Project Summary
Southern California is no stranger to auto-related pollution. Areas near roadways typically demonstrate much higher pollutant concentrations; as a result, pedestrians and residents in these areas face greater exposure to air pollutants. In dense urban areas like Los Angeles, near-roadway environments can include most street-level outdoor spaces. At the same time, traffic-related pollution levels in urban areas are highly variable. Although the connection between built environment and street-level pollutant concentrations is a nascent field of study, it is clear that the design of the built environment plays a major role on pollution concentration.
The researchers examined the effects of different built environment designs on the concentrations of street-level ultrafine particles (UFP) at the scale of several blocks using the Quick Urban and Industrial Complex (QUIC) numerical modeling system. They evaluated the effects of several built environment designs, changing building heights and spacing while holding total built environment volumes constant. They found that ground-level open space reduces street-level pollutant concentrations. Holding volume/surface area constant, tall buildings clustered together with larger open spaces between buildings resulted in substantially lower pollutant concentrations than buildings in rows. Buildings arranged on a ‘checkerboard’ grid with smaller contiguous open spaces, a configuration with some open space on one of the sides of the roadway at all locations, resulted in the lowest average concentrations for almost all wind directions. Rows usually prohibit mixing for perpendicular and oblique wind directions, even when there are large spaces between them, and clustered buildings have some areas where buildings border both sides of the roadways, inhibiting mixing. The model results suggest that pollutant concentrations drop off rapidly with height in the first 10 m or so above the roadways. In addition, the simulated vertical concentration profiles show a moderate elevated peak at the roof levels of the shorter buildings within the area. Model limitations and suggestions both for urban design are both discussed.
