As the colder weather sets in across southern Quebec, wood heating is being blamed for a smog warning in the Greater Montreal area and parts of the Laurentians, Montérégie, Lanaudière, Mauricie and Quebec City regions.

Environment Canada issued the warning Sunday evening and says people with respiratory problems, such as asthma, should avoid intense physical activity for the time being.

"High concentrations of fine particulates are expected and will result in poor air quality," the warning says. 

Wood heating is the main source of those fine particles that contribute to smog in the winter — more even than industrial activities and transportation, according to Environment Canada.

"Montreal residents — stop using your wood-burning stove or fireplace until the smog warning has been lifted," the warning reads. Under a municipal bylaw, owners of solid fuel-burning appliances aren't allowed to use them while smog warnings are in effect.

The weather agency says everyone can contribute to improving air quality by limiting the use of fireplaces and wood-burning stoves, opting to use public transit, reducing driving speed and not letting car engines idle unnecessarily, for example.