Air quality variability near a highway in a complex urban environment

In response to growing public health concerns regarding elevated air pollutant exposures and adverse human health effects for near-road populations, a study was conducted to assess how complex urban roadway configurations affect local-scale air quality. This study combined fixed-site and mobile air quality measurements with laboratory wind tunnel experiments to examine how the transport and dispersion of traffic-emitted pollutants varies with changing roadway configuration, notably with at-grade and cut section designs. Results of the study indicated that short-term maximum concentrations occurred with measurements made along at-grade locations, however, average concentrations tended to be higher at the top of the cut section compared with the at-grade location, most often occurring during lower air pollutant events. Wind flow and NO2/NOx ratios indicated that the cut section moderated peak concentrations through increased transport and dispersion, as well as reducing the influence of turbulence from vehicle activity near the road. The at-grade locations also experienced a higher impact from primary vehicle emissions than those measurements made at similar distances along a cut section. Mobile monitoring suggested that these peak concentrations quickly conformed to concentration levels measured near cut sections within 50–100 m of the source highway. Wind tunnel simulations of the study site with and without the cut section present indicated that the cut section reduced the concentrations of primary emitted vehicle pollutants by 15–25 percent for receptors located approximately 20 m from the highway. The wind tunnel simulations also revealed that buildings and other urban features influenced local-scale pollutant transport and need to be considered when evaluating near-road air quality.

► We measure and model CO and NO2 pollutant concentrations along a complex urban highway.
► Peak concentrations occurred with at-grade design, averages higher with cut section.
► Wind tunnel showed 15–25% decrease for perpendicular winds with cut sections.
► Complexity of road design highly influenced near-road concentrations.
► The results show how urban features influence near-road population exposures.