title: A comparison of exposure metrics for traffic-related air pollutants: application to epidemiology studies in Detroit, Michigan.
abstract: Vehicles are major sources of air pollutant emissions, and individuals living near large roads endure high exposures and health risks associated with traffic-related air pollutants. Air pollution epidemiology, health risk, environmental justice, and transportation planning studies would all benefit from an improved understanding of the key information and metrics needed to assess exposures, as well as the strengths and limitations of alternate exposure metrics. This study develops and evaluates several metrics for characterizing exposure to traffic-related air pollutants for the 218 residential locations of participants in the NEXUS epidemiology study conducted in Detroit (MI, USA). Exposure metrics included proximity to major roads, traffic volume, vehicle mix, traffic density, vehicle exhaust emissions density, and pollutant concentrations predicted by dispersion models. Results presented for each metric include comparisons of exposure distributions, spatial variability, intraclass correlation, concordance and discordance rates, and overall strengths and limitations. While showing some agreement, the simple categorical and proximity classifications (e.g., high diesel/low diesel traffic roads and distance from major roads) do not reflect the range and overlap of exposures seen in the other metrics. Information provided by the traffic density metric, defined as the number of kilometers traveled (VKT) per day within a 300 m buffer around each home, was reasonably consistent with the more sophisticated metrics. Dispersion modeling provided spatially- and temporally-resolved concentrations, along with apportionments that separated concentrations due to traffic emissions and other sources. While several of the exposure metrics showed broad agreement, including traffic density, emissions density and modeled concentrations, these alternatives still produced exposure classifications that differed for a substantial fraction of study participants, e.g., from 20% to 50% of homes, depending on the metric, would be incorrectly classified into "low", "medium" or "high" traffic exposure classes. These and other results suggest the potential for exposure misclassification and the need for refined and validated exposure metrics. While data and computational demands for dispersion modeling of traffic emissions are non-trivial concerns, once established, dispersion modeling systems can provide exposure information for both on- and near-road environments that would benefit future traffic-related assessments.
authors.affiliation: Department of Environmental Health Sciences, School of Public Health, University of Michigan, 1420 Washington Heights, Ann Arbor, MI 48109, USA. stuartb@umich.edu.
authors.forename: Stuart
authors.initials: S
authors.lastname: Batterman
authors.affiliation: National Exposure Research Laboratory, U.S. Environmental Protection Agency, 109 T.W. Alexander Drive, Research Triangle Park, NC 27711, USA.
authors.forename: Janet
authors.initials: J
authors.lastname: Burke
authors.affiliation: National Exposure Research Laboratory, U.S. Environmental Protection Agency, 109 T.W. Alexander Drive, Research Triangle Park, NC 27711, USA. isakov.vlad@epa.gov.
authors.forename: Vlad
authors.initials: V
authors.lastname: Isakov
authors.affiliation: Department of Pediatric Pulmonary, Medical School, University of Michigan, 1500 East Medical Center Drive, Ann Arbor, MI 48109, USA. tobyl@med.umich.edu.
authors.forename: Toby
authors.initials: T
authors.lastname: Lewis
authors.affiliation: Department of Biostatistics, School of Public Health, University of Michigan, 1420 Washington Heights, Ann Arbor, MI 48109, USA. bhramar@umich.edu.
authors.forename: Bhramar
authors.initials: B
authors.lastname: Mukherjee
authors.affiliation: Department of Environmental Health Sciences, School of Public Health, University of Michigan, 1420 Washington Heights, Ann Arbor, MI 48109, USA. trobins@umich.edu.
authors.forename: Thomas
authors.initials: T
authors.lastname: Robins
mesh_terms: D000293:Adolescent; D000393:Air Pollutants / Q000032:analysis*; D002648:Child; D002947:Cities; D004781:Environmental Exposure; D004784:Environmental Monitoring / Q000379:methods*; D016021:Epidemiologic Studies; D006801:Humans; D008824:Michigan; D008962:Models, Theoretical; D001335:Vehicle Emissions / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D001335:Vehicle Emissions