Urban air pollution is made up of a complex mix of hundreds of substances including toxic air pollutants and criteria air contaminants such as nitrogen oxides (NOx), sulphur oxides (SOx), and particulate matter (PM).

What is smog?

Sometimes people talk about “smog”, a mixture of pollutants in the air that can affect our health. Smog can occur any time of year, but it is most common in the summer. It sometimes appears as a brownish haze. Smog is made up of ground-level ozone, fine particles and other pollutants. Smog can affect outlying suburbs and rural areas as well as big cities.

Where does smog come from?

The air pollutants that make up smog mainly come from burning fossil fuels. Every day we burn gasoline, diesel fuel, natural gas and coal in our cars, trucks, home furnaces, industries and power plants, we are sending pollutants into the air. Ozone, the main ingredient in smog, is formed when two pollutants (nitrogen oxides and volatile organic compounds) combine in the presence of sun light. Toronto’s smog comes from sources in Toronto and beyond.