Smog clouds Montrealers' commute

Montrealers made their way to work Thursday amid smog for the third day in a week.

Montrealers made their way to work Thursday amid smog for the third day in a week.

It is a situation that is uncommon in the fall, but not unheard of, said Environment Canada meteorologist René Héroux.

"The winds are really light ,so the air is stagnant, so all the pollution after a few days it just builds up," Héroux said.

While smog in the summer is generally caused by levels of ozone in the air, fall smog is different, Héroux said.

"Any burning from the fuel of vehicles or the industry, it's never a complete burning, there's always very, very small particles and that's [this] type of smog," said Heroux.

Montrealer Tricia Foster said she was confused to see the thick air when she awoke.

"I thought there was like a lot of fires," she said. "It just stunk and it was hard on the lungs."

Children are among those most affected by poor air quality, said epidemiologist Norman King from the Montreal Public Health Department.

"They … breathe more air per unit of body weight than adults, so in a way they’re more exposed," said King. "The very young, the very old and the chronically ill are the people we're most concerned about."

The smog is expected to clear Friday thanks to the arrival of wind and rain, Héroux said.