Commuting Exposures to Particulate Air Pollution in Three Canadian Bus Transit Systems: The Urban Transportation Exposure Study

摘要

Background: Health Canada's Urban Transportation Exposure study was designed to assess levels of air pollution in Canadian transport environments. As Canadians spend approximately 52 minutes of their day commuting, this environment may contribute a larger proportion of their daily exposure to traffic-related air pollution (TRAP)". Identifying factors related to bus commuting TRAP exposure is key to its mitigation. Methods: From 2010-2013, sampling was conducted using personal monitors in bus transit environments of Toronto, Ottawa, and Vancouver. In each city, data were collected during 3-week sampling campaigns in the summer and winter for fine particulate matter (PM2.5), ultrafine particulates (UFPs), and black carbon (BC). Buses were classed as natural gas, electric, hybrid electric/diesel, clean diesel, post 2000 diesel, or pre 2000 diesel. Stations/stops were classed as bus stop, above grade bus station, or below grade / indoor bus station. Particulate air pollution levels were compared between cities, seasons and waiting vs riding. The impact of bus propulsion type and stop/station design on air pollution exposures were evaluated using linear mixed-effect models. Model development included screening for potential confounders such as meteorological factors and land use. Results: Levels of PM2.5, UFPs, and BC were similar between cities and with higher UFPs concentrations observed during winter. In Toronto, bus stations had higher (65%, 95%CI: 48-84%) PM2.5 levels relative to bus stops. Similar differences were seen for BC. Compared to pre-20000 diesels, hybrid electric/diesel buses reduced exposures for PM2.5, UFPs, and BC in all three cities. Conclusions: The personal exposure data collected in this study provides a benchmark of Canadian commuter exposure for bus transit and provides evidence of the potential air quality benefits of ventilating indoor/below grade bus stations and replacing older bus models.