Canada has a better way to measure smoky air. Ontario’s not using it

The federal government recently updated its air quality index to better reflect the threat posed by wildfire smoke — but Ontario isn’t using the improved system, leaving gaps between the information available to the public and the true health risks.

By 1 p.m. Wednesday, concentrations in east Toronto of fine particulate matter — a dangerous form of air pollution linked to a litany of both short- and long-term health problems — measured at almost 100. That’s according to raw data from a provincial monitoring station, which is posted online hourly. Levels that high present health risks for everyone, regardless of age or pre-existing conditions.

But the Air Quality Health Index (AQHI) in east Toronto at the time sat at 5, or “moderate” — a category that indicates that the general population does not need to worry about usual outdoor activities, while high-risk groups, like children and people with respiratory conditions, should only “consider” rescheduling.

As large swaths of Canada continue to struggle with severe air pollution caused by an unprecedented wildfire season, the AQHI is suddenly being watched closely by people making health decisions for themselves and others, said Céline Audette, of Environment and Climate Change Canada.

“The daycares, the seniors homes, all those facilities that take care of our people at risk,” said Audette, a policy analyst in health and air quality forecast services. “They are paying attention.”

Environment Canada’s new, enhanced index was adopted from British Columbia — a province that has racked up a lot of experience with smoke. During one particularly bad wildfire summer in B.C., scientists and the public alike both recognized that the AQHI was not matching the true conditions on the ground.

“We have to understand that the AQHI was not originally designed to reflect the risks associated with wildfires. It was designed to reflect the risks associated with urban air pollution,” said Sarah Henderson, scientific director of Environmental Health Services at the British Columbia Centre for Disease Control.

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

“Wildfire smoke is a totally different ballgame,” Henderson explains.

Plumes of wildfire smoke arrive and dissipate unpredictably, creating 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 the AQHI relies on, which can suddenly skyrocket as the other two stay flat — just as Toronto saw on Wednesday afternoon.

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

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

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

B.C.’s AQHI now calculates two scores at the same time: the three-hour average of the three major pollutants, the mix usually found during an urban smog day; and the one-hour average of fine particulate matter alone, which better reflects wildfire smoke. Whichever results in the higher AQHI score is the one the public sees.

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

“Some of the smaller provinces that have less policies to go through to to implement the new formula, they were able to implement it right away. We’re still working with some of the other partners, and they’re working with their senior management to implement it in their jurisdictions.”

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

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

Alberta already uses an enhanced air quality index that overrides the mixed-pollutant result when single value spikes up, but uses a different formula; the province is considering switching to the federal system, a spokesperson said. Quebec uses a different system that reports PM2.5 directly.

Audette urged Canadians to continue to pay attention to the AQHI, but also to look out for Special Air Quality statements, which are issued by Environment Canada directly: “once there’s a special air quality statement, that is your confirmation that there’s an actual problem.

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