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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?

  • Smog can cause health problems for all people especially the elderly, those who suffer from respiratory and cardiac problems and children because they breathe faster and spend more active time outdoors. Even healthy young adults breathe less efficiently on days when the air is heavily polluted.
  • As people spend more time outdoors in the spring and summer months exposure to smog increases. You are more likely to experience adverse health effects with an increase in the amount of smog you breathe in.
  • Sensitive people may experience symptoms after only one or two hours outdoors.
  • Studies have shown that smog can lead to premature death, increased hospital admissions, more emergency room visits and higher rates of absenteeism
  • Ground-level ozone, a major component of smog, affects the body's respiratory system and causes inflammation of the airways that can continue several hours after exposure. Ground-level ozone can cause coughing, wheezing and chest tightness. In addition, existing heart and lung conditions may be aggravated. Evidence also indicates that exposure to ground-level ozone heightens the sensitivity of asthmatics to allergens.
  • Small airborne particles known as particulate matter is the other major component of smog that can also create adverse health effects. Very fine particles can penetrate deep into the lungs and interfere with the functioning of the respiratory system. These fine particles have been linked to increases in asthma symptoms, hospital admissions and even premature mortality. Typically, those who are sensitive to ground-level ozone are also sensitive to airborne particles.

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:

  • Conserve electricity year-round by adjusting the heat or air conditioner and turning off lights you are not using.
  • Avoid letting your car, or any other engine, idle for long periods.
  • Reduce your use of gasoline-powered equipment.
  • Avoid mowing the lawn when air quality is poor.
  • Don't use oil-based products such as paints, solvents or cleaners if you can avoid them. They contain volatile organic compounds (VOCs), which contribute to smog.
  • Get engine tune-ups and car maintenance checks as advised by the car manufacturer's maintenance schedule.
  • Limit the amount of wood you burn in your fireplace or woodstove. When burning wood, use only the dry, seasoned variety.
  • Avoid or reduce strenuous physical outdoor activities when smog levels are high, especially during the late afternoon. Do not exert yourself outdoors
  • If possible, stay indoors in a cool, air-conditioned environment

At work:

  • If possible, take public transit, or walk to work.
  • If you use a car, don't travel alone; encourage and facilitate car pooling.
  • Avoid traffic congestion.
  • Consider teleconferencing, instead of traveling to meetings.

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