The union representing subway workers in Toronto is considering legal action over newly published research that suggests levels of pollution in the underground stations are up to 10 times worse than the air outside.

Air quality on the Toronto Transit Commission’s subway system is comparable to a typical day in Beijing, said study co-author Greg Evans, an engineering professor at the University of Toronto.

The study, published this week, determined that Toronto’s subway had three times more air pollutants than Montreal’s subway system, and five times more than Vancouver’s SkyTrain system.

The TTC said it has made improvements in its HVAC system and has commissioned new subway cars since the researchers collected airborne particulate matter from platforms and trains over three weeks in the summer of 2010 and winter of 2011.

The amount of particulate pollutants outdoors in Toronto on a typical day is pegged at around 10 micrograms of fine particulate matter per cubic metre. But researchers found that on Toronto subway platforms and trains air quality was measured at an average of 100 micrograms per cubic metre.

The study’s authors say TTC’s million daily riders should not be alarmed by the findings but they should be aware. Evans says if you take the subway an hour a day, you’re taking in about 20 per cent of your daily average exposure to fine particulate matter, which has been linked to respiratory problems.

"If you take an average day of air quality in Beijing, which are both the good days and the bad days, the Toronto subway system has air quality similar to that," said Evans. An average daily reading of airborne pollutants in the Chinese capital is seven times above what the World Health Organization considers safe.

The last time air quality in the subway system was studied was in 1995. That is unacceptable, says Kevin Morton, secretary-treasurer of ATU Local 113, Toronto Transit Workers. He says the union is demanding an immediate investigation by provincial health, environment and labour ministries, along with the WSIB. It's also pondering taking legal action.

“How can you go for 22 years and not do a study on the air quality in the subway system, but you can improve the air conditioning for the public? But you can't improve the ventilation system for the workers? This is criminal, just criminal."

Those working at businesses in the subway system, like convenience stores and food kiosks, say they are concerned.

“Just because of black dust. The air pollution is too high,” said a man working at one store. He said he worries sometimes about working there.

Another man at a different kiosk said he can feel the pollution in his lungs. When asked if he worries, he said: “What can I do? No choice. We cannot have the doors closed, we cannot stop the train. Worried about it, but we don't have a choice to stop.”

Subway riders also expressed worry, though one man said he wasn’t surprised by the findings.

“It does concern me because I know pollution levels on street level are not so good itself,” said another subway rider.

The TTC says it has undertaken system improvements since the data was collected.

"This research was done in 2010 and 2011 at a time we had already started taking steps that will improve air quality on the trains and reduce certain pollutants in the underground stations,” said spokesperson Stuart Green in a statement.

The TTC added that it’s improving and refurbishing heating, ventilation and air-conditioning systems and looking into purchasing a tunnel vacuum car with a hepa-filtration system.

Toronto city councillor and TTC board member Joe Mihevc told CTV News Channel on Tuesday that it’s important to get updated data, and to understand the impact of fine particulate pollution on public health for passengers waiting on platforms, riding in cars, and for the workers in the subway.

He said the findings may be another reason, beyond suicide prevention, to look at the platform-edge doors that are used in some Asian cities that would “segregate the subway car from the passengers as they waiting on the platforms.”

Mihevc, who also chairs the Toronto board of health, said he will push to have the issue referred to public health staff for their recommendations for immediate and long-term mitigation strategies.

He said he’s not concerned about a class-action suit because “I think any court would find the TTC is doing the best that it can to mitigate any risk.”

In an interview with CTV News Channel Tuesday, Evans said three things are happening on a subway platform in Toronto when higher levels of pollutants are detected.

As the train comes into the station it pushes air into the tunnel, stirring up existing particles. “It’s like a piston, and it pushes a lot of the air in front of it.”

When the train brakes, abrasion between the wheels and the train track create tiny steel particle pollutants. And, when the train doors open, the particles are pushed into the subway car, along with the passengers.

Vancouver’s Skytrain system is mostly above ground, explaining why its air quality index was superior.

And Evans said Montreal’s higher air quality reading could be attributed to the fact they use rubber wheels, concrete rails and wood-based braking system, while Toronto’s is steel-on-steel.

Evans said that the findings of the study present an opportunity to take “positive steps that can be of benefit to a large number of Torontonians.”

To reduce the amount of pollutants, TTC officials should re-examine how the trains are driven, sweep tunnels and remove particle concentration with better filtration systems, Evans said.

“There are a number of positive things that can be done and I’m hopeful that the TTC is going to very proactive and is going to undertake these steps,” he said.

The study is published in the journal Environmental Science and Technology.

With a report from CTV News Toronto