Air Quality Trends
AAQD Reports List
Air Quality Trends in Canadian Cities 1979-1992
In 1969, the federal government introduced the Clean Air Act to address
the problem of air pollution. And in fact, 1999 marked the 30th anniversary
of a federal-provincial program that measures air pollution in Canada,
the National Air Pollution Surveillance (NAPS) Network.
The network provides important information on common pollutants to which
Canadians may be exposed in the air they breathe.
National Ambient Air Quality Objectives (NAAQOs) were established by
the federal government in the early 1970s. These objectives were
established to protect human health and the environment by setting
limits for the following common air pollutants: carbon monoxide,
nitrogen dioxide, ozone, sulphur dioxide and total suspended
particulates. All of these substances are measured under the National
Air Pollution Surveillance program and are described in detail under
the heading Trends in common air contaminants.
Objectives are described for three ranges of pollutant concentration
in the ambient air: desirable, acceptable and tolerable, and these
correspond to degrees of environmental damage or potential health
effects. Air pollution is then evaluated and stated as either good,
fair, poor or very poor, by comparison with the objectives for each
The Index of the Quality of Air (IQUA) collects and converts individual
pollutant concentrations to a number on the IQUA scale. The
scale at left ranging from 0 to 125 illustrates how the various numbers
correspond to air quality measurements (good, fair, poor or very poor).
The IQUA helps communicate hourly measurements of common pollutants
to the public in urban areas.
Air Quality in Canadian Cities
The graphs at left provide a summary of air quality trends in 17 major
cities across Canada from 1979 to 1992. Both the average and peak levels
for air pollutants are shown for each year, to indicate the range of air
quality in the downtown areas of selected Canadian cities.
Trends in Common Air Contaminants
Suspended particulate includes dust, smoke and pollen and other
substances emitted by natural sources and human activities.
Transportation, mining operations, thermal power generation plants
and waste incinerators are major sources of suspended particulate.
Despite a 54 per cent decline in particulate levels in the 1974-1992
period, total suspended particulate (TSP) remain a dominant factor in
determining local air quality.
Ground level ozone monitored by NAPS should not be confused with
stratospheric ozone. Ground level ozone is the major component of
photochemical smog, and is not emitted into the atmosphere.
Rather, it is created from chemical reactions in the air between
volatile organic compounds (VOCs) and nitrogen oxides (NOx).
High ozone concentrations tend to occur under conditions of bright
sunlight, high temperature and a stationary air mass.
The highest smog concentrations are normally found in the
Windsor-Quebec City corridor, the Saint John area of the Southern
Atlantic region and the Lower Fraser Valley in British Columbia.
Ground level ozone concentrations are strongly influenced by
meteorology and thus are highly variable from year to year.
Sulphur dioxide is a colourless gas with a strong odour.
Oil and gas processing, ore smelting and the burning of coal and
heavy oil are the major generators of sulphur dioxide.
From 1974 to 1992, the annual mean sulphur dioxide concentration
decreased 61 per cent. As a result, sulphur dioxide levels rarely
exceed maximum acceptable levels.
Carbon monoxide is a toxic, colourless and odourless gas generated
from burning material containing carbon. Most carbon monoxide is
created by motor vehicles, heating of dwellings and industrial
pollution. The annual average concentration of carbon monoxide
decreased by 70 per cent from 1974 to 1992. As a result, carbon
monoxide levels very rarely exceed maximum acceptable levels.
Nitrogen dioxide is generated through high-temperature combustion
processes including transportation and industrial fuel combustion.
There was a steady decrease in annual average nitrogen dioxide levels
nationwide from 1977 to 1992, a reduction of 38 per cent. As a result,
maximum acceptable levels are rarely exceeded.
Air pollution has long been recognized for its potential to harm both
the environment and human health. It comes from many sources, including
motor vehicles, industrial activities and the burning of fossil fuels
and wood that heat our homes and schools. Urban air quality in Canada
continues to show improvement, with average pollutant concentrations
in the atmosphere showing decreases. The federal government is continuing
to work with provinces, territories and municipalities to meet Canada's
air quality goals and to combat serious air quality issues such as smog,
acid rain and climate change.
When we combine the information on each pollutant nationally, an overall
improvement in air quality in major cities across Canada over the past
decade is observable. Decreases in annual means from 1974-1992 were as
The federal government will continue to measure air quality trends
throughout the country, and an updated version of this fact sheet that
incorporates new data will be produced by Environment Canada.
Air Quality Trends in Canadian Cities 1979-1992
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