Air pollution levels are "definitely too high for the public" near major roadways in Canadian cities — especially at rush hour and in winter — and poorly maintained diesel trucks are largely to blame, says the lead author of a new study that monitored pollutants in Vancouver and Toronto over two years.

The study — led by Greg Evans, director of the Southern Ontario Centre for Atmospheric Aerosol Research at the University of Toronto — was motivated by an earlier discovery that nearly 30 per cent of Canadians, including about half of Toronto's residents, live within 250 metres of a major roadway.

Meanwhile, growth in online shopping and delivery is boosting the number of heavy, diesel-powered vehicles cruising through our cities. Freight is the fastest growing sector within transportation , according to the Pembina Institute, a think-tank focused on clean energy.

Diesel exhaust is a human carcinogen. - Greg Evans, University of Toronto

"Diesel exhaust is a human carcinogen," said Evans. "And the concentrations of diesel exhaust exposure that we saw surprised me."

The levels were higher than the allowed exposure for workers in the Netherlands, he said. "That's definitely too high for the public."

The study, done in collaboration with Environment and Climate Change Canada, the Ontario Ministry of the Environment, Conservation and Parks and Metro Vancouver, was released Wednesday.

Pollutants such as nitrogen oxides, ozone, sulphur dioxide and particulates are responsible for 7,700 premature deaths in Canada each year, and deaths and illness due to air pollution cost Canada $36 billion in 2015, according to a 2017 study from the International Institute for Sustainable Development .

Nitrogen dioxide levels measured in the new study mean it will be difficult to achieve the air-quality standards being proposed by the federal government for 2020 next to major roads, Evans said. In fact, it found levels exceeding those standards even 150 metres away from major roads.

About 30 per cent of Canadians live within 250 metres of a major roadway. That includes half the residents of Toronto, such as those living in this condo overlooking the Gardiner Expressway. (Craig Chivers/CBC)

The study recorded roadside levels of black carbon in a range associated with an elevated lifetime risk of lung cancer.

Other major findings of the study were that:

Most of the pollution recorded beside major roads, including 80 per cent of nitrogen monoxide and 60 per cent of black carbon, came from local traffic.

Emissions, especially of nitrogen oxides, were far worse in winter. Evans said that's because vehicle systems designed to reduce those emissions, such as catalytic converters are "really not designed for the Canadian climate" and work poorly in cold temperatures.

"Non-tailpipe" emissions — that is, metal-rich dust from tire and brake wear — increased over two years. That is blamed on the growing popularity of SUVs and pickup trucks , which cause more tire and brake wear because they're heavier. (They also generate more greenhouse gas emissions.)

, which cause more tire and brake wear because they're heavier. (They also generate more greenhouse gas emissions.) Pollution levels weren't directly related to the number of vehicles: One roadway in Vancouver had similar pollution levels to a Toronto portion of Highway 401, which has more than a dozen lanes and carries 10 times more traffic.

"That really changes how we have to think about exposure in cities," Evans said.

Cars make their way along a congested highway in Toronto. Researchers found it's not just the number of vehicles that make a difference: A small truck corridor in Vancouver had pollution levels similar to that of Highway 401 in Toronto, even though it carries 10 times as many vehicles. (Lars Hagberg/The Canadian Press)

The Vancouver road with the unexpectedly high emissions is a major truck route, and a small number of trucks have a disproportionate impact on emissions, the study results suggest.

Targeting trucks

That means reducing people's exposure to pollutants might be a matter of targeting highly polluting trucks, Evans said, and forcing them to be repaired or retrofitted to lower emissions. Or banning them from areas with vulnerable populations, such as near schools and daycares.

At the moment, however, he said there isn't any "adequate" testing of truck emissions while they're actually on the road, and testing in the garage can be easily tampered with , as Volkswagen emissions cheating scandal showed. Nor is there much enforcement.

Additionally, there is "surprisingly little" information about what routes are being used by trucks within cities, Evans said.

His own lab is currently looking into the health effects of the growing "non-tailpipe" emissions noted in the study. Many of those dust particles, the study found, are small enough to be inhaled deeply into the lungs and are rich in metals that can catalyze harmful chemical reactions that could potentially damage the lungs.

"There's no good reason to think these should be less harmful [than other emissions]," said Evans.

Greg Evans, lead author of the new study, looks through some of the equipment in his University of Toronto lab. The study continuously measured air pollutants and traffic at four sites in Toronto and two in Vancouver over two years. (Craig Chivers/CBC)

The study collected data from four monitoring sites in Toronto and two in Vancouver; three were close to roads and three were away from roads. The sites collected local air continuously for two years.

For some pollutants, monitoring was done in real time. For others, samples were sent to a lab in Ottawa for testing. Researchers also recorded traffic levels as the air was being sampled.

Mobile monitoring stations were also used to see how representative the permanent monitoring results were; they recorded similar results.

Most of the results compiled in Wednesday's report have already been published in a dozen peer-reviewed publications that are listed in the report itself.

Workers perform final inspections on 2015 Ford Explorer SUVs. The growing popularity of such heavier vehicles over smaller cars is being blamed for an increase in harmful polluting dust from brake and tire wear. (M. Spencer Green/Associated Press)

The study was a pilot that shows how to do this kind of monitoring and what kind of information can be gained from it, Evans said. He hopes it will lead to a larger, more permanent network of air pollution monitoring stations that includes other provinces.

A new station has already been set up in Quebec City, and others are being considered for Montreal and Edmonton.

Carolyn Kim, director of transportation and urban solutions at the Pembina Institute, said the study's results highlight the potential health benefits of reducing air pollution and greenhouse gas emissions.

Kim, who was not involved in the study, said this kind of research helps provide a "sense of urgency" for policy-makers to address such concerns.

She noted that freight emissions are going up, due to changing consumer preferences and habits such as online shopping and same-day delivery, and are expected to surpass passenger-related emissions by 2030.

"I think there's an opportunity to electrify those vehicles so we're decreasing our emissions from freight," Kim said. "That's one way of addressing the small contingent of vehicles that are emitting the highest amounts of air pollution and greenhouse gas emissions."