About Smog Advisories

What is the purpose of smog watch and smog advisory?

The main purpose of these alerts are to warn people with breathing difficulties to avoid unnecessary exposure to smog and to provide advice to the public on actions they can take to reduce activities that contribute to smog.

What is a smog watch?

The Ministry of the Environment issues a smog watch when there is at least a 50 % probability that smog conditions will occur within the next three days.

What is a smog advisory?

The Ministry of the Environment issues a smog advisory when there is a high probability of a smog day occurring within the next 24 hours. A Smog Advisory would be issued immediately if a smog day has occurred without warning and weather conditions conducive to elevated smog are forecast to continue for six hours.

What are the health effects of smog?

What should I do if a smog alert is issued?

Here are some actions you can take to help protect the environment and your own health:

At home:

At work:

As always, consult your doctor for specific medical advice on how to cope with poor air quality.

Where does Ontario's smog originate?

Ontario's smog problem is generally observed on hot, sunny days from May to September. Local sources of pollution and pollution from the United States can add significant amounts of ozone and ozone-forming compounds into the air that contribute to elevated smog concentrations. During periods of widespread elevated ozone, it is estimated that more than 50% of Ontario's ground-level ozone can be attributed to trans-boundary pollution.

The map below shows the area from which southern Ontario air originates during days of widespread elevated ozone levels.

Map showing the area from which southern Ontario air originates during days of widespread elevated ozone levels