Impacts of multi-scale urban form on PM2.5 concentrations using continuous surface estimates with high-resolution in US metropolitan areas

This study explores the relationship between urban form at the metropolitan and neighborhood scale and fine particulate matter (PM2.5) concentrations by establishing multi-level regression models. This study has different assumptions about urban form depending on the scale used. While at the metropolitan scale, the urban form is related to the change in travel behavior, at the neighborhood scale, it is related to proximate emission sources such as roads, emissions facilities, employment centers, etc. The study shows that at the metropolitan scale, higher urban fragments, population density, and road density are associated with higher PM2.5 concentrations; higher job-resident balance and accessibility to schools are associated with lower PM2.5. At the neighborhood scale, a higher density of the nearby emission sources and higher accessibility to destinations are associated with higher PM2.5 concentrations. Urban fragments and land use mix have consistent impacts on air quality com-pared to preexisting studies. While population density and road density have two conflicting assumptions regarding PM2.5, in this study, the net effect of population density and road density on air quality is negative. Accessibility to destinations has different associations with PM2.5 depending on the scale of urban form measurement. At the metropolitan scale, high accessibility to destinations lessens PM2.5 concentrations by reducing vehicle distance. On the other hand, at the neighborhood scale, high accessibility to destinations makes it close to areas, which concentrate air emissions. We suggest that urban planners and decision-makers establish different strategies depending on urban form types when there are urban development plans.