Exploring the effects of 3D urban form on urban air quality: Evidence from fifteen megacities in China

Poor urban air quality, as a long-term and intangible health hazard, has drawn much attention worldwide. Current literature has revealed the significant effects of urban form on air quality, which, however, centers on two-dimensional (2D) features of urban fabric and lacks fine-scale investigations. The impacts of threedimensional (3D) urban form on the concentration and dispersion of air pollutants, such as the height or volume of buildings, still remains unclear. The present work quantified 3D urban form based on Conzen's townscape framework and examined how and to what extent 3D urban form affects air quality at street block level using evidence from fifteen megacities in China. The average concentrations of PM2.5, PM10, NO2, CO, O-3, and SO2 were calculated for different periods of the day, seasons, and years. Our results identified the varied effects of urban form indicators for different air pollutants and times and revealed neighboring effects of building height and density. In particular, accessibility, intersection densities, adjacent block pattern, building arrangement, building density, and land use function have significant effects, and the morphological categories of surrounding blocks tend to be related to different pollution levels. This study provides insights into how to optimize urban form to alleviate air pollution.