How Air Quality is Degraded
Air quality is degraded when unwanted chemicals or other materials are released into the air in large enough amounts to harm the health of people, plants and animals, and our environment. This is called “air
pollution,” and the harmful substances are called “air pollutants.” The quality of the air depends on the amount of pollutants, the rate at which they are released from various sources,
and how quickly the pollutants disperse (or, conversely, how long they are trapped in an area).
Many air pollutants occur as gases or vapours, but some are very tiny solid particles, such as dust, smoke or soot. Some are emitted from natural sources, such as volcanoes, while many others come from
Air pollution can affect indoor air quality, as well. Indoor air pollutants include cigarette smoke, mould, dust mites, pet dander, formaldehyde, volatile organic compounds (VOCs) and radon gas. (See Indoor
If air pollutants are in an area with good airflow, they will mix with the air and quickly disperse. However, when pollutants are trapped in an area, pollutant concentrations can increase rapidly. This
can happen when weather conditions (e.g., light winds and a temperature inversion aloft), and/or terrain features (e.g., mountains) limit the transport of pollutants away from an area. The outcome is air
pollution — or “poor” air quality, as defined by Canadian environmental standards. For more information on how air becomes polluted, see Factors
Affecting Air Quality and What are Pollutants and Emissions?.
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