| Summary: | The urban form (e.g., city size, shape, scale, density, etc.) can impact the air quality and public health. However, few studies have been conducted to assess the relationship between the urban form and PM<sub>2.5</sub> concentrations on a regional scale and long-term basis in China. In this study, we explored the impact of the urban form on the PM<sub>2.5</sub> concentrations in four different regions (i.e., northeast, central, east, western) across China for the years 2000, 2005, 2010, and 2015. Five landscape metrics were classified into three characteristics of the urban form (compactness, shape complexity, and urban expansion) using high-resolution remote-sensing data. With considerations given to regional differences, panel-data models and city-level panel data were used to calculate the impact of the urban form on the PM<sub>2.5</sub> concentrations. The results of the study indicate that urban expansion is positively correlated with the PM<sub>2.5</sub> concentrations across China, with the only exception being the country’s western region, which suggests that urban extension is conducive to increasing the PM<sub>2.5</sub> levels in relatively developed regions. Meanwhile, the positive relationship between the irregularity of cities and the PM<sub>2.5</sub> concentrations indicates that reducing the urban shape complexity will help to mitigate PM<sub>2.5</sub> pollution. Moreover, urban compactness, which mainly refers to the landscape-division-index values, proved to have a negative effect on the PM<sub>2.5</sub> concentrations, suggesting that the optimization of urban spatial compactness could reduce PM<sub>2.5</sub> levels. The findings of this study are beneficial for a better understanding of the intensity and direction of the effect of the urban form on PM<sub>2.5</sub> concentrations.
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