ISC of buffer with 3000 m and PM2.5 concentrations.