Environment Canada
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The Science of Air Quality
The quality of the air is the result of complex interactions of many factors that involve the chemistry and meteorology of the atmosphere, as well as the emissions of a variety of pollutants from sources that are both natural and anthropogenic. The pollutants associated with air quality that are measured by the new AQHI are ground-level Ozone (O3 or GLO), fine and course Particulate Matter (PM2.5/PM10)and Nitrogen Oxides (NOx).
The AQHI is calculated based on the relative risks of a combination of common air pollutants which are known to harm human health.
Ground-level ozone is not emitted into the air directly. It is a “secondary” pollutant formed from a set of photochemical reactions, or reactions that occur under the presence of sunlight. High levels of ground-level ozone (GLO) typically occur from May-September in Canada and from morning to early evening. Ozone precursors are nitrogen oxides and volatile organic compounds which react with sunlight to form GLO. GLO irritates the respiratory tract and eyes. Exposure to high levels of GLO results in chest tightness, coughing and wheezing. People with respiratory and heart problems and children are at a higher risk. Ozone has been linked to increased hospital admissions and premature death. (Source: Clean Air Online, ground-level O3).
Particulate matter can either be directly emitted into the air “primary” or formed in the atmosphere via chemical reactions “secondary.” Examples of particulate matter include (soot from forest fires, particles from smokestacks and electrical power plants, sea salt, and dust, just to name just a few. Exposure to particulate matter has been associated with hospital admissions and several serious health effects, including premature death. (Source: Clean Air Online, Particulate Matter).
Nitrogen oxides include nitrogen oxide (NO) and nitrogen dioxide (NO2). The primary sources of nitrogen oxides are motor vehicles, power plants, and waste disposal systems. High concentrations are believed to contribute to heart and lung problems. Nitrogen oxides are highly reactive gases that play a key role in producing ground-level ozone. (Source: Clean Air Online, Nitrogen oxides).
