That's among the findings from a series of air quality tests performed on Montreal patios.
Ryan Kennedy, a researcher, said he found poor air quality even when there was wind, and there weren't any restrictions blocking the flow of air such as an awning or umbrella.
"I think what's important is for us to remember that tobacco smoke is a Class A carcinogen, and any level of exposure bears a risk," Kennedy, based at Johns Hopkins University in Baltimore, Maryland, said in an interview Saturday.
Anti-tobacco advocates are hoping the findings will help make the case for a patio smoking ban in Quebec, and across the country.
Several provinces have already banned smoking on patios, including Newfoundland, Nova Scotia, and Alberta. Yukon has also introduced a ban, along with a number of municipalities across the country.
Quebec is among the provinces that has so far resisted going that route.
Montreal, in particular, is well-known for its sidewalk cafes and bars and has faced resistance to a ban from bar owners worried about losing patrons.
Flory Doucas, a spokeswoman for the Quebec Anti-Tobacco Coalition, said businesses must learn to adapt, just as they did after smoking was banned inside restaurants and bars.
Doucas said wait staff are especially vulnerable under the current rules.
"In the case of workers, they are walking back and forth across these areas filled with smoke. This is a health issue," she said.
Kennedy said some of the air quality measurements he recorded on patios were on par with levels recorded in Kelowna, B.C. when forest fires ravaged the region a few years ago.
- with files from Helen Moka
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