Tire particles, perfumes, metals? Extensive study of Toronto air looks at what we're breathing in

Walking down Fort York Boulevard on a fresh, breezy afternoon, scientist Elisabeth Galarneau has no issue pointing out possible sources of air pollution.

The manicured lawns and flower beds? A potential source of airborne pesticides. 

The nearby high-rise apartment buildings? A source of pollutants from both heating and cooling, not to mention the cleaners and personal care products being used inside — remnants of which could be circulating down at street level. 

Charcoal barbecues, restaurant stoves, fire pits, squealing tires, nearby highways? They all contribute to the air Torontonians breathe. 

Now, the first glimpse at an in-depth study conducted by Galarneau and over 100 other scientists looking at winter air quality in Toronto is shedding light on rarely-measured air pollutants across the city, such as microplastics, brake wear chemicals, and metals. 

"We've done this study to kind of look at the whole mixture of what people are exposed to in cities, as well as how that varies from neighbourhood to neighbourhood," said Garlarneau, who works for Environment and Climate Change Canada.

As the principal investigator on the Study of Winter Air Pollution in Toronto, known by the acronym SWAPIT, Galarneau led a group, that included contributors from 11 universities, that collected air samples from across the city over six weeks from January to March 2024. 

Winter is a "typically understudied part of the year" that's known for having cleaner air than the smoggy summers, Galarneau said — making the early results of their work all the more surprising. 

"We thought we would see low concentrations" of pollutants, said Galarneau. Instead, they clocked a number of instances of pollutants heading into moderate or high risk levels on the Air Quality Health Index (AQHI). 

"That air quality health index, I didn't expect to see it exceeded in the winter," she said. 

Another surprise? The degree of variation in air pollution depending on neighbourhood. 

Monitoring sites were placed across Toronto, from Pearson Airport in the west, York University to the north, and University of Toronto Scarborough in the east. One site was even perched on the CN Tower, 275 metres in the air. 

"Some pollutants are quite uniform across the city," Galarneau said. "But other ones are sometimes 40 times higher than the average depending where you're looking." 

The specifics of where air pollution is worse — and by what degree — will be revealed in the next year or so, when the study's peer-reviewed results are published in full.