A study by researchers led by a team from the Air Health Science Division of Health Canada (the Federal department responsible for helping Canadians maintain and improve their health) finds that commuters may be exposed to increased levels of traffic-related air pollution owing to close proximity to traffic-emissions. The study also found that traffic characteristics, land use, road types, and meteorology are important determinants of these exposures.
As reported in their papaer in the ACS journal Environmental Science & Technology, the team collected in-vehicle and roof-top air pollution measurements over 238 commutes in Montreal, Toronto, and Vancouver, Canada between 2010 and 2013. They used voice recordings to collect real-time information on traffic density and the presence of diesel vehicles; multivariable linear regression models were used to estimate the impact of these factors on in-vehicle pollutant concentrations (and indoor/outdoor ratios) along with parameters for road type, land use, and meteorology.
In-vehicle PM2.5 and NO2 concentrations consistently exceeded regional outdoor levels and each unit increase in the rate of encountering diesel vehicles (count/min) was associated with substantial increases (>100%) in in-vehicle concentrations of ultrafine particles (UFPs), black carbon, and PM2.5 as well as strong increases (>15%) in indoor/outdoor ratios.
In urban areas, traffic is a major source of ambient air pollution and may represent an important source of exposure for commuters owing to their close proximity to traffic emissions. Indeed, for some pollutants such as ultrafine particles (UFPs) (≤0.1 μm) and black carbon, exposures during daily commutes may represent a large portion of overall daily exposure levels despite relatively short time periods spent in commuting environments. Moreover, evidence from several short-term panel studies suggests that in-vehicle exposures may contribute to increased systemic inflammation, pulmonary inflammation, oxidative stress, and changes in cardiac autonomic modulation. As a result, there is currently a need to understand determinants of these exposures in order to evaluate their potential health impacts in large-scale population-based studies.
The Urban Transportation Exposure Study [UTES] was designed to characterize commuter exposures to traffic-related air pollutants in Canadian metropolitan areas including particulate air pollutants such as UFPs, black carbon, and fine particulate matter air pollution below a median aerodynamic diameter of 2.5 μm (PM2.5), as well as nitrogen dioxide (NO2) and volatile organic compounds (VOCs). In addition, models were developed to estimate the potential impacts of traffic characteristics, road types, land use, and meteorological factors on in-vehicle particulate air pollutant concentrations (and indoor/outdoor ratios) along various routes in these regions. This is the first national study of in-vehicle commuter exposures in Canada and to our knowledge is the first to use land use characteristics to predict in-vehicle concentrations along a given route.—Weichenthal et al.
The UTES was conducted between 2010 and 2013 in Canada’s three largest cities: Toronto, Ontario; Montreal, Québec; and Vancouver, British Columbia. Air pollution monitoring took place twice each day during the morning (7:00−10:00) and evening (15:00−18:00) rush hour periods.
Three separate vehicles monitored air pollution concentrations during each route with each vehicle focusing on specific portions of the city: downtown areas, major highways, and suburban areas. Dedicated routes were not assigned; instead, drivers focused on maximizing coverage of these three specific regions during each sampling period. Drivers took a different path along their route each day in order to avoid encountering the same regions at the same time during each commute.
In general, our findings suggest that Canadian vehicle commuters may be repeatedly exposed to elevated levels of traffic-related air pollutants and that traffic characteristics, land use, road type, and meteorology are important determinants of these exposures. Models based on these factors may be useful in population-based studies interested in capturing in-vehicle air pollution exposures as a compliment to residential exposure estimates.—Weichenthal et al.
Scott Weichenthal, Keith Van Ryswyk, Ryan Kulka, Liu Sun, Lance Wallace, and Lawrence Joseph (2014) “In-Vehicle Exposures to Particulate Air Pollution in Canadian Metropolitan Areas: The Urban Transportation Exposure Study,” Environmental Science & Technology doi: 10.1021/es504043a