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Planned urban form has become an important strategy to improve air quality in urban agglomerations (UAs), especially pollution due to PM 2.5 , but the influencing mechanisms are not yet clear. This study explores the relationship between four metrics of urban form (size, fragmentation, shape, and dispersion) as determined by analysis of remotely sensed images at 30-m resolution and PM 2.5 concentrations in 19 Chinese UAs. The influence of level of urban development and season is examined. Five control variables, including population density, temperature, precipitation, wind speed, and the normalized difference vegetation index (NDVI) are selected for use in multiple linear regression models. Size, fragmentation, and shape of urban form, but not dispersion, were found to have significant effects on PM 2.5 concentrations of different urbanization-level UAs. Urban size and fragmentation have stronger impacts on PM 2.5 concentrations in UAs with lower urbanization levels while urban shape has a greater impact in higher-level UAs. In terms of seasonal variation in all UAs, urban form is more pronouncedly associated with PM 2.5 concentrations during spring and autumn than summer and winter. Urban size and fragmentation are positively associated with PM 2.5 concentrations whereas urban shape and dispersion are on the contrary. The relationships between urban form and PM 2.5 uncovered here underscore the importance of urban planning as a tool to minimize PM 2.5 pollution. Specifically, local government should encourage polycentric urban form with lower fragmentation in urban agglomerations. UAs with lower urbanization levels should control the disordered expansion of construction land and higher-level UAs should promote the mix of green land and construction land. Moreover, measures to control air pollution from anthropogenic activities in spring, autumn and winter are likely to be more effective in decreasing PM 2.5 concentrations in UAs. • The urban form was measured by urban size, fragmentation, shape, and dispersion. • Effect of urban form on PM 2.5 concentrations varies with urbanization levels of urban agglomerations. • Seasonally, urban form has a stronger effect on PM 2.5 concentrations in spring and autumn. • Polycentric urban form with lower fragmentation should be encouraged in urban agglomerations for reducing PM 2.5 pollution. [ABSTRACT FROM AUTHOR]