A recent article published by The Guardian lists Regina as one of the 10 most polluted cities in the U.S. and Canada, but experts are assuring Regina residents that they can still breathe easy.

The article is based on data broken down by the World Health Organization measuring the amount of ultra-fine particles of less than 2.5 microns (PM2.5) in the air, region by region. Regina is listed as having 14 micrograms per cubic metre of ultra fine particles. The only other Canadian city listed was Courtenay, B.C., with 17mg/m³.

Tom Cahill is a professor emeritus of physics and atmospheric sciences at the University of California. He's the author of the book I Can Breathe Clearly Now: Protecting Yourself from Air Pollution. He said The Guardian's article, including Regina as having dangerous air, is misleading.

"You don't cherry pick a single year to do an analysis like that," said Cahill. The data in the article is from 2013. He added that the U.S. standard is 12mg/m³, and the international standard is 10mg/m³.

Comparing "apples and walruses"

He also said that using the metric PM2.5 to assess dangerous air is flawed.

"The problem with it is it mixes things that are harmful with things that are harmless," he said.

"So much of the stuff you have in mass, let's say from wood smoke, some fine soil dust, things that are really not very harmful at all. But in it, you would have buried things that are very harmful," said Cahill.

"Using PM2.5 mass, as a thing of good or bad, gives you results that are ridiculous ... lots of places have worked hard to take care of things, and when a study like this comes out and mixes say, apples and walruses, as a comparison, you're misleading people," said Cahill.

Michael Brauer, a professor at the University of British Columbia in the Faculty of Medicine's School of Population and Public Health, agrees that Regina got its placement on the list from selective use of data, and it is misleading.

He wrote in an email to CBC that the 2013 measurement of 14mg/m³ was not the correct one to have used, and it really should have been 7mg/m³. He added that the 2014 level was 7mg/m³, and 2015 level was 11mg/m³.

According to Brauer, the higher 2015 levels were driven by high readings in summer that may have been caused by forest fire smoke.

"A single forest fire can buy us an entire year's worth of air pollution, and that can come with a misleading result," said Cahill.

"This kind of study erodes the confidence that people have in what science is telling you that is serious. They're crying wolf," added Cahill.

Brauer said overall, Regina is clean in comparison to other locations in Canada, and very clean compared to the rest of the world.

City's response

The City of Regina said in an email to CBC that they cannot comment on the World Health Organization study, as they do not know the source of their information or the methodology used to reach those conclusions. 

They added that the Province of Saskatchewan studied air quality in Regina in 2012-13 and concluded that air throughout Regina is of a high quality and that Regina is comparable to other cities in Canada in terms of the major compounds that are emitted.

With files from The Afternoon Edition and Jérôme Bergeron