Understanding the Impact of Built Environment on Air Quality in Transit Oriented Developments

Transit Oriented Developments (TODs) are designed to promote walking, cycling, and public transportation to reduce motor vehicle emissions by increasing the density of people through the use of multi-story buildings. In principle, TODs should improve local air quality, but the effect of these multi-story buildings on dispersion within the urban canopy is not yet known. Thus, we are conducting a field study to investigate the impact of building morphology on local air quality in TODs. We are making stationary particle concentration measurements at the sidewalks and mobile measurements from a vehicle driving on the street. This paper presents the resulting measurements and our analysis of the concentrations in different built environments. To compare the effect of building morphology on dispersion, we must separate the local and background contribution. This is challenging because the background concentration varies with time and the particle emission factor is uncertain. We present an analysis in which we use particle concentrations measured simultaneously on both side of the street to determine the local contribution. The concentration peaks present in the time series also provide us insightful information on the effect of the local built environment on dispersion because they represent the direct contribution of local emission sources. We also compared the concentrations measured within the street and on the sidewalks to estimate the dispersion.