What is air quality?

Air quality is a measure of how good or bad the air is based on how much pollution is in it, or how it looks and smells. Albertans are concerned about the quality of our air and what contaminants are being released from various pollution sources. As technology improves, we are able to better track both the quantity of emissions released into the atmosphere and the quality of the air. The more we learn about our environment and our impact on it, the better able we are to make informed choices about how to improve air quality both from a society and individual basis.

The quality of the air we breathe is dependent on the rate that pollutants are emitted into the atmosphere and the ability of the atmosphere to disperse these pollutants. The movement and dispersion of air pollutants is controlled by wind, temperature, turbulence and the changes in these elements caused by local topography (mountains and valleys).

Wind

Wind determines the path air pollutants take from their source to any receptor. At high wind speeds pollutants disperse more rapidly, but can be transported farther. At low wind speeds pollutants disperse at a slower rate and can build up, especially where many sources are concentrated together such as in a city.

Temperature

The rate that air temperature changes with height has a substantial effect on mixing of air pollutants. Under normal conditions, the temperature in the lower atmosphere decreases with height. A temperature inversion occurs when temperature increases with height (the inverse of a normal temperature profile). During an inversion, atmospheric mixing is diminished and therefore pollutant dispersion decreases. The combination of a strong temperature inversion and light winds may lead to a cold layer of stagnant air near the ground that traps pollution and causes it to build up. Temperature inversions are common in wintertime in Alberta and can last all day or even span several days.

Turbulence

Turbulence is the random motion of air in the atmosphere. Turbulence from the frictional force of air at ground level, or from conventional heating, creates atmospheric mixing and allows air pollutants to disperse.

Topography

Large terrain features such as mountains, hills and valleys significantly affect wind speed and direction. A common cause of air pollution in valleys with numerous pollutant sources is persistent temperature inversions.