Air quality can be impacted by many sources both through human activity and natural phenomenon.

• Point Sources: factories, industry, power plants, home and business heating and cooling
• Mobile Sources: transportation, vehicles, aircraft
• Natural Sources: trees, vegetation, wetlands, gas seeps, forest fires
• Area Sources: small sources, BBQs, firepits, drycleaners, pesticide use

In addition to wind speed and direction and important meteorological parameters that affect the transport and dispersion of air, monitoring at the stations is based on what is expected to be present in an area and available technology. For example, monitoring stations in urban centres typically measure for Nitrogen Oxides, Carbon Monoxide, Par- ticulate Matter, and Ozone, the parameters commonly associated with vehicle emissions and home heating and cooling. In an industrial area we may monitor for Sulphur Dioxide, Total Reduced Sulphurs, Hydrogen Sulphides, Total Hydrocarbons, Methane, Non-Methane or Fine Particulate Matter, depending on the industry. In rural areas we may monitor for Particulate Matter, Ozone, or Nitrogen Oxides.