Canada's measured air quality is relatively clean on a global scale, previously ranked 3rd worldwide for cleanest air in 2011. In the WHO's 2016 database, only 3 out of 125 monitored cities had annual mean levels of PM2.5 and PM10 above recommended safe levels: Courtenay, Regina and Vanderhoof, with Trois-Rivieries also creeping above the recommended limit for PM2.5 only. Canada has its own Air Quality Health Index (AQHI) system, which measures air quality through a combination of ozone (O3), PM2.5 and PM10, and nitrogen dioxide (NO2).
Regardless of ranking, any level of air pollution poses a degree of health and environmental hazard and Canada has multiple sources of air pollutants, many of which can be effectively addressed to minimise damage to health and environment. Main sources of air pollutants across Canada include transport, the oil and gas industry, and construction.
Other sources more specific to Canada include domestic wood-burning; recent policies have been put in place to discourage the use of inefficient wood stoves. Wildfires are another major source of pollutants; although a natural phenomenon and so largely beyond human control, the Canadian government has established dedicated wildfire smoke Air Quality Alerts and Smoke Predictions to help citizens protect themselves. Transboundary air has long been an issue, with air pollution from both the US and Canada drifting over each other’s national borders. The US – Canada Air Quality Agreement from 1991 seeks to address this, focusing on minimising transboundary ozone and acid rain.
Finally, the ongoing mining of Canada’s tar sands has also recently been found to produce more air pollution than originally thought. Producing twice the amount of air pollution as conventional oil extraction, including many aerosols, the air pollution over Alberta’s tar sands was found to be one of the leading sources of air pollution in North America, often higher than Canada’s biggest city. Recognition of these air pollution sources across Canada is essential to ensure that its air quality continues to improve.