Urban compactness and patch complexity influence PM2.5 concentrations in contrasting ways: Evidence from the Guangdong-Hong Kong-Macao Greater Bay Area of China

[Display omitted] •Patch complexity and urban compactness indexes were developed to assess urban form.•The impact of urban form on PM2.5 was explored in GBA by spatial panel models.•The complexity of urban patches had a negative effect on PM2.5 concentrations.•The impact of urban compactness on PM2.5 concentrations was positive.•A more complex and less compact urban form was adoptable in terms of reducing PM2.5. Given the serious threat of PM2.5 pollution to the environment and public health in China, reducing PM2.5 concentrations through urban planning practices has become a common interest of urban planners and policymakers. In this regard, identifying the relationship between urban form and PM2.5 concentrations has been a matter of much concern. This paper seeks to investigate how urban form influences PM2.5 concentrations by taking the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) as a case study. First, the urban form was assessed by two indicators, i.e., the patch complexity index (PCI) and urban compactness index (UCI), which were developed based on multiple landscape metrics and the principal component analysis. Then, the relationship between PM2.5 concentrations and the two urban form indicators was revealed by spatial panel models. Our results mainly showed that PCI and UCI were negatively and positively associated with PM2.5 concentrations, respectively, indicating that less compact urban forms with high patch complexity had advantages in reducing the PM2.5 concentrations. According to these empirical results, the mixed-use urban development with high green coverage, which is conducive to constructing a more complex and less compact urban form, would be adoptable in terms of mitigating PM2.5 concentrations in the GBA urban agglomeration.