Ministère de l'Environnement
et de la Lutte contre les changements climatiques


What is smog?

Smog is a yellowish haze caused by the accumulation of a mixture of atmospheric contaminants that limits visibility in the atmosphere. It is primarily composed of fine particulate matter and ozone. It can occur at any time of the year. In summer it is mostly made up of ozone (O3) and fine particulate matter (PM2.5). However, in winter it is mainly characterized by fine particulate matter.

Smog over Québec City
Summer smog Good air quality Winter smog
Vue du 31e étage de l'Édifice Marie-Guyart vers l'est - Photo Roger Lemire MDDEP Vue du 31e étage de l'Édifice Marie-Guyart vers l'est - Photo Roger Lemire MDDEP Du 29e étage de l’édifice Marie-Guyart à Québec - Photo : Manon Therrien, MDDEP
September 10, 2002 - 3:32 p.m.
PM2,5 concentration = 45 µg/m³
O3 concentration = 90 ppb
September 24, 2002 - 3:45 p.m.
PM2,5 concentration = 1 µg/m³
O3 concentration = 24 ppb
February 2, 2002 - 9:00 a.m.
PM2,5 concentration = 53 µg/m³
O3 concentration = 5 ppb

Smog-causing contaminants originate from local and cross-border emission sources. Winds carry fine particulate matter, ozone and their precursor pollutants to Québec from southern Ontario and the central United States. The farther one gets from the Great Lakes region, the more the sources are attributable to Québec emissions.

Smog can affect the health of the most vulnerable population groups any time of the year. These include young children, the elderly and people with respiratory or heart problems. Find out more about the origin and impacts of air contaminants.

For more details

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