Evaluating pedestrian exposure to traffic-related airborne particles: Insights for sustainable and healthier urban environments

Vehicular traffic is a major source of urban air pollution in Southeast Asia (SEA), posing significant health risks to pedestrians due to exposure to fine particulate matter (PM_2.5), black carbon (BC), and ultrafine particles (UFPs). Despite this issue of health concern, limited data exists linking the spatial and temporal variations of these pollutants and related pedestrian exposure in the region. Due to the unique urban topography, road infrastructure, and meteorological conditions in SEA, high-resolution air quality monitoring studies are essential to better understand pedestrian exposure patterns. This study addresses this knowledge gap by conducting a comprehensive real-time mobile measurement campaign in Singapore as a case study, using portable instruments to assess pedestrian exposure to the traffic-derived air pollutants across diverse urban road categories. We developed three land-use regression (LUR) models to identify the determinants and spatial distributions of PM_2.5, BC, and UFP concentrations along the pedestrian pathways. Unlike previous stationary or vehicular-based LUR studies, our walking-based approach represents an effective assessment of pedestrian exposure. The results showed mean levels of PM_2.5, BC and UFPs ranged from 16.4 to 20.0 μg m⁻³, 2.2–5.8 μg m⁻³ and 11.3 × 10³ to 31.7 × 10³ # cm^-3, respectively, with BC and UFPs more strongly correlated with vehicular traffic emissions than PM_2.5, particularly near highways and major arterial roads. Urban greenery, including tree density and park areas, was found to significantly reduce pedestrian exposure. These findings provide insights into the relationship between urban design, traffic patterns, and pedestrian health, offering strategies to mitigate traffic-related air pollution and promote healthier cities in SEA.