Smog settles over downtown Montreal this week. (CBC) Montrealers lighting up their wood stoves to fight off the chill of an exceptionally cold winter have led the city to set a record for winter smog.

The city has recorded 21 smog days since November — the highest number since Environment Canada started recording smog days in 2004.

On Tuesday evening, Environment Canada recorded the city's air quality index at 108, compared to the acceptable limit of 50.

Radio-Canada meteorologist Pascal Yiacouvakis said the cold air masses that have settled over Quebec in the past month have created favourable conditions for winter smog.

The temperature has been 3.2 C colder this January compared to the average, he said.

As the cold air sits close to the ground and the warm air rises to the higher levels of the atmosphere, there is little air circulation, he said. As a result, pollutants get trapped.

Add that to the increased use of wood-burning stoves, and smog is a certainty, Yiacouvakis said.

"Wood burning — this is the main cause because people are using this type of heating when temperatures are low. So, all of the conditions are met," he said.

He expects more smog days this winter. The previous record was set in 2005 when Montreal recorded 19 smog days for the entire winter period.

Environment Canada estimates that 47 per cent of the fine particulate matter in Quebec's air comes from fireplaces and wood stoves.

Cities, province want to turn down the heat on wood stove use

Many Quebecers have installed wood stoves in their homes over the past few years. For some, it has been a way to save money on home heating costs.

For others who still have strong memories of the Quebec ice storm of 1998 that cut power to millions of homes for many days, the wood stove is considered a good back-up source of heat.

But as winter smog becomes a bigger problem in the province, some municipalities are passing bylaws to restrict the use of wood stoves.

Already, the Quebec municipality of Hampstead has ordered its residents to get rid of their wood stoves or convert them to gas models by 2015.

People who want to build new homes in the Montreal boroughs of Ville St-Laurent and St-Léonard are barred from installing wood-burning devices.

The City of Montreal is considering its own set of regulations.

The Quebec government is also preparing legislation that would impose new environmental norms on the sales of wood stoves.

The new law, if adopted, would make it illegal to sell a wood stove in the province that does not meet standards set by the Canadian Standards Association or the U.S. Environmental Protection Agency. Violations of the proposed law could result in fines of up to $25,000.