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The air quality indicators track measures of long term exposure of Canadians during the warm season (April 1 to September 30) to ground-level ozone and to fine particulate matter (PM2.5), two key components of smog that have been linked to health impacts ranging from minor respiratory problems to hospitalizations and even premature death. Studies indicate that adverse health effects can occur even with low concentrations of these pollutants in the air.
- Nationally, the ozone exposure indicator increased an average of 0.8% per year from 1990 to 2005. For the full time period, this resulted in an overall increase of 12% (plus or minus 10 percentage points, resulting in an increase ranging from 2% to 22% at a 90% confidence level). 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 in two regions - in southern Ontario by 17% (plus or minus 13 percentage points, ranging from 4% to 30% at a 90% confidence level) and in southern Quebec by 15% (plus or minus 12 percentage points, ranging from 3% to 27% at a 90% confidence level). In other regions, the ozone exposure indicator showed no statistically significant increasing or decreasing trends.
- The PM2.5 exposure indicator showed no significant increasing or decreasing trends, either nationally or regionally between 2000 and 2005. The highest PM2.5 concentrations in 2005 were detected at stations in southern Ontario and southern Quebec.
Context
Status and trends
Influencing factors
What’s next?
Context
Smog is one of the most recognizable air quality problems. It refers to a noxious mixture of air pollutants that often gives the air a hazy appearance. The major components of smog in Canada are ground-level ozone (referred to in this report simply as "ozone" unless otherwise noted) and fine particulate matter (PM2.5). Ozone and the precursor pollutants that lead to its formation can be transported by winds over long distances and affect areas hundreds or even thousands of kilometres from the sources of the pollutants (Environment Canada 2007b).
The air quality indicators in this report focus on ozone and PM2.5 because studies indicate that adverse health effects can occur even with low concentrations of these pollutants in the air (e.g., WHO 2005).
Box 1. Stratospheric ozone versus ground-level ozone
While ozone in the stratosphere is the same gas as the one found at ground level, it causes very different effects. High in the atmosphere, it forms the "ozone layer" that protects life on earth by preventing some of the sun’s ultraviolet rays from reaching the earth’s surface, thereby reducing negative effects such as skin damage (CCME 2004a). Under certain meteorological conditions, stratospheric ozone (O3) can, at times, be transported downward to the earth’s surface and can contribute to ground-level ozone.
Nature of ozone
Ozone is found throughout the atmosphere (Box 1) but is not emitted directly to the air. Instead, it is formed through a series of complex chemical reactions involving two precursor pollutants, nitrogen oxides (NOx)1 and volatile organic compounds (VOC).
In many parts of Canada, the short-term peak (1- to 8-hr average) ozone levels produced from chemical reactions involving NOx and VOC are typically highest in the summer because ozone formation is favoured by strong sunlight and high air temperatures. Ozone concentrations vary considerably on an hourly, daily and monthly basis, depending on precursor emission levels and prevailing meteorological conditions such as temperature and wind direction (Environment Canada 2007b).
Nature of fine particulate matter
Particulate matter (PM) refers to very tiny liquid and solid particles of various sizes that are suspended in the air. PM is emitted as a primary pollutant or is formed in the air as a secondary pollutant from precursor gases such as sulphur dioxide, NOx, VOC, ammonia (NH3) and numerous carbon-containing substances (Environment Canada 2007b). Of particular interest is fine particulate matter (PM2.5), particles with a diameter of no more than 2.5 micrometres.2 From a health perspective, PM2.5 particles are of greatest concern because they are sufficiently small to reach the finer structures of the human lung (Liu 2004).
Elevated ambient levels of PM2.5 can occur year-round and are affected by location, time of year and prevailing meteorological conditions. Levels in urban areas are typically highest in the mornings and evenings, largely reflecting local emission sources such as transportation (Environment Canada 2007b).
Sources of ozone and fine particulate matter
Human activities are the major sources of PM2.5, and ozone and PM2.5 precursors such as NOx and VOC. Principal sources include
- the transportation sector (e.g., cars, trucks, marine vessels, trains, tractors, recreational vehicles and airplanes);
- industrial sectors (e.g., oil and gas exploration, drilling and extraction; base metal smelting; wood product mills, pulp and paper processing; and petroleum refining);
- thermal-electric power generation (i.e., electricity generation from power plants fuelled by coal, oil, natural gas or wood);
- agricultural activities; and
- consumer and commercial products (e.g., woodstoves, fireplaces, industrial and residential cleaners, cosmetics and paints).
Natural sources also emit precursor pollutants that contribute to the formation of ozone and PM2.5. For example, trees and vegetation emit very substantial quantities of VOC during the growing season, and these emissions contribute to both ozone and PM2.5 formation. Forest fires emit large quantities of primary PM2.5 as well as precursors of both ozone and secondary PM2.5. Volcanoes (none active in Canada) release massive quantities of particulate matter; and high winds can lift soil particles into the air, causing dust storms in extreme cases.
Health and environmental effects
Observed health effects of human exposure to ozone and particulate matter include respiratory symptoms such as coughing, triggering of asthma attacks and episodes of chronic bronchitis, emphysema, angina and other heart conditions. In general, as concentrations of these pollutants increase, so does the risk of health impacts. These effects may, in turn, result in a range of activity restrictions, increased emergency room visits, hospitalizations and premature death. Socio-economic consequences include lost productivity and higher health care costs (De Civita et al. 2002).
Children are especially sensitive to air pollution because they grow rapidly, their bodies are developing, they breathe in more air in proportion to their body size and they are more likely to be active outdoors (U.S. EPA 2006). The elderly and individuals with pre-existing health conditions are also at greater risk of being affected than healthy adults (WHO 2005).
In summary, the risk to an individual’s health from air pollution is a complex function of a number of factors, including the quality of the air (level of pollutants), the individual’s level of exposure (e.g., activity outdoors) and their particular situation (e.g., health, age).
In addition to causing health risks, ozone and PM2.5 are also associated with ecosystem impacts. Deposition of the acidic compounds contained within PM2.5 contributes to ecosystem acidification, harming terrestrial and aquatic ecosystems. Elevated concentrations of ozone reduce plant growth and yield, decreasing productivity in agriculture and forestry. Elevated concentrations of particulate matter reduce visibility by decreasing how far and how clearly we can see. Both ozone and PM2.5 are also known to cause damage to various types of materials through fading, cracking, erosion or corrosion.
The ozone and PM2.5 exposure indicators
The air quality indicators track measures of Canadians’ long-term exposure during the warm season (April 1 to September 30) to ozone and to fine particulate matter (PM2.5), two of the most pervasive and widely spread air pollutants to which Canadians are exposed (Box 2).
Box 2. The air quality indicators
Two air quality indicators are presented in this report: one for ozone and one for PM2.5.
The ozone exposure indicator is based on the highest 8-hr daily average concentrations recorded at monitoring stations across Canada. The ozone exposure indicator is presented for the period 1990 to 2005. Data were collected through the National Air Pollution Surveillance (NAPS) Network, a joint federal, provincial, territorial and municipal program, and through the Canadian Air and Precipitation Monitoring Network (CAPMoN) operated by Environment Canada.
The PM2.5 exposure indicator is based on the 24-hr daily average concentrations recorded at monitoring stations across Canada. As the PM2.5 network has expanded sufficiently since 2000, the national PM2.5 exposure indicator is presented for the period 2000 to 2005. Data were collected through the National Air Pollution Surveillance (NAPS) Network.
Both indicators are based on yearly warm-season averages (April 1 to September 30). Ozone concentrations are normally highest during these months and Canadians are typically most active outdoors (Leech et al. 2002). While winter PM2.5 is a concern, current monitoring methods may underestimate levels due to instrument variability in cold weather.
When calculating national and regional annual averages during the warm season for both ozone and PM2.5, average concentrations for each station are population-weighted to estimate potential human exposure to the pollutants. Each monitoring station included in the analysis is assigned a weight, based on the population estimated to be within a 40-km radius. The population data are from Statistics Canada’s Census of Population. As a result, more weight is given in the annual average to the air pollution measurements observed in the more highly populated areas so that the indicators are more representative of the exposure of the population to the air pollutants.
These annual population-weighted values vary from year to year, primarily as a result of changing conditions such as weather patterns. To detect whether there was a trend in the exposure indicators, a statistical test was applied to the national and regional exposure indicators. For this report, only statistically significant trends are reported as a percentage change per year, obtained by dividing the slope of the trend line by the median of all the annual exposure indicator values. The percentage change over the entire time period was also calculated by summing over years and the 90% confidence interval reported to more fully describe the trend.
See Appendix 1, Map A.1 for the locations of the monitoring stations and regions used in trend analyses and for additional details on the methods. It is important to note that the definition of regions has changed since the last report to improve geographical representivity. Stations in eastern Ontario are now grouped with stations in southern Ontario, rather than with the Quebec ones, as in previous reports.
Status and trends
Ozone exposure indicator
Fine particulate matter exposure indicator
Ozone exposure indicator
National status and trends
Regional status and trends
Nationally, the ozone exposure indicator increased an average of 0.8% per year from 1990 to 2005 (Figure 1). Over the full time period, this represented an overall increase of 12% (plus or minus 10 percentage points, resulting in a possible increase ranging from 2% to 22% at a 90% confidence level).
This increasing trend would suggest that the Canadian population represented in this analysis experienced an increasing health risk from exposure to ozone over this period.
Because of the greater population and number of monitoring stations in southern Ontario and southern Quebec, the national ozone exposure indicator is primarily driven by the ozone concentrations and populations in these two regions. In 2005, stations in southern Ontario had the highest ground-level ozone concentrations; southern Quebec and Alberta also had many stations reporting high concentrations (Map 1).
Figure 1 Ground-level ozone exposure indicator, Canada, 1990 to 2005
Map 1 Ground-level ozone concentrations at monitoring stations, Canada, 2005
From 1990 to 2005, the ozone exposure indicator showed an increasing trend in southern Ontario and southern Quebec; no statistically significant increasing or decreasing trends were detected in other regions (Figure 2). During this period, the ozone exposure indicator in southern Ontario increased an average of 1.1% per year resulting in an overall increase of 17% (plus or minus 13 percentage points, ranging from 4% to 30% at a 90% confidence level). Southern Ontario is home to approximately 30% of Canadians (Statistics Canada 2002). In southern Quebec, where most Quebecers live, the ozone exposure indicator increased an average of 1.0 % per year resulting in an overall increase of 15% (plus or minus 12 percentage points, ranging from 3% to 27% at a 90% confidence level).
These increasing trends suggest that the population health risk associated with ozone exposure increased in these regions between 1990 and 2005.
Figure 2 Ground-level ozone exposure indicator by region, 1990 to 2005
Fine particulate matter exposure indicator
National status and trends
Regional status and trends
Between 2000 and 2005, the national PM2.5 exposure indicator showed no significant increasing or decreasing trends (Figure 3). This suggests that the Canadian population represented in this analysis did not experience any change in health risk from exposure to fine particulate matter over this period.
Figure 3 Fine particulate matter (PM2.5) exposure indicator, Canada, 2000 to 2005
Because of the greater population and number of monitoring stations in southern Ontario and southern Quebec, the national PM2.5 exposure indicator is primarily driven by the PM2.5 concentrations and populations in these two regions. The highest PM2.5 concentrations in 2005 were detected at stations in southern Ontario and southern Quebec (Map 2).
Map 2 Fine particulate matter (PM2.5) concentrations at monitoring stations, Canada, 2005
No statistically significant increasing or decreasing trends from 2000 to 2005 were detected for the PM2.5 exposure indicator for any region (Figure 4). This suggests that the population health risk associated with exposure to PM2.5 did not change over this period in any region.
Figure 4 Fine particulate matter (PM2.5) exposure indicator by region, 2000 to 2005
Influencing factors
Local emissions
Weather-conditions
Long-range transport of pollutants
Local ambient levels of a pollutant in a given community are influenced by local emissions, weather conditions and the long-range transport of pollutants from other communities, provinces, countries and even, in some cases, other continents. All of these factors may explain the increasing trends of ozone exposure in southern Ontario and southern Quebec.
Local emissions
Location is a factor influencing individual exposure to certain air pollutants, with those who are in close proximity to pollutant sources most often experiencing higher ambient levels than those farther away. For example, air pollutant levels (e.g., NOx) are generally higher close to a busy road than they are in low-traffic areas.
In general, reducing emissions of air pollutants will result in a comparable decrease in ambient levels of the pollutants. For example, from 1991 to 2000, emissions of the ozone precursors NOx and VOC from on-road vehicles decreased by 23% and 35%, respectively. Similarly, NOx and VOC concentrations in the air decreased by 13% and 33% in urban areas (greater than 100 000 population) over the same period (Environment Canada 2007b).
However, emissions and ambient pollutant concentrations vary among locations, and these geographical variations influence the chemical processes in the air that form and remove secondary pollutants (i.e. ozone and PM). For example, ozone is a secondary pollutant that is formed in the air through a series of chemical reactions involving NOx (NO and NO2) and VOC. However, when there are high local NOx emissions (e.g., from motor vehicles), the excess amount of NO removes ozone from the air, keeping the local ozone concentrations lower than expected through a process known as "NO (i.e., nitric oxide) scavenging of ozone." A consequence of this process is that the lowering of local emissions of NO could cause an increase in local ozone concentrations because a comparatively smaller amount of ozone is then being removed from the air. Nevertheless, the lower local NO emissions can still result in lower ozone concentrations downwind because less ozone is then formed from these emissions.
In rural areas, ozone concentrations may actually be higher than in nearby urban areas due to the absence of NOx emissions and, therefore, lack of NO (nitric oxide) scavenging of ozone. These ozone concentrations in rural areas can be further increased by the long-range transport of pollutants.
Weather conditions
Variability in ambient air pollutant levels is detected daily, seasonally and annually. This variability can be attributed to meteorological conditions: factors such as wind speed and direction, air temperature, atmospheric stability,3 temperature inversions,4 relative humidity, cloud cover and precipitation amounts can affect both the dispersion of emitted pollutants and the chemical reactions that the pollutants undergo. Both local conditions and the conditions through which the pollutants pass before arriving in a community influence these levels.
For example, stagnant air (i.e., high atmospheric stability, calm winds) leads to higher ambient pollutant levels than windier conditions because locally emitted pollutants accumulate rather than being carried away. Conversely, some meteorological conditions improve air quality: a very unstable atmosphere allows for efficient dispersion of pollutants; rain increases the deposition and removal of PM2.5 from the air; and days with rain, clouds and cool temperatures do not favour ozone formation. In addition, meteorology can affect the quantity of emissions; for instance, warmer summers lead to increased use of air conditioning and, as a result, higher emissions from thermal-electric power generation.
Long-range transport of pollutants
Air pollutants do not necessarily remain in the area where they are emitted. The wind (i.e., airflows) can transport them tens, or even thousands of kilometres away from their sources, a process known as long-range or transboundary transport. As such, air quality (ambient pollutant levels) in a particular area can be affected by pollutants emitted in another community, province or country or even, in some cases, another continent. For example, large quantities of pollutant emissions from the eastern United States are often transported to parts of southern Ontario, southern Quebec and the Atlantic provinces, raising ambient pollutant levels in those regions. In Windsor, ozone concentrations are about 40% higher under southerly airflows than they are under northerly ones (Johnson et al 2007). Another factor is that higher temperatures generally accompanying southerly airflows are more conducive to ozone formation.
What’s next?
The following specific improvements are planned in relation to air quality exposure indicator development, monitoring, analysis and surveys.
Indicator development
Research is ongoing to determine the cumulative effect of air pollution and to integrate associated risk factors into a comprehensive air quality and health indicator. The intent is that an air quality and human health indicator will provide a means of tracking changes in health risks related to air pollution and, consequently, the effectiveness of air pollution reduction measures. As part of the development of such an indicator, Health Canada is examining the association between mortality and the combined effects of multiple pollutants related to mortality. Factors influencing the risk of mortality, such as the chemical composition of pollutants, weather and social conditions are also being explored.
Monitoring
Currently, there are no monitoring stations in some parts of Canada. However, Environment Canada will continue to invest in new instruments to increase coverage at existing monitoring facilities and to establish new stations. Improved monitoring in remote locations will enhance understanding of background levels and inform interpretations of the trends. For the purposes of this indicator, the monitoring network should ideally provide balanced coverage of the Canadian population.
Surveys
The 2007 Households and the Environment Survey will include more detailed questions about home heating and air conditioning, the use of gasoline-powered recreational and small household engines, as well as more information on the types of motor vehicles owned by Canadians. As in 2006, respondents will be asked whether they are aware of air quality advisories and whether they have changed their normal behaviours in light of this awareness; this year, however, the survey will expand the question to ask which specific behaviours were changed.
Analysis
Calculations of the indicator do not currently make full use of the existing National Air Pollution Surveillance Network and population data because of geographical and temporal gaps in the monitoring data available. To allow for use of more existing data in the calculation of the exposure indicator, the application of broader trend analysis is being examined for inclusion in future CESI reports, as well as the differences in concentrations between stations with overlapping population area boundaries.
Research is also being conducted to help determine how the indicator responds to temporal and meteorological factors (e.g., day of the week, temperature), compared with changes in emissions, sources of pollutants and related precursors.
Notes
- In this document, "nitrogen oxides" (NOx) refers to nitric oxide (NO) and nitrogen dioxide (NO2).
- By comparison, the average diameter of a human hair is approximately 80 micrometres.
- Atmospheric stability describes the resistance of the atmosphere to vertical mixing. Reduced vertical mixing traps emitted pollutants closer to the surface.
- Air temperatures usually decrease with height from the earth’s surface; however, with temperature inversions, they increase. This inversion produces a stable atmosphere that allows the build-up of emitted pollutants near the ground.
