Ozone is a gas comprised of three oxygen (O3) atoms. It is unstable and reacts easily to other gases. In its natural state, it is a component in several levels of the atmosphere. At high altitudes ...

Smoke from wildfires in northern Quebec in Canada covered the city of Montreal in smog on Sunday. It led to the city’s air becoming the world’s most polluted, according to an air quality index.

With Montreal, Que., seeing its warmest fall on record, it makes sense it has yet to see any accumulating snow. But that is about to change this week with an inbound Alberta clipper. Shots of ...