If Montrealers are breathing easier of late, there's a reason: air quality in the city is the best it's been in more than a decade.

The lower levels of smog and air pollution, however, aren't entirely because of changes made locally.

Environmental advocates say the improvements are mostly due to the shuttering of Ontario's coal-fired power plants.

According to data compiled by Radio-Canada, 2016 was the best year in terms of air quality since 2002.

The number of days in Montreal where air quality was considered "poor" and dangerous to public health also dropped by about 60 per cent in one year.

In 2016, a total of 26 days with bad air quality was recorded in Montreal, which is a sharp contrast compared to 64 in 2015.

Smog days in the city are also on the decline. In total, there were only five days with smog warnings in 2016 and they were all in the winter.

Still room for improvement

The Association québécoise de lutte contre la pollution atmosphérique, a provincial environmental group, says the main reason for the decline in air pollution is the closure of five coal-fired power plants in Ontario.

"It has a direct and measurable impact," said president André Bélisle.

Bélisle says that while more can be done to reduce pollution such as cracking down on wood-burning stoves, that better air quality is here to stay due to the closure of the Ontario plants and the Shell refinery in Montreal's east end in 2014.

"It's major, because these plants were a heavy burden on the atmosphere," said Bélisle.

The closure of several coal-fired power plants in the American Midwest were also a factor, he said.

Smog warnings in Montreal are also on the decline. (Paul Chiasson/The Canadian Press)

François Reeves, a cardiologist and professor at the Université de Montréal, told Radio-Canada that only 40 per cent of the city's air pollution is generated locally.

Ontario and the United States are the source of 60 per cent of Montreal's air pollution.

However, Reeves said that there is still room for improvement. The data shows that number of days where Montreal's air quality was given a grade of "acceptable" didn't change from 2015 to 2016.

He adds that poor air quality poses health risks to Montrealers suffering from chronic illnesses such as heart and long-term pulmonary diseases.

Montreal's public health agency reports that 1,500 people die annually from poor air quality in the city.​