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Environment

Air Quality Index FAQs

Last Updated July 9, 2007

It's summertime, and along with weather and temperature, there's another stat to keep watch for: air quality. A hot humid day may deter you from venturing outdoors, but should you also be concerned about a high Air Quality Index?

Yes. The air we breathe is not pure. It may contain thousands of chemical and biological substances. Some of them are in the air naturally, while others are the byproducts of factories and cars.

And it can kill. About 4,200 Canadian deaths were associated with long-term exposure to poor-quality air between 1998 and 2000, according to Health Canada. And another 1,800 deaths were associated with short-term exposure to poor-quality air.

But what exactly is in the air that causes harm? And what do these readings actually mean?

What is the Air Quality Index?

The Air Quality Index (AQI) is a scale that measures amounts of pollutants in outside air. The lower the rating, the better the air quality.

The readings are produced using data from different air-monitoring stations across each province. Every hour, AQI stations analyze the air looking for six common pollutants, and the amount found is rated on a scale. The pollutant with the highest level becomes the AQI reading.

What are the different ratings and what do they mean?

AQI Colour Meaning
0 - 15
Very Good
Blue The air quality is considered good
16 - 31
Good
Green The air quality is considered relatively good
32 - 49
Moderate
Yellow Very sensitive people will be affected
50 - 99
Poor
Red Short-term adverse affects on humans and animals, and could significantly damage plants, crops and property
100 +
Very Poor
Red Adverse effects on a large number of those exposed

If poor ratings are expected for a period of time and over a large area, a smog alert is issued.

The two types are:

  • Smog Watch: There's at least a 50 per cent chance smog could occur within the next three days
  • Smog Advisory: High probability of high smog levels within the next 24 hours

What pollutants are in the air? Where do they come from? What could they do to me, or the environment?

The most common pollutants are:

Name of pollutant Properties Source Effects
Sulphur dioxide Colourless and smells like burnt matches -Most of it comes from smelters and power plants
-Also comes from steel mills, petroleum refineries, and pulp and paper mills
-High levels could lead to breathing problems and respiratory illness
-Aggravates existing respiratory and cardiovascular diseases
-Can lead to acid rain
Ozone A colourless and odourless gas -Formed in the lower atmosphere just above the Earth's surface when energy from the sun reacts with industrial pollutants and motor-vehicle exhaust particles in the air -Irritates the respiratory tract and eyes
-High levels can lead to chest tightness, coughing and wheezing
-Linked to more hospital visits and premature death
Causes farm crop loss and damages plants and trees
Nitrogen dioxide A reddish-brown gas with a pungent odour -About 63 per cent of it comes from vehicles on the road
-Most of the remainder comes from power generation, metal production and incineration
-A small portion comes from natural sources
-Irritates the lungs and weakens the body's resistance to respiratory infections
- When it chemically changes to nitric acid, it can degrade metal and rubber, fade fabrics, and damage trees and crops
Total reduced sulphur compounds Smells like rotten eggs or cabbage -Comes from steel companies, pulp and paper mills, refineries and sewage
- treatment facilities
-Also comes from natural sources like swamps, bogs and marshes.
-It doesn't really harm your health – it just smells bad
-Extremely high levels can make people nauseated and cause headaches
Carbon monoxide A colourless, odourless and tasteless but poisonous gas -Produced when fossil fuels are burned
-About 65 per cent of it comes from vehicles on the road
-Most of the remainder comes from metal producers and fuel combustion in space-heating and industrial processes
-In the bloodstream it reduces the amount of oxygen going to the lungs and the body's tissues
-High levels can impair vision, work capacity, learning ability and performance of difficult tasks
-Those with heart disease are particularly sensitive
Fine particulate matter A mixture of solid particles and liquid droplets in the air -Most of it comes from fuel combustion from motor vehicles, power generation, and residential fireplaces
-It includes aerosols, smoke, fumes, dust, ash and pollen
-Linked with more hospital visits and several serious health effects, including premature death
-Adverse effects can stem from both short-term exposure (a day) and longer periods (a year or more)

Where can I get local Air Quality Index readings?

Up-to-date AQI readings for all provinces are listed here.

What is the Air Quality Health Index?

In July 2007, the City of Toronto launched the Air Quality Health Index (AQHI) as a means for residents to gauge daily health risks from local air pollution. Earlier pilots have been conducted in B.C. and Nova Scotia.

The AQHI measures health risks on a scale from 1 to 10+ on a daily basis. Higher numbers indicate people should scale back their own home energy and vehicle use, and take extra precautions to protect their health.

The AQHI creates different readings, based on the combined effects of multiple pollutants, for the general population as well as at-risk groups, including the elderly, children and people with pre-existing heart and breathing problems.

Torontonians can check the AQHI at Environment Canada's Weather Office.

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