In 2005, smog hung over Toronto for 48 days during what was then one of the warmest summers on record, with 38 days when the temperature soared to 30C or above. Six people died due to the heat, humidity and air pollution.

It was the worst year for smog — a record — but only one of many from 2003 to 2013, a period when the city had so many smog days they added up to nearly half a year, according to air quality data obtained by the Star from Ontario’s environment ministry.

Since 2014 — the year the Ontario government shuttered the last of the province’s coal-fired electricity plants — Toronto has had only one.

But does it mean that smog days are gone for good?

No, says Yushan Su, a senior scientific adviser with the environment ministry’s air quality monitoring unit. Only that they are less likely.

Coal was cleaned up at a time when our air quality was improving due to a number of changes, which makes it difficult to quantify just how much the coal plants contributed to our smog.

Pollution decreased due to Drive Clean, the province’s vehicle emissions testing program, as well as reductions in industrial emissions both here and in the United States, says Su.

But it is known that the plant closures eliminated 150,000 tonnes of sulphur dioxide and nitrogen oxides, which contribute to smog, according to a spokesperson for the provincial ministry of the environment, conservation and parks.

The plant closures also prevented 30 megatonnes of annual greenhouse gas emissions — the equivalent to taking seven million cars off the road.

“It’s the biggest thing that’s been done in this country on climate change. It really was huge,” says Kim Perrotta, senior director of climate and policy for the Canadian Association of Physicians for the Environment.

Perrotta worked in the early 2000s on air quality issues for Toronto Public Health, one of the many organizations working alongside the Ontario Clean Air Alliance, which led the campaign to phase out coal.

Then, the air pollution was termed a “public health crisis” by the Ontario Medical Association, which called for massive reductions in emissions such as nitrogen oxides, which are a precursor to ground level ozone, a major component of smog.

Ground level ozone can cause coughing, irritation of the eyes or nose, shortness of breath and decreased lung function.

The plants included the Lakeview Generating Station in Mississauga, which ceased operation in 2005, followed by Atikokan, northwest of Thunder Bay, which closed in 2012. Nanticoke, near Port Dover, and Lambton, on the St. Clair River south of Sarnia, were shut down in 2013. The last closure was Thunder Bay’s coal-fired plant in 2014.

Until then, Ontario relied in part on coal-fired electricity generation and it was the first jurisdiction in the world to phase it out, according to the Ontario Clean Air Alliance.

But Perrotta says after the plants closed, people stopped talking about air pollution. They thought the problem was solved, she says.

“One of the things I’d like to point out is that air pollution, even though much improved, is still a significant health concern in Ontario. And it’s just been hard to turn people’s attention to it,” says Perrotta.

Data from Health Canada in 2018 says 14,400 deaths annually are attributable to air pollution.

“And the big source of pollution in Southern Ontario is transportation-related air pollution,” says Perrotta.

Major improvements, though, could be realized if Premier Doug Ford’s government brings in stricter emission standards for heavy-duty diesel vehicles, standards the government promised last fall when the premier announced the end of Drive Clean.

“Our new, enhanced and redesigned emissions testing program will focus on improving emissions testing on heavy-duty diesel vehicles like commercial transport trucks and will take action to prevent tampering and fraud with emissions control systems,” says Gary Wheeler, a spokesperson with the ministry of environment, conservation and parks.

If implemented, the changes might have a similar impact on air pollution — and therefore human health — as the phaseout of coal.

Diesel exhaust is a recognized carcinogen, according to the International Agency for Research on Cancer, which is part of the World Health Organization.

The tiny particles that are emitted in the exhaust can get deep into the lungs, and even the blood stream, causing heart attacks, heart failure and arrhythmias, as well as stroke and blood clotting, according to Chris Carlsten, a professor of medicine and head of respiratory medicine at the University of British Columbia. Carlsten is also director of the university’s Air Pollution Exposure Laboratory.

The provincial government is reviewing the current emission standards in Ontario, which allow for the density of the smoke emitted by heavy-duty diesel vehicles to be 30 or 40 per cent, depending on the year of manufacture.

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Carlsten says there are known health hazards even when there is no visible smoke.

Heavy-duty trucks also contribute more than half of nitrogen oxides (NOx) emissions from all vehicles in the province, according to 2014 data from Environment Canada. Yet, the trucks represent less than 2 per cent of vehicles on the road, based on 2009 figures from Natural Resources Canada.

NOx is a major contributor to the ozone that can form in hot sunny weather.

The problem isn’t unique to Ontario.

In California, where diesel emissions from trucks contribute nearly a third of all NOx emissions in the state, including those from transportation, industry and other sources, a state senator has proposed a bill that would prohibit visible exhaust from heavy-duty vehicles as well as increase enforcement to ensure drivers are repairing emission controls.

Roadside testing in the state has already led to the recall of 500,000 heavy-duty trucks operated by one firm after NOx emissions were found to have exceeded federal and state levels because of a defective selective catalytic reduction, technology which is supposed to lower emissions.

“Emissions testing programs are ultimately what caught Volkswagen in their massive scandal,” says Suzanne Paulson, a professor in UCLA’s department of atmospheric and oceanic studies and director of the Center for Clean Air. Volkswagen was caught by independent testing. “The thing is if we don’t test them, we don’t really know what’s going on.”

The pollutants are becoming more of an issue in California, where bad air days are on the rise after years of improvement.

Scientists believe climate change is a factor.

Higher temperatures accelerate the chemical reactions that create ground level ozone, allowing it to concentrate more quickly, says Paulson.

And “climate change kind of intensifies the formation of a warm air layer higher up,” she says, trapping the pollution in the cooler layer below.

Ontario hasn’t seen a resurgence of smog, but ozone concentrations have stayed stubbornly unchanged and scientists say it could be related to climate change, according to a 2014 report from Toronto Public Health.

Perrotta, of the Canadian Association of Physicians for the Environment, says climate change may still be too large and abstract a concept for people to act on.

“We find that when we talk more about solutions that produce immediate air pollution health benefits, (people) can see that their child or their grandmother is going to benefit from that,” says Perrotta. “Whereas I think with climate change, they think that if everybody doesn’t do it — if we don’t reduce greenhouse gases globally — then it’s not going to have any effect so why should I sacrifice too much for it.”

A recent poll by the Public Policy Forum’s Digital Democracy Project seems to back that up.

The poll found that although a majority of Canadians support reducing emissions, and policies such as renewable energy subsidies or increased regulations to cut down on pollution, there was less appetite to pay more at the pumps in carbon taxes, which are a reminder to drivers that burning fossil fuels is a major contributor to climate change. The tax, already factored into gasoline prices at about 4 cents a litre, could become a divisive federal election issue.

Perrotta’s organization focuses on issues such as public transit, electrifying rail service and cycling.

“These are all things that would have a huge, immediate benefit for human health by reducing air pollution, while at the same time they would really help to reduce greenhouse gases that contribute to climate change,” says Perrotta.

“For me as a public health professional, I see climate change as the most significant public health challenge of this century.”