Air Quality Science and Monitoring in Ontario

In Ontario, the two most important pollutants associated with poor air quality are ground-level ozone and fine particulate matter. Other pollutants (nitrogen oxides, sulphur dioxide, carbon monoxide) are routinely measured, but they are not generally present at high enough ambient concentrations to be considered dominant factors.

Air quality and meteorology are closely linked, so certain weather conditions can be generally associated with either poor or good air quality.  For example, during the summertime, the worst air quality occurs on hot, humid days with plenty of sunshine.  In addition, there is often a south or southwesterly component to the wind which transports air pollutants from the highly industrialized areas in the United States into Ontario.  At other times of the year, poor air quality is often attributable to local sources that emit air pollution. 

Summertime episodes of poor air quality are often associated with elevated concentrations of ground level ozone.  Ground level ozone is formed by a series of chemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOC) in the presence of bright sunlight.  These chemicals are primarily attributed to industrial sources and automobile use, but there are many other sources that can contribute to the emissions of these components.  There are also natural sources of both NOx and VOC which add to the mix, however they do not normally result in poor air quality on their own.

Beyond summer, poor air quality events are often related to fine particulate matter.  Fine particulate matter is a complex mixture of particles and liquid droplets which are small enough to be inhaled deep into the lungs.  The major sources of fine particulate matter are combustion processes such as those from industrial facilities, automobiles and forest fires.  There are other sources of fine particulate matter, but their relative contributions are much smaller.

Information about air quality and individual pollutants is collected by monitoring networks found throughout Canada, including the National Air Pollution Surveillance Network (NAPS) and the Integrated Atmospheric Deposition Network (IADN).

For more information on air quality in Ontario please visit http://www.airqualityontario.com