The ratio of effective building height to street width governs dispersion of local vehicle emissions

Analysis of data collected in street canyons located in Hanover, Germany and Los Angeles, USA, suggests that street-level concentrations of vehicle-related pollutants can be estimated with a model that assumes that vertical turbulent transport of emissions dominates the governing processes. The dispersion model relates surface concentrations to traffic flow rate, the effective aspect ratio of the street, and roof level turbulence. The dispersion model indicates that magnification of concentrations relative to those in the absence of buildings is most sensitive to the aspect ratio of the street, which is the ratio of the effective height of the buildings on the street to the width of the street. This result can be useful in the design of transit oriented developments that increase building density to reduce emissions from transportation.