Air Quality
Outdoor (Ambient) Air
Definition
Outdoor air pollution consists of a mixture of gaseous and particulate pollutants. Pollutants of interest with regard to health include ground level ozone (O3), particulate matter (PM), especially PM2.5 (PM with a diameter of < 2.5 microns), nitrogen dioxide (NO2), sulphur dioxide (SO2), and carbon monoxide (CO). These pollutants may be emitted from, or formed as a result of, many activities, including industrial and manufacturing processes, the combustion of fossil fuels in motor vehicles, and the use of wood-burning stoves.
The relationship between air quality and health is complex because of the interplay of numerous factors. Exposure to ambient air pollution has been associated with adverse health outcomes that range from subtle biochemical and physiological changes to difficulty breathing, wheezing, coughing and aggravation of existing respiratory diseases. These effects can result in increased medication use, more visits to doctors or emergency rooms, more hospital admissions and even premature death (Figure 3-1). Certain subgroups of the population who are more sensitive to the effects of air pollution may experience health effects even at very low levels of exposure. Although air quality can affect cardiovascular health and may affect other systems, this chapter focuses on the links between air pollution and respiratory health, with an emphasis on Canadian studies.
Trends
Air pollutants are subject to complex atmospheric chemistry, and the pollutant mix varies both regionally and locally (e.g., within cities). Ambient air quality in Canadian cities and towns is monitored by the National Air Pollution Surveillance Network (NAPS), as well as by local and provincial agencies.
Reductions in emissions from vehicles, electric power generation and industry have reduced levels of several primary air pollutants since the 1980s. Levels of the gaseous pollutants (nitrogen oxides, sulfur oxides and CO) declined from the mid-1970s to the mid-1990s. A rise in sulfur oxide (SOx) levels was observed between 1995 and 1998 as emissions from thermal power generators increased; however, levels have declined to 1995 levels since then (Figure 3-2), likely as a result of regulatory measures targeting this pollutant.
Since a decline in PM and O3 levels from the mid-1970s to mid-1990s, there have been no discernible upward or downward trends for these key components of smog. There was no significant change in O3 levels between 1991 and 1995. An evaluation of trends in PM2.5 levels (Figure 3-3) is limited by the fact that daily monitors of PM2.5 were not present in all regions of Canada until the 1990s.3
Figure 3-3. Concentrations of average ambient ground-level O3 across large urban, small urban and non-urban stations in Canada, 1991-2005, and average PM2.5 across urban Canadian sites, 1984-2002.4,5
Health Outcomes
Health Canada estimates that short-term and long-term exposure to air pollution is responsible for approximately 5,900 premature deaths annually in the eight largest Canadian cities combined. Although this figure is driven by cardiovascular mortality, respiratory conditions are a contributing factor.6 Many studies have shown an association between acute exposure to air pollutants and mortality in Canadian cities.7, 8, 9, 10, 11, 12, 13, 14, 15, 16 A link between mortality and long-term exposure to PM is also well documented.17, 18, 19, 20, 21, 22, 23 In addition, long-term exposures to PM10, PM2.5, SO2 and O3 have been associated with lung cancer incidence and mortality.24, 25, 26
There is strong evidence that exposure to outdoor air pollution exacerbates asthma and, to a lesser extent, COPD. This suggests that some people are especially susceptible to the effects of air pollution. Asthma-related outcomes associated with air pollutants include hospitalization,27, 28 emergency room visits,29, 30 incident asthma attacks,31 asthmatic symptoms32 and medication use.33 In controlled human exposure studies, some asthmatics were more sensitive to allergen exposures if previously exposed to NO2 or O3.34, 35, 36, 37 The severity of an asthma attack after viral infection has been associated with higher levels of prior exposure to NO2.38 Children living in high O3 areas who spent more time outdoors and who played three or more sports were more at risk for developing asthma or experiencing increased adverse effects on lung function and respiratory symptoms than those who spent less time outdoors.39, 40 While significant, these latter findings may be of limited relevance to Canadians as they were found in parts of the U.S. with levels higher than are normal in Canada.
Exposure to air pollutants has been associated with both hospitalizations for, and exacerbation of, COPD.41, 42, 43 In addition, air pollution has been associated with the admission of elderly subjects to hospital.44, 45
Many studies have documented the sensitivity of children to the adverse effects of air pollution. Increased cough and respiratory symptoms,46, 47 and physician and hospital visits, 48, 49, 50, 51 have been associated with children’s exposure to outdoor air pollution, including traffic-related air pollution. Long-term exposure to acidic particles may have harmful effects on lung growth, development and function.52 Results from the Children’s Health Study in California indicated that chronic exposure to PM was associated with respiratory symptoms and lung function changes; changes in air pollutant levels during adolescence influenced lung function growth and performance, and increasing O3 levels were associated with school absenteeism.53, 54, 55, 56, 57
Pre- and post-natal development has also been associated with maternal exposure to air pollutants.58, 59, 60, 61, 62, 63, 64
The Role of the Government of Canada
Pollution control programs have considerably reduced the levels of many ambient air pollutants. In Canada, some reductions have been accomplished through new regulations, such as for vehicles and fuel. Canada-Wide Standards and the Ozone Annex to the Canada/United States Clean Air Agreement underlie further improvements.
Ambient Air Guidelines
Air quality objectives are based on recognized scientific principles through the completion of extensive peer-reviewed Science Assessment Documents leading to the development of either Canada-Wide Standards (CWS) or National Ambient Air Quality Objectives (NAAQOs).
NAAQOs have been the benchmark against which Canada assesses the impact of human activities on air quality and ensures that emission control policies protect human health and the environment. Traditionally, the federal government establishes these objectives following recommendations by a national advisory committee and working group. They may be adopted by provincial governments as objectives or as enforceable standards. The federal government is expected to take more direct control over the setting of these objectives under its Clean Air Regulatory Agenda, retaining their normal purpose but adding a dimension of delineating attainment and non-attainment areas for the purpose of setting rules on the trading of major emissions of NO2 and SO2.
The Canada-Wide Accord on Environmental Harmonization and its sub-agreement on Canada-Wide Standards was signed in January 1998 by all Canadian environment ministers except for Quebec. Canada-Wide Standards involve the development of jurisdictional risk management plans to attain the agreed-upon standard to reduce health and environmental risks within a specific timeframe. Provincial and federal stakeholder consultation is a fundamental aspect of the CWS process. Like NAAQOs, Canada-Wide Standards are science-based, but they also explicitly recognize and incorporate a number of other factors, including technical feasibility and economic issues.
Air Quality Index (AQI)
The AQI is a communications tool, which describes the general level of air pollution at a particular place and time using a numerical scale and a qualitative rating, but it does not report the concentrations of individual pollutants.
To address the shortcomings and variations between current AQIs, an agreement was reached in 2002 between governments and other stakeholders to develop a Canadian AQI that would be more health-risk based. This is the first air quality health index of its kind in the world based directly on risk coefficients from epidemiological studies.65 A cornerstone of this process is the development of relevant and timely messages to help Canadians to safeguard their own health and to motivate change in improving air quality in communities.66
Indoor Air
Definition
Results from the Canadian Human Activities Pattern Survey (CHAPS) indicate that adults in Canada spend about 90% of their time indoors.67 The levels of air pollutants indoors depend on outdoor air pollution, the rate at which indoor air is exchanged with outdoor air (windows opened or closed, presence of an air conditioning system), the presence of sources indoors (combustion appliances, consumer products), and building design and materials.
Indoor air pollutants include biological agents (e.g., mould); combustion products (such as PM2.5, CO and NO2) from appliances that burn fossil fuels; volatile organic compounds (VOCs) and formaldehyde emitted from consumer products; and radon, a naturally occurring radioactive gas. It should be noted that tobacco smoke is a major source of several chemical pollutants, including PM2.5, CO, and VOCs.
When sources are from the indoor environment, the concentration levels of many pollutants can be higher than outdoors. Thus, while concentrations of NO2 are usually lower indoors than outdoors when there is no indoor source, indoor concentrations can exceed outdoor levels in homes equipped with gas cooking stoves. 68
Health Outcomes
Associations have been observed between indoor air pollutants and health effects, primarily in relation to asthma. The U.S. National Academy of Science concluded that the development of asthma can be causally linked to exposure to house dust mites and associated with second-hand smoke (SHS) in preschool-aged children.69 Similarly, exacerbation of asthma has been causally linked with exposure to cats, cockroaches, house dust mites and SHS in preschool-aged children, and associated with exposure to dogs, fungi or moulds, rhinovirus and high levels of NO2 and nitrogen oxides (NOx). A number of other possible associations have been raised but only with limited or suggestive evidence.
Mould: Health Canada recently reviewed the evidence regarding the health effects of mould.70 Several of the studies reviewed found significant associations between exposure to mould or dampness, and irritative and non-specific respiratory symptoms, as well as the exacerbation and development of respiratory diseases such as asthma. In immunocompromised individuals in hospital settings, airborne exposure to certain fungi was found to be associated with an increased risk of fungal infection. Current knowledge supports the need to prevent damp conditions and mould growth and to remediate any fungal contamination in buildings.
Wood smoke: Exposure to wood smoke may also lead to some health effects, such as impairment of lung defences in children, asthma symptoms and increases in respiratory symptoms, as well as headaches, nausea and dizziness.71, 72, 73
Appliances, tobacco smoke, traffic: Elevated indoor levels of CO from sources such as combustion appliances, tobacco smoke, and vehicles in attached garages and nearby roads, can disrupt oxygen transport by haemoglobin, making sensitive individuals such as people diagnosed with coronary disease especially susceptible to adverse health effects.74 High levels of NO2 from traffic and indoor combustion sources such as unvented gas stoves increase bronchial responsiveness in both asthmatics and healthy individuals and increase response to inhaled allergens in asthmatics.75
Formaldehyde and VOCs: Formaldehyde is a gas emitted from off-gassing of wood-based materials such as plywood and particle board and some paints and varnishes. It is also emitted by combustion sources such as wood stoves. Exposure to formaldehyde causes irritation to the airways and the eyes.76 Many consumer products, including cleaners, aerosols and fragrances, as well as construction materials emit VOCs that may persist in the air, triggering effects including skin, eye, and respiratory tract irritations, headaches, nausea and dizziness.77
Radon: Radon is a radioactive gas that arises from the natural breakdown of uranium in soils and rocks. In confined spaces like basements and underground mines, radon can accumulate to high concentrations. Radon is a well-known human carcinogen, and indoor exposure to this gas is considered to be the second leading cause of lung cancer after smoking.78, 79
Burden of Disease and Health Care Costs
Estimating the burden of disease associated with indoor air pollution is difficult because of the lack of exposure data that are representative of the Canadian population and because of our limited knowledge of quantitative exposure–response relationships. As a result, we cannot quantify health care costs associated with indoor air pollution in Canada.
Guidelines And Resources
Canada’s Exposure Guidelines for Residential Indoor Air Quality were developed in the late 1980s by the former Federal-Provincial Advisory Committee on Environmental and Occupational Health (CEOH).80 Its report summarizes the key health effects of 19 substances and recommends limit values or controls. Health Canada is reassessing the scientific basis of the guidelines. A revised guideline for formaldehyde was published on Health Canada’s website81 in 2006, and a new guideline on moulds was issued in 2007.82 Health Canada’s residential indoor air quality guidelines are on-line, along with fact sheets and several scientific reports.83
A guide published by Canada Mortgage and Housing Corporation (CMHC) in 1993 gives Canadians practical advice on improving and maintaining residential air quality.84 More recently, CMHC and Health Canada jointly published a guidebook on radon for Canadian homeowners.85 Health Canada has also developed a guidebook outlining ways of recognizing and managing fungal contamination in public buildings (with the exception of hospitals and industrial plants).86
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66 Further information is available at www.aqhi.gc.ca.
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76 WHO International Programme on Chemical Safety. Formaldehyde: Environmental Health Criteria 89. Geneva: World Health Organization, 1989.
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http://www.hc-sc.gc.ca/ewh-semt/pubs/air/exposure-exposition/index_e.html.
81 Health Canada. Residential Indoor Air Quality Guideline: Formaldehyde. Ottawa: Health Canada; 2006.
82 Health Canada. Residential Indoor Air Quality Guidelines: Moulds. Ottawa: Health Canada; 2007.
83 Available at Health Canada ’s Health and Air Quality website: www.hc-sc.gc.ca/air.
84 Canada Mortgage and Housing Corporation. The clean air guide: how to identify and correct indoor air problems in your home. Ottawa: CMHC; 2002.
85 Health Canada and Canadian Mortgage and Housing Corporation. Radon. A Guide for Canadian Homeowners [monograph on the Internet]. Ottawa: Health Canada and Canada Mortgage and Housing Corporation; 2007. Available from:
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86 Health Canada. Fungal contamination in public buildings: health effects and investigation methods [monograph on the Internet]. Ottawa: Health Canada; 2004 [updated 2005 Aug 3]. Available from: http://www.hc-sc.gc.ca/ewh-semt/alt_formats/hecs-sesc/pdf/pubs/air/fungal-fongique/fungal-fongique_e.pdf.