A travel mode comparison of commuters' exposures to air pollutants in Barcelona: Fid-Bau Portal

A travel mode comparison of commuters' exposures to air pollutants in Barcelona

de Nazelle, Audrey / Fruin, Scott / Westerdahl, Dane / Martinez, David / Ripoll, Anna / Kubesch, Nadine / Nieuwenhuijsen, Mark

Abstract

Abstract Daily commutes may contribute disproportionately to overall daily inhalations of urban air contaminants. Understanding factors that explain variability of exposures during travel, and especially differences across transportation modes, is essential to accurately assess health impacts of traffic emissions and to develop effective mitigating measures. We evaluated exposures and inhaled doses of air pollution and assessed factors that contributed to their variability in different travel modes in Barcelona. Black carbon (BC), ultrafine particles (UFP), carbon monoxide (CO), fine particle mass (PM2.5) and carbon dioxide (CO2) were measured and compared across walk, bike, bus, and car modes for a total of 172 trips made on two different round trip routes. On average, the car mode experienced highest concentrations for all contaminants. In pairwise t-tests between concurrent mode runs, statistically significant differences were found for cars compared to walking and biking. Car-to-walk or car-to-bike concentration ratios ranged from 1.3 for CO2 to 25 for CO and were 2–3 for PM2.5, BC, and UFP. In multivariate analyses, travel mode explained the greatest variability in travel exposures, from 8% for PM2.5 to 70% for CO. Different modal patterns emerged when estimating daily inhaled dose, with active commuters' two to three times greater total inhalation volume during travel producing about equal UFP and BC daily inhaled doses to car commuters and 33–50% higher UFP and BC doses compared to bus commuters. These findings, however, are specific to the bike and pedestrian lanes in this study being immediately adjacent to the roadways measured. Dedicated bike or pedestrian routes away from traffic would lead to lower active travel doses.

Highlights ► We measured air pollution in travel microenvironments in a Southern European city. ► Travel modes explained much more of commuters' exposure variability than meteorology. ► Particulate pollutants in cars were 2–3 times higher than in active modes (walk, bike). ► Contrasts between modes were greatest for primary pollutants (CO then BC and UFP). ► Accounting for inhalation rate differences, pedestrians and cyclists pollution doses were comparable to car drivers.