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Canadian study finds commuters may be exposed to increased levels of traffic-related pollution

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



It is a sign of the times. This need to have a study to tell us the obvious is the result of denial of truth by those that have economic agendas. It is simply to place additional barriers in the way of knowledge dissemination. Did anyone really need a study to convince them that this is real. If so, then these people or person are really dim or really dishonest, because an intelligent and honest person would simply observe the obvious.


Reminds me of multiple studies on health hazards from tobacco smoking. It was also so obvious and denied for many decades.

We still have about 25% deniers about smoking and 90% deniers about ICEVs harmful pollution emissions.

The majority is very slow to change?

Schools and doctors could help but they do not want to get involved because they could lose financial and other gifts from you know who.


So, people in traffic are exposed to higher levels of traffic-related pollution. As opposed to, what? People who are NOT in traffic? The Canadians actually had to have a study to determine this?
Canada, why do we let you be a country?


Envy will not improve your lot


To those who are pretending not to understand: it's not the fact of traffic pollution that's at issue, it's the amount and the type.
Remember that Canada has publicly funded health care, so questions such as "would it make sense to divert heavy trucks during rush hour in order to prevent cancers?" make economic sense. The only way to answer this type of question is with hard data, and this study is part of that process.

Ask yourselves "would you save more lives/money by tightening diesel emission controls, or by extending regional train service?" or "should heavy trucks be allowed on toll/express roads?" It's really hard to answer either question without hard data.


Not so long ago our city had a few hundred aluminum and
electric trolley buses. Then came US GM with its heavier diesel city buses and bonuses for local politicians.

After 5 plus decades with heavy steel polluting diesel city buses we will progressively return to cleaner lighter hybrid and electric city buses between 2017 and 2030.

We need more by-pass highways to keep dirty diesel cargo trucks further away from city centre.

The sea port will be moved about 35 Km downstream. That will help to further reduce truck and rail traffic from city centre.

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