Air quality

View the most recent version.

What is happening?

The air quality indicators track measures of the exposure of Canadians to ground-level ozone and fine particulate matter (PM_2.5) during the warm season (April 1 to September 30).

• Nationally, the ozone exposure indicator increased an average of 0.8% per year from 1990 to 2005. This resulted in an overall increase of approximately 12% for this time period.¹ In 2005, ozone concentrations were highest at stations in southern Ontario; southern Quebec and Alberta also had many stations with high concentrations.

• Between 1990 and 2005, the ozone exposure indicator increased only in two regions—in southern Ontario by approximately 17%² and in southern Quebec by approximately 15%³. In other regions, the ozone exposure indicator showed no statistically significant increasing or decreasing trends.

• The PM_2.5 exposure indicator showed no statistically significant increasing or decreasing trends, either nationally or regionally between 2000 and 2005. The highest PM_2.5 concentrations were measured at stations in southern Ontario and southern Quebec in 2005.

Figure 1 Ground-level ozone exposure indicator, Canada, 1990 to 2005

Figure 2 Fine particulate matter (PM_2.5) exposure indicator, Canada, 2000 to 2005

Why is it important?

Ground-level ozone and PM_2.5 have been linked to negative health impacts ranging from minor respiratory problems to cardiovascular disease, hospitalizations and premature death. For example, based on data from eight Canadian cities, Health Canada has estimated that 5,900 premature deaths each year in these cities are attributable to air pollution. Related economic effects include absenteeism, lower labour force participation and increased health care costs. Ecological and related economic impacts are also substantial. For example, elevated concentrations of ozone reduce plant growth and yield, decreasing productivity in agriculture and forestry. 

Why is it happening?

Ground-level ozone is formed by chemical reactions involving principally nitrogen oxides (NO_X) and volatile organic compounds (VOC) in the presence of sunlight. Human activities contribute to its formation by increasing the concentrations of NO_X and VOC, primarily through the burning of fossil fuels in sectors such as transportation, industry and electricity generation. Production and use of paints, cosmetics and the evaporation of liquid fuels and solvents also add VOC to the air.

In addition to the presence of local pollutant emissions, ozone concentrations are also affected by the long-range transport of pollutants from other regions and countries, and by weather conditions, such as temperature and wind direction. All these factors may explain the increasing trends of ozone exposure in southern Ontario and southern Quebec.

PM_2.5 is emitted directly as a pollutant or is formed in the air as a secondary pollutant from sulphur dioxide, NO_X, VOC and ammonia. The actual contribution of a specific pollutant to PM_2.5 concentrations in the air varies by location, time of year and prevailing meteorological conditions. On an annual basis, direct PM_2.5 emissions from industrial sectors are the largest, followed by wood burning for home heating, and transportation. Dust from wind erosion and smoke from forest fires are natural sources of PM_2.5 and contribute to total emissions.

Notes

1. Plus or minus 10 percentage points, resulting in an increase ranging from 2% to 22% at a 90% confidence level.
2. Plus or minus 13 percentage points, resulting in an increase ranging from 4% to 30% at a 90% confidence level.
3. Plus or minus 12 percentage points, resulting in an increase ranging from 3% to 27% at a 90% confidence level.