A travel mode comparison of commuters’ exposures to air pollutants in Barcelona Audrey de Nazelle a, b, c, * ,1 , Scott Fruin d,1 , Dane Westerdahl e , David Martinez a, b, c , Anna Ripoll f , Nadine Kubesch a, b, c , Mark Nieuwenhuijsen a, b, c a Center for Research in Environmental Epidemiology (CREAL), Barcelona, Spain b Municipal Institute of Medical Research (IMIM-Hospital del Mar), Barcelona, Spain c CIBER Epidemiologia y Salud Pública (CIBERESP), Barcelona, Spain d Department of Preventive Medicine, University of Southern California, Keck School of Medicine, LA, USA e Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY, USA f Institute of Environmental Assessment and Water Research (IDAEA-CSIC), Barcelona, Spain 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 2e3 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. article info Article history: Received 1 March 2012 Received in revised form 2 May 2012 Accepted 7 May 2012 Keywords: Travel mode Traffic air pollution Inhalation dose Active transportation Near-road exposure 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 (PM 2.5 ) and carbon dioxide (CO 2 ) 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 CO 2 to 25 for CO and were 2e3 for PM 2.5 , BC, and UFP. In multivariate analyses, travel mode explained the greatest variability in travel exposures, from 8% for PM 2.5 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 e50% 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. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Daily travel may contribute a disproportionate fraction of the overall inhalation of air pollutants for urban populations, and may vary considerably according to the travel mode choice. Due to the proximity to traffic, transportation microenvironments can exhibit relatively high concentrations, which are compounded by high inhalation rates in the case of active travel (walking and cycling). Traffic-source air contaminants, furthermore, tend to reach their peak during typical morning commute times (Moreno et al., 2009). Evidence from toxicological and experimental studies indicates that these short bursts of high pollutant intakes may have dispro- portionate health impacts (Michaels and Kleinman, 2000). Studies * Corresponding author. Center for Research in Environmental Epidemiology (CREAL), Barcelona, Spain. E-mail addresses: anazelle@gmail.com, anazelle@creal.cat (A. de Nazelle), fruin@usc.edu (S. Fruin). 1 Co-first authors. Contents lists available at SciVerse ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2012.05.013 Atmospheric Environment 59 (2012) 151e159