Your Neighborhood Has Its Own Very Special Cocktail of Toxic Air Pollution

​Pops used to call Toronto the "Big Smoke" because he's an Old and a farmer, and also because Toronto's air is really polluted. But, despite my dad's weirdly non-specific nickname for Toronto, new research from the 6 (sorry) shows that it's not just the city you live in that determines how many potentially harmful emissions you're ingesting—it also depends on how many roads you live near, and the type.

According to new research from the University of Toronto, a person who lives near multiple high-traffic roads may be exposed to more pollution than someone in the middle of nowhere who lives near just one, even if its a highway. That might sound obvious,but it's not a hard and fast rule. Even within a city, the level of pollution is highly variable.

This is because of highly localized concentrations of "ultrafine particles" from vehicle tailpipes. While these particles produce a good amount of pollution near the source, they become less concentrated and hence less harmful when they travel 280 meters from a highway or major road. Because of these particles' highly local nature, one neighbourhood may experience less pollution than another just a few blocks away depending on the traffic levels and types of vehicles in it. The levels may even change hour by hour.

"Some areas will be exposed to very high concentrations [of ultrafine particles] if they live around that range, but if the household is located further, the concentration is almost zero," Cheol-Heong Jeong, lead author of the paper, told me. "The variation is so high that usually, in the morning you'll have a high spike of ultrafine particles, and in the middle of the day, a little bit lower. That also increases in the evening rush hour."

These ultrafine particles are different from the large and medium-sized molecules—which come from sources such as traffic and industry—that form a relatively homogenous distribution of pollution across a city-wide area.

To do the research, Jeong said that the team drove around Toronto in a giant van packed full of highly sensitive instruments. They measured ultrafine particle levels from the time they exited nearby tailpipes until they dissipated. They were literally chasing cars.

"We were chasing heavy emitters—heavy-duty trucks," said Jeong. "It was kind of undercover, like police, waiting for the truck. We would see that the plume was coming out of it, and chase it, taking measurements."

The work is a step forward for research into ultrafine particles; previous studies indicated that ultrafine particles return to background levels after travelling 300 metres away from their point of origin. But by demonstrating that ultrafine particles can still exist in relatively high concentrations at this range, Jeong and his colleagues have shown that more people could actually be at risk.

"The ultrafine particles are particularly troubling," says Greg Evans, another of the study's authors, in a statement. "Because they are over 1000 times smaller than the width of a human hair, they have a greater ability to penetrate deeper within the lung and travel in the body."

According to Jeong, one third of Canadians live within a 280 metre range from at least one major roadway, where UFP concentrations are still double what they normally would be.

Of course, their work doesn't mean that we should forget about city-wide pollution and focus on micro-scale measurement instead. Rather, Jeong said we need a combination of methods. "We need some kind of modelling to predict city-wide concentration," he explained. "So, we measure at the micro-scale, along with some modelling, projecting, and forecasting."

Which reminds me, I should really be riding my bike more often.