Air quality monitoring is carried out in Canada and the United States by air pollution control agencies in order to:
provide information on the quality of the ambient air and determine long-term trends;
identify pollutants and their sources, and determine the effects of emission controls on air quality levels;
control episodes brought on by unique weather conditions by obtaining data on a real time basis and ordering emergency shutdowns of sources of pollution. Air pollution episodes during which hazardous air quality levels are reached may thus be prevented;
determine background levels to assist in determining the transport diffusion and fate of the pollutants emitted, and the chemical reactions which take place in the atmosphere;
research the effects of pollutants on health, property, and vegetation to enable the agencies to set meaningful air quality criteria and standards.
Air Quality and Meteorology Section, Air Resources Branch.