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Air Quality

Smokey outdoor air

The air around us is made up of nitrogen (78%), oxygen (21%) and tiny amounts of other gases. Both natural and human activities release gases that cause an imbalance in the air. These releases of gases are called air pollutants.

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Types of Pollutants

Carbon Monoxide (CO) is a colourlessodourless, and tasteless gas. It is a by-product of incomplete combustion of fossil fuels. In Ontario, the main sources of CO emissions come from road vehicles and other forms of transportation. When CO is inhaled, it enters the blood stream and reduces our bloods ability to carry oxygen to our tissues and organs. Exposure to high levels of CO has been associated with impaired vision, headache, dizziness, weakness, confusion and may also lead to death.

Carbon monoxide poisoning — Government of Canada

Hydrogen sulfide (also known as H2S, sewer gas, swamp gas, stink damp, and sour damp) is a colorless gas known for its pungent "rotten egg" odor at low concentrations. It is extremely flammable and highly toxic.

Hydrogen sulfide is used or produced in a number of industries, such as

  • Oil and gas refining
  • Mining
  • Tanning
  • Pulp and paper processing
  • Rayon manufacturing

Hydrogen sulfide also occurs naturally in sewers, manure pits, well water, oil and gas wells, and volcanoes. Because it is heavier than air, hydrogen sulfide can collect in low-lying and enclosed spaces, such as manholes, sewers, and underground telephone vaults. Its presence makes work in confined spaces potentially very dangerous.

What is Hydrogen Sulfide?

What is smog?

The word smog was first used to describe a mixture of smoke and fog in the air. The word smog now refers to a brownish-yellow hazy cloud made up of harmful pollutants, including gases and fine particulates. Although smog usually starts in larger cities, it can be just as prevalent or more prevalent in rural and suburban areas.

A Smog Advisory means that there is a strong likelihood that there may be poor air quality within the next 24 hours due to ground-level ozone and/or particulate matter.

  • During the smog episode, individuals may experience eye irritation.
  • Heavy outdoor exercise may cause respiratory symptoms such as coughing or shortness of breath.
  • People with heart or lung disease including asthma may experience a worsening of their condition.

When is smog a problem?

Smog is usually a problem in Ontario between May and September. It is important to remember, however, that smog is a year-round problem and does occur outside of the summer months.

What creates smog?

  • Gas-powered and diesel-powered vehicles.
  • Homes.
  • Industries.
  • Coal-fired power plants.
  • Pesticides and herbicides.
  • Oil-based paints, solvents and cleaners.
  • Wood-burning fireplaces.
  • Road paving and construction.
  • Barbecues.
  • Gas-powered and diesel-powered lawn mowers.
  • Natural occurrences such as forest fires and plant growth.

It is estimated that 50% of Ontario’s air pollution is blown over from sources in the United States.

Health Effects of Smog

  • Eye, nose, and throat irritation.
  • Irritate existing heart and lung problems.
  • In rare cases may result in death.

People with existing lung and heart problems are most at risk. Since these problems are more common with seniors, they are more likely to experience the negative effects of air pollution. Children can also suffer from the effects of air pollution since their respiratory system is still developing and they tend to have an active lifestyle.

The impact of air pollutants on your heath will depend on a number of factors, including where you live, your age and stage of health, the influence of weather, and how long you have been exposed.

How to Help Reduce Smog

  • Take public transportation, walk, ride your bike (as long as smog levels are not too high).
  • Use alternatives to gas-powered machines.
  • When purchasing a new vehicle, consider fuel efficiency.
  • Reduce energy in your home.
  • Do not burn leaves, branches or yard waste.
  • Talk to your children about the importance of reducing air pollution.

Minimizing Smog Risk

  • Check the Air Quality Index in your community.
  • Avoid or reduce strenuous activity during times when smog levels are high.
  • Avoid exercise near highway areas during peak hours when levels of traffic are higher.
  • If you have a heart or lung condition, talk to your doctor about ways to protect your health when smog levels are high.

Types and Sources of Air Pollution

  • Type: Particulate Matter (or PM). This is the name given to microscopic particles that pollute the air. They vary in size and chemical make-up. 
    Sources: Industrial and vehicle emissions, road dust, agriculture, construction and wood burning.
  • Type: Ground-level ozone. This gas results from a chemical reaction when certain pollutants are combined in the presence of sunlight. Ground-level ozone shouldn't be confused with the ozone layer in the sky, which protects us from ultraviolet radiation.
  • Sources: Ground-level ozone comes mostly from burning fossil fuels for transportation and industry. Ozone levels peak between noon and 6 p.m. during the summer months.

Additional Air Quality Concerns

  • Sulphur dioxide – from coal-fired power plants and non-iron-ore smelters.
  • Carbon monoxide – mostly from burning carbon fuels (e.g., motor vehicle exhaust).

The Air Quality Index

The Air Quality Index (AQI) is a provincial air quality monitoring and information system.


0-15 Very Good
16-31 Good
32-49 Moderate
50-99 Poor
100+ Very Poor

Spare the Air Actions

During a smog advisory, there are a number of actions that you can take to help spare the air.

Travel tips - all year round:

During the smog episode, individuals may experience eye irritation.

  • Leave your car at home - walk, cycle, carpool or take public transit.
  • Tele-conference instead of driving to meetings.
  • Limit car trips by doing all your errands at once, and do not let your engine idle.
  • Keep your car well tuned, check your tire pressure and drive at moderate speeds.

Electricity saving tips:

  • Save electricity at home by setting your air conditioner temperature a few degrees higher (health permitting) and turning off lights you are not using.

For more information see Today's Smog Advisory.

Health Effects

Short term exposure to high levels of certain air pollutants may lead to:

  • Irritation of the eyes, nose, and throat
  • Wheezing, coughing, chest tightness, and difficulty breathing
  • Worsening of existing lung and heart problems, such as asthma
  • Increased risk of heart attack

Long-term exposure to air pollution can cause cancer and damage to the immune, neurological, reproductive, and respiratory systems.

While air pollution can affect everyone’s health, infants, children, older adults and people with existing breathing or heart problems are more vulnerable to the effects.

If you experience health effects as a result of exposure to outdoor air pollutant, seek the advice of your primary health care provider.


What is the Air Quality Health Index?

The Air Quality Health Index (AQHI) is a scale designed to help you understand what the air quality around you means to your health. This can help you make decisions to protect your health by limiting short-term exposure to air pollution.

Learn more about the Air Quality Health Index and what to do during high-risk events.