Bus commuter exposure and the impact of switching from diesel to biodiesel for routes of complex urban geometry

• Published in: Environmental pollution (1987) Vol. 263; no. Pt A; p. 114601
• Main Authors: Targino, Admir Créso, Krecl, Patricia, Cipoli, Yago Alonso, Oukawa, Gabriel Yoshikazu, Monroy, David Andrés
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-08-2020
• Subjects: Air Pollutants - analysis; Biofuels; Black carbon; Brazil; BRT; Cities; Environmental Monitoring; Motor Vehicles; Particulate Matter - analysis; PM2.5; Short-lived climate pollutants; Ultrafine particles; Vehicle Emissions - analysis; Brazil; Cities; Ultrafine particles; Short-lived climate pollutants; BRT; Black carbon; PM2.5; PM(2.5)
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2020.114601

We report on commuters’ exposure to black carbon (BC), PM2.5 and particle number (PN, with aerodynamic diameter, da, in the range 0.01 <da< 1.0 μm) collected on-board diesel- and biodiesel-fuelled buses of the Bus Rapid Transit (BRT) system of the city of Curitiba, Brazil. Particulate concentrations measured at high sampling rates allowed the capture of fine gradients along the route and the comparison of in-cabin air pollution on buses of different technologies.
Of all metrics, BC showed the largest discrepancies, with mean concentrations of 20.1 ± 20.0 μg m−3 and 3.9 ± 26.0 μg m−3 on diesel- and biodiesel-fuelled buses, respectively. Mean PM2.5 concentrations were similar (31.6 ± 28.5 μg m−3 and 29.0 ± 17.8 μg m−3), whilst mean PN concentrations were larger on the biodiesel buses (56,697 ± 26,800 # cm−3vs. 43,322 ± 32,243 # cm−3). The results are in line with studies on biodiesel emission factors that reported lower BC mass but more particles with smaller diameters. Our hypothesis is that different emission factors of diesel and biodiesel engines reflected in differences of in-cabin particulate concentrations. We found that the passenger exposure during the bus commutes was affected not only by the fuel used but also by the street geometry along the route, with segments with canyon configurations resulting in peak exposure to particulates. The results suggest that i) switching from diesel to biodiesel may help abate commuters’ exposure to BC particles on-board buses of the BRT system, whilst it would need to be complemented with after-treatment technologies to reduce emissions; ii) further reductions in exposure (to peaks in particular) could be achieved by changing bus routes to ones that avoid passing through narrow urban street canyons.
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•In-cabin PM concentrations were linked to type of fuel and street geometry.•Mean black carbon concentration was lower on biodiesel than on diesel buses.•Mean particle number concentration was higher on biodiesel than on diesel buses.•Mean in-cabin PM2.5 concentration showed no statistically significant differences.•Peak in-cabin PM concentrations persisted in canyons regardless of the fuel used.