Generally, air quality improves as you travel northward and eastward across the province, however, the formation and transport of smog is strongly dependent on meteorological conditions.

Summer smog episodes in Ontario are often a part of a regional weather condition that prevails over much of northeastern North America. Elevated levels of ozone and fine particulate matter are typically due to weather patterns that affect the lower Great Lakes region. Such weather patterns are invariably associated with slow-moving high pressure cells across the region and result in the long-range transport of smog pollutants from neighbouring U.S. industrial and urbanized states during the flow of warm air from the southwest to the northeast.

When looking for a place to live, it is important to keep local sources in mind. For instance, it is best to stay away from areas with a lot of industry and major roadways. The impacts of emissions from vehicles on a highway or any roadway depend on a number of factors, including: the distance from the highway; traffic volume; traffic congestion (i.e. free flowing or congested); and predominant wind directions.

Generally speaking, air concentration impacts from a highway decrease significantly with distance from the roadway. Typically, moving 100 metres from the edge of the road can result in a decrease in pollutant concentrations of 60-80 per cent. In addition, trees can filter the air, so a well-treed area can have better air quality than one without trees.

The contaminants that create smog are released during the combustion of fossil fuels in our vehicles, power plants, factory boilers and homes. They are also released by industrial processes, the evaporation of liquid fuels and the use of solvents and other volatile products such as oil-based paints. Smog-causing contaminants are released during forest fires, and emitted by natural sources such as trees, bogs, and volcanic activity. Most of Ontario's smog problems are caused by a combination of local emissions and pollutants carried by the wind from pollution sources in the United States. More than half of our smog problem comes from south of the border.

The Ontario Ministry of the Environment, Conservation and Parks and Environment and Climate Change Canada want to give Ontario residents the best tools to make decisions to protect their health by limiting short-term exposure to air pollution and adjusting their activity levels during increased levels of air pollution.

The Air Quality Health Index (AQHI), implemented in June 2015, replaced the old Air Quality Index. The AQHI is a health protection tool that is designed to help you make decisions to protect your health by limiting short-term exposure to air pollution and adjusting your activity levels during increased levels of air pollution. It also provides advice on how you can improve the quality of the air you breathe.

This index pays particular attention to people who are sensitive to air pollution and provides them with advice on how to protect their health during air quality levels associated with low, moderate, high and very high health risks.

The AQHI communicates four primary things:

1. Measures the air quality in relation to your health on a scale from 1 to 10. The higher the number, the greater the health risk associated with the air quality. When the amount of air pollution is very high, the number will be reported as 10+.
2. Assigns a category that describes the level of health risk associated with the index reading (e.g. low, moderate, high, or very high health risk).
3. Provides health messages customized to each category for both the general population and the ‘at risk’ population.
4. Shows current hourly AQHI readings and maximum forecast values for today, tonight and tomorrow.

The AQHI is designed to give you this information along with some suggestions on how you might adjust your activity levels depending on your individual health risk from air pollution.

The AQHI is based on the cumulative health effects of three common air pollutants: ozone, nitrogen dioxide, and fine particulate matter. In Ontario, if the following pollutant thresholds are exceeded when the Air Quality Health Index is low or moderate risk (6 or less), then the AQHI is replaced with the appropriate high or very high risk value (7 or greater):

• 80 parts per billion for ozone
• 60 micrograms per cubic metre for fine particulate matter*
• 200 parts per billion for nitrogen dioxide

*In addition, PM_2.5 can override the AQHI at any time when health risks associated with PM_2.5 are greater than the AQHI. The AQHI is then calculated and reported using only the hourly PM_2.5 concentration.

The Air Quality Health Index provides a number on a scale from 1 to 10+ to indicate the level of health risk associated with regional air quality in your area. Occasionally, when the amount of air pollution is abnormally-high, the number may exceed 10.

The higher the number, the greater the health risk and our need to take precautions.

Air Quality Health Index Categories, Values and Associated Colours

Air Quality Health Index Categories and Values
1	2	3	4	5	6	7	8	9	10	+
Low Risk (1 - 3)			Moderate Risk (4 - 6)			High Risk (7 - 10)				Very High Risk

The table below provides the health messages for each category of the Air Quality Health Index for the "at risk" population and the general population.

Health Risk	Air Quality Health Index	Health Messages
		At Risk Population*	General Population
Low	1 - 3	Enjoy your usual outdoor activities.	Ideal air quality for outdoor activities.
Moderate	4 - 6	Consider reducing or rescheduling strenuous activities outdoors if you are experiencing symptoms.	No need to modify your usual outdoor activities unless you experience symptoms such as coughing and throat irritation.
High	7 - 10	Reduce or reschedule strenuous activities outdoors. Children and the elderly should also take it easy.	Consider reducing or rescheduling strenuous activities outdoors if you experience symptoms such as coughing and throat irritation.
Very High	Above 10	Avoid strenuous activities outdoors. Children and the elderly should also avoid outdoor physical exertion.	Reduce or reschedule strenuous activities outdoors, especially if you experience symptoms such as coughing and throat irritation.

* People with heart or breathing problems are at greater risk. Follow your doctor's usual advice about exercising and managing your condition.

Ontario’s air monitoring network is comprised of stations that are generally representative of regional air quality which are less influenced by local and industrial sources of air contaminants in urban and rural areas. The surrounding air monitoring site(s) closest to your location may be used to determine the air quality in your area.

The purpose of these alerts is to advise people with breathing difficulties to avoid unnecessary exposure to smog. They also inform industries that are major sources of pollution to consider, if possible, reducing their emissions. Additionally, they solicit everyone's help in lessening the problem by curtailing activities that produce smog.

A SAQS will be issued when the Air Quality Health Index is forecast to reach the high risk category (an AQHI of 7 or greater).

An AQA will be issued when the AQHI is forecast to reach, or has reached, the very high risk category (AQHI of 10+) due to wildfire smoke.

Both are issued jointly by the Ontario Ministry of the Environment, Conservation and Parks, and Environment and Climate Change Canada.

Yes. Since smog is closely tied to the weather, it is impossible to be 100 per cent accurate 100 per cent of the time. For example, a weather system could arrive in Ontario before the predicted time or could change direction.

High risk Air Quality Health Index values could occur without an air quality alert being issued. It is also possible that high risk Air Quality Health Index will not materialize even though an air quality alert has been issued.

Yes! The air quality alert email system is a notification service that provides advanced warning of a Special Air Quality Statement or Smog and Air Quality Advisory.

By subscribing to the service, there are three kinds of notifications that you can expect to receive by email.

• Special Air Quality Statement (SAQS): A SAQS will be issued when the AQHI is forecast to reach the high risk category (AQHI of 7 or greater).
• Air Quality Advisory (AQA): An AQA will be issued when the AQHI is forecast to reach, or has reached, the very high risk category (AQHI of 10+) due to wildfire smoke.
• Termination Notice: A termination notice is issued once the air quality alert has ended.

Both Special Air Quality Statements and Air Quality Advisories are issued jointly by the Ontario Ministry of the Environment, Conservation and Parks, and Environment and Climate Change Canada.

Air quality alert notification is provided all year round with the majority of alerts being issued during the May to September period depending on the weather conditions.

• Sign up to receive Air Quality Alert Email Notifications
• Update your subscription to the Air Quality Alert Email Notifications
• Cancel your subscription to the Air Quality Alert Email Notifications

Depending on the length of time you are exposed, your health status, your genetic background and the concentration of pollutants, air pollution can have a negative effect on your heart and lungs. It can:

• Make it harder to breathe
• Irritate your lungs and airways
• Worsen chronic diseases such as heart disease, chronic bronchitis, emphysema and asthma

Each person reacts differently to air pollution.

Seniors are at higher risk because of weakening of the heart, lungs and immune system and increased likelihood of health problems such as heart and lung disease.

Children are also more vulnerable to air pollution; they have less-developed respiratory and defense systems. Children also spend more time outdoors being physically active, which can increase their exposure to air pollution.

People participating in sports or strenuous work outdoors breathe more deeply and rapidly, allowing more air pollution to enter their lungs. They may experience symptoms like eye, nose or throat irritation, cough or difficulty breathing when air pollution levels are high.

Negative health effects increase as air pollution worsens. Small increases in air pollution over a short period of time can increase symptoms for those at risk.

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, such as gas-powered lawn mowers, leaf blowers, etc.
• Avoid using chemical sprays, cleaners or oil-based products such as paints or solvents if you can avoid them. They contain volatile organic compounds (VOCs), which contribute to smog.
• 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.
• 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.

At work:

• If possible, take public transit, or walk to work.
• If you use a car, don't travel alone; encourage and facilitate carpooling.
• 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.