Variability of traffic-related air pollutants at two- and four-phase intersections

Traffic intersections are the hotspots of air pollution. However, pollutant variation patterns at signalized intersections remain less explored. In this study, field measurements were conducted to investigate the pollutant variability at two- and four-phase intersections in Beijing, China. Spikes were frequently observed in pollutant concentrations at a fine-temporal (1-HZ) scale that could be well-characterized using Gaussian peak functions. The mean pollutant concentrations at two-phase intersections peaked under the green signal light and decreased exponentially under the red signal light. Pollutant concentrations were significantly influenced by the signal control pattern, which higher pollutant concentrations were observed during the pedestrian-waiting phase at the two-phase intersection and during the cross-walking phase at the four-phase intersection. Additionally, intersections with shorter signal light times result in insufficient pollutant dispersion and more frequent stop-andgo by vehicles. Nevertheless, the traffic volume is the dominant factor for a higher pollution level. These results broaden our knowledge of pollutant variability at signalized intersections and have implications for the mitigation of traffic-related air pollution.