Effect of urban green infrastructure on pedestrian exposure to ultrafine particles: A case study of Guangzhou, China

Traffic emissions, as the dominant source of urban Ultrafine Particles (UFP), pose great potential health risks to pedestrians who commute near busy roads. Green infrastructure is regarded as an effective measure for urban particulate pollution abatement. In this study, two weeks of mobile measurements of pedestrian UFP exposure were performed during morning and evening rush hours, along greenway and sidewalk with and without vegetation barrier near an arterial road. UFP concentration was observed to be 28.7% lower with weakened fluctuations on vegetation barrier sidewalk than on open sidewalk in average, while UFP lung-deposited surface area concentration decreased by 21.1% accordingly. Vegetation mitigated UFP concentration in general, however, locally intense heavy-duty vehicles activities might weaken this effect occasionally. The weekly and diurnal variations of UFP concentration and the greenery effect performance were attributable to the combined effect of practical traffic situations, meteorological conditions, and crowd activities. Gray relational analysis indicated that temperature (gamma = 0.814), relative humidity (gamma = 0.787), traffic volume (gamma = 0.764) and heavy-duty vehicles count (gamma = 0.741) were the top four impact factors on roadside UFP concentration during observation.