Canada has a better way to measure smoky air. Ontario doesn’t use it

The federal government recently updated its air quality index to better reflect the threat of wildfire smoke — but Ontario is not using the improved system, creating gaps between the information available to the public and the actual health risks.

As of 1 p.m. Wednesday, concentrations in eastern Toronto of particulate matter — a dangerous form of air pollution linked to a litany of short- and long-term health problems — were measured at nearly 100. That’s according to raw data from a county monitoring station, which each hours is posted online. Levels that are high pose health risks to anyone, regardless of age or pre-existing conditions.

But the Air Quality Health Index (AQHI) in eastern Toronto at the time was at 5, or “moderate” – a category indicating that the general population should not be concerned about usual outdoor activities, while high-risk groups, such as children and people with respiratory illnesses, should only “consider” making a new appointment.

As large parts of Canada continue to grapple with severe air pollution caused by an unprecedented wildfire season, the AQHI is suddenly under close scrutiny by people making health decisions for themselves and others, said Environment and Climate Change Canada’s Céline Audette.

“The daycares, the retirement homes, all those facilities that care for our people at risk,” said Audette, a policy analyst in health and air quality forecasting services. “They’re paying attention.”

Environment Canada’s new, improved index is taken from British Columbia, a province with a long history of dealing with smoke. During a particularly bad wildfire summer in BC, both scientists and the public recognized that the AQHI did not reflect actual conditions on the ground.

“We need to understand that the AQHI was not originally designed to reflect wildfire risks. It was designed to reflect air pollution risks in cities,” said Sarah Henderson, scientific director of Environmental Health Services at the British Columbia Center for Disease Control.

Historically, the AQHI was calculated using concentrations of three types of unhealthy air pollutants: nitrogen dioxide, ground-level ozone, and particulate matter, or PM2.5. During a typical urban smog day, these three pollutants tend to build up slowly and hang like a dome. The two pollutants that the index weights heaviest in its final risk score are nitrogen dioxide and ozone, and it uses an average of three hours to represent this slower-growing threat.

“Wildfire smoke is a whole different ball game,” explains Henderson.

Plumes of wildfire smoke arrive and dissipate unpredictably, causing sudden, rapid spikes in pollution. Neither nitrogen dioxide nor ozone is particularly relevant during wildfires. The big risk comes from PM2.5, the third pollutant on which the AQHI depends, which can suddenly skyrocket while the other two remain flat – just as Toronto saw Wednesday afternoon.

Part of what motivated BC to update its air quality index was that the public noticed this mismatch, Henderson said.

“People said to us, ‘Hey, it’s smoky in my community and the AQHI is a 2. What’s going on?’ “People lost faith in the best tool we have to communicate about air quality as health risks. We didn’t want that to happen.”

For scientists like Henderson, the other main motivation was that their own research showed that most of the risk during these smoky wildfire days occurred quickly, within the first hour of a spike in PM2.5 levels. The province needed a system that responded more quickly.

BC’s AQHI now calculates two scores simultaneously: the three-hour average of the top three pollutants, the mix commonly encountered during a city smog day; and the hourly average of particulate matter alone, which better represents smoke from wildfires. What results in the higher AQHI score is the one the public sees.

In 2020, Canada began rolling out this enhanced AQHI across the country, Audette said.

“Some of the smaller provinces that have less policy to implement the new formula were able to implement it immediately. We are still working with some of the other partners, and they are working with their senior management to implement it in their jurisdictions.”

A spokesperson for the Ontario Ministry of the Environment did not answer questions about why the province has not adopted the enhanced AQHI or when it plans to do so.

“Ontario is currently working with Environment and Climate Change Canada evaluating options for enhancing the AQHI program with a PM2.5 trigger, in addition to the current process of using the cumulative effects of ozone, nitrogen dioxide and particulate matter. ‘ wrote Gary Wheeler.

Alberta already uses an improved air quality index that overrides the result of mixed pollutants when a single reading skyrockets, but uses a different formula; the province is considering switching to the federal system, a spokesman said. Quebec uses a different system that reports PM2.5 directly.

Audette urged Canadians to continue paying attention to the AQHI, but also to look out for special air quality statements, which are issued directly by Environment Canada: “once there is a special air quality statement, that is your confirmation that there is a real problem.

“It’s staggering right now,” she added. “We’ve never been in this situation before.”

Kate Allen is a Toronto-based reporter covering climate change for the Star. Follow her on Twitter: @catecallen

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