Air Pollution Caused by Urban Transport: Meteorology and Downwind Dispersion of Near-Road Traffic Exhaust and Non-Exhaust Emissions
摘要
Traffic emissions, including exhaust and non-exhaust sources, are major contributors to urban air pollution, with disproportionate health impacts on low-income and marginalized communities living or working near high-traffic corridors. This study examines the dispersion of PM2.5 and PM10 from traffic-related emissions in Kigali, Rwanda, a rapidly urbanizing city, for the year 2022. Emissions rates were quantified using traffic volume and road characteristics, while dispersion was simulated with a Gaussian plume model (AERMOD) and validated against ground-based measurements across multiple downwind distances. Results revealed heavy-duty diesel vehicles are the primary source of PM2.5 (501 µg/s) and PM10 (935 µg/s) emissions rates (combined exhaust and non-exhaust), peaking during the evening rush hour (16:00–18:00). Ground-based monitoring identified elevated PM levels downwind, with PM2.5 and PM10 peaking at 48 µg/m3 and 55 µg/m3 at the furthest site (4.97 km), influenced by easterly and southeasterly atmospheric circulation at moderate wind speeds (2–3.5 m/s) and nearby local additional sources like residential emissions. AERMOD simulations predicted peak daily concentrations of 41.7 µg/m3 for PM2.5 and 73.7 µg/m3 for PM₁₀ near roads (0.20 km), with annual averages of 14.9 µg/m3 and 22.7 µg/m3, respectively. Model performed well near roads (e.g., at 0.24 km: FB = 0.0, NMSE = 0.0, FAC2 = 1.0) but underestimated concentrations further downwind, highlighting challenges in representing complex local sources. Findings highlight persistent pollution risks in cities like Kigali from traffic emissions and dispersed sources, emphasizing the global need for strengthened emission controls, strategic urban planning near roadways, and context-specific air quality policies in rapidly urbanizing settings.