Quantification and Modeling of Black Carbon Exposure for Seattle Commuters
Reynolds, Brooke Leigh
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Background: Exposure to traffic-related air pollution may be elevated during commute trips, but could vary with different transportation microenvironments and commuting behavior. Given the variety of commute options available within urban settings, understanding the potential differences in exposures for different commuter choices has potential implications for health, and may inform individual commuter choices and transportation strategies to reduce exposures. Methods: Black carbon concentrations, a surrogate for traffic-related air pollution, were measured for a stratified selection of commute trips for different transportation modes and for arterial and local roadways in Seattle, WA. Black carbon concentrations were analyzed to develop an exposure model capable of providing an estimate of commute exposure with respect to route characterization, mode of transportation, time of day, and ambient pollution level. Results: Results generated typical black carbon exposures of commuters in the Seattle area differentiated by variables such as commute time, mode, and route. Sampling data was used to generate three exposure models utilizing these variables to predict an average black carbon exposure concentration based on commute characteristics. Regression model predictions of black carbon exposure significantly differed between transit modes; of all modes included in the models, transit tunnel predictions were highest and walking predictions were lowest. Within-mode comparisons indicate BC exposure predictions for arterial routes are higher than predictions for local/residential routes, are higher between the hours of 6-9 am than between the hours of 4-6 pm, and increase with increased ambient PM2.5 levels. Conclusion: Commute mode and route can impact personal exposure to black carbon. Better understanding of exposure differences for commute modes and routes in Seattle could enable commuters the opportunity to alter commute choices to minimize exposure to black carbon, as well as enable cities and municipalities such as Seattle to consider exposure potential when making decisions about public transportation infrastructure, such as bus type, placement of bus stops, or ventilation in transit tunnels.
- Environmental health