Home / Climate / Developing Ambient Air Quality Objectives For Canada / Ambient Air – Section 2

Ambient Air – Section 2

2 The history and current status of National Ambient Air Quality Objectives

Previous - Contents - Next Both PM and ozone have a long history of regulation in North America. They are two of the air contaminants originally regulated in Canada as "criteria pollutants," some 30 years ago. Although these two air pollutants have been historically regulated, and air quality improvements are evident, they continue to be important indicators of air quality. This importance reflects an evolving understanding of their impact on health outcomes, particularly as new scientific techniques and epidemiological methods identify more precise cause-and-effect relationships between exposure and wide-ranging health outcomes. Ongoing scientific research has confirmed that even at comparatively low concentrations, these air contaminants are associated with morbidity and mortality responses4 in the general population. In addition, the pollution concentration estimates associated with these effects are at levels that most Canadians frequently encounter. Thus there is a compelling public health commitment to manage and reduce exposures to these pollutants.

2.1 The issue of particulate matter and ozone

Health risks from air pollution are associated with direct exposure to ambient levels of PM and ozone, the main components of smog. Health science indicates that even at very low levels in the air these pollutants may have negative effects on human health, as well as a negative impact on the health of the ecosystem.

Particulate matter

PM consists of airborne particles in solid or liquid form, and may be classified as primary or secondary depending on the compounds and processes involved during its formation. Primary PM is emitted at the emissions source in particle form; for example, in the smokestack of an electrical power plant or a recently tilled field subject to wind erosion. The formation of secondary PM results from a series of chemical and physical reactions involving different precursor gases, such as sulphur and nitrogen oxides. Numerous studies have linked PM to aggravated cardiac and respiratory diseases, such as asthma, bronchitis, and emphysema and to various forms of heart disease. PM can also have adverse effects on vegetation and structures, and contributes to the deterioration of visibility and regional haze. Just as knowledge of PM and its health effects have increased over time, the development of PM air quality objectives has also evolved. During the 1970s and 1980s, regulatory efforts focused on controlling exposure to total suspended PM. In the late 1980s, this changed to establishing limits on inhalable PM or PM10 (for particles < 10 µm diameter), and, more recently, to limits on PM2.5, the respirable fraction of PM (for particles < 2.5 µm diameter). For example, in 2006 the US EPA5 organized a panel of experts to participate in expert deliberations as to the concentration-response relationship between average annual PM2.5 exposures and annual mortality. Although considerable uncertainty remains as to the details of the dose-response relationship, this EPA study established a reasonable consensus regarding the relationship between mortality and PM2.5. The review of regulatory decisions across Canada, the United States, and Europe indicates the absence of a current consensus as to the level at which a medium- to long-term goal for PM should be set. Appendix 1, which summarizes some of the existing domestic and international PM objectives, standards, guidelines and/or reference levels, illustrates the lack of consistent international objectives, as well as the diversity of ways being used to approach the management and control of this contaminant. The review of the documentation for setting PM2.5 regulatory standards in various jurisdictions shows that most committees appointed to investigate the relationship between health effects and PM recommend health-based standards for PM2.5 within a range of 15 to 25 micrograms per cubic metre (µg/m3)(24-hour averages). In support of their recommendations, these committees cite the precautionary principle, as well as the lack of a known threshold below which adverse health effects do not occur. These values are based on professional judgments by health professionals rather than on statistical calculations. The update of the World Health Organization (WHO) air quality guidelines in 2005 also recommended a PM2.5 value of 25 µg/m3 for short-term exposures. Moreover, the WHO emphasized that, for non-threshold pollutants such as PM2.5, exposure should be reduced even where current concentrations are close to or below the proposed guidelines; it also encouraged countries to consider increasingly stringent standards and to track progress via emission reductions and declining concentrations. In most jurisdictions, the numerical values chosen for particular standards or guidelines reflect political considerations; they try to balance the need to address public health concerns against PM levels that can be reasonably achieved within a 10-to-15-year period.

Ozone

Ozone is a colourless and highly irritating gas that forms just above the earth's surface. It is called a "secondary" pollutant because it is produced when two primary pollutants — nitrogen oxides (NOx) and volatile organic compounds (VOCs) — react in sunlight and stagnant air. Ozone is known to have significant effects on human health. Exposure to it has been linked to premature mortality and a range of morbidity health end-points, such as hospital admissions and asthma-symptom days. In addition to its effects on human health, ozone can significantly affect vegetation and decrease the productivity of some crops; it may also contribute to forest decline in some parts of Canada. Ozone and PM are the two primary pollutants in smog, which has been linked to many adverse effects on health and the environment. High levels of smog are typically associated with the summer, because of the presence of sunlight and warmer temperatures. However, the smog problem occurs throughout the year, with winter smog (due to PM contributions rather than ozone) being a serious concern when stagnant air causes a build-up of pollutants in the air. This is usually caused by increased wood heating and vehicle usage during the winter months. Judging from the review of available documents pertaining to issues surrounding the implementation of ozone targets, the European Union (EU) appears to be the most active jurisdiction dealing with ozone levels. The EU issued a directive on ozone in 2002, the main purpose of which was to establish long-term objectives, target values, an alert threshold, and an information threshold for concentrations of ozone in ambient air at the community level. These values were designed to avoid, prevent, or reduce harmful effects on human health and the environment as a whole, and to ensure that common methods and criteria are used to assess ozone concentrations and, as appropriate, ozone precursors (NOx and VOCs) in ambient air. Appendix 2 summarizes a few of the existing Canadian and international objectives, standards, guidelines, goals, and reference levels for ozone. The purpose of this table is to show the diversity of ways currently used to approach community air quality improvement. It also shows the lack of consistent international standards upon which Canada can draw. In most jurisdictions, the existing standards, objectives, and guidelines for PM and ozone employ standards already in force or those to be achieved in the relatively near term. It is important to note that no jurisdictions have been found that establish PM or ozone standards for the medium-term (2020-2025) or objectives for the longer term (2050), as Canada is seeking to do.

2.2 Canada's national air quality management framework

The actual setting of ambient air quality objectives in Canada is considered the dual responsibility of both the federal government and the provincial and territorial governments. However, air quality management in Canada is shared between federal, provincial, and regional or local authorities. This means that while provinces have the responsibility and authority to set and enforce air quality objectives, local and regional governments have the authority to pass bylaws that may restrict activities contributing to air pollution emissions in areas under their control. Moreover, the provincial governments have the authority to delegate primary responsibility for air quality management to regional or municipal jurisdictions. For example, in British Columbia, the provincial government delegated authority for air quality management to the Greater Vancouver Regional District (GVRD). In another example, the government of Quebec has delegated air quality management responsibilities to the Montreal Urban Community. But because air quality is of obvious local concern to residents, and even though many of the legislative and regulatory instruments are under both federal and provincial jurisdictions, Canada has typically pursued a shared and coordinated approach to setting ambient air quality standards.

2.2.1 National ambient air quality objectives

Historically, national ambient air quality objectives (NAAQOs) were first established by the federal government in 1969 under the Clean Air Act. In 1976, standards for ozone and PM were established under this act. In 1988, the Canadian Environmental Protection Act (CEPA) was passed into law, replacing the Clean Air Act. A federal/provincial advisory committee was established — the Working Group on Air Quality Objectives and Guidelines (WGAQOG) — which developed revised NAAQOs under CEPA. The committee's objectives were intended to represent national goals for outdoor air quality, to protect public health and the environment, and to ensure some degree of uniformity across the country.In 1999, the WGAQOG revised the PM objective and set a range of PM levels, rather than a specific value. Designed to ensure a substantial reduction in the risks to human health and the environment, the ranges are the following:

• 35 - 40 µg/m3 for PM10 (for particles < 10 µm diameter)
• 20 - 25 µg/m3 for PM2.5 (for particles < 2.5 µm diameter)

In 1999, when attempting to define a reference (baseline) level for ozone, the WGAQOG concluded that "most studies indicated a continuum of effects through all [the] ambient levels, with adverse effects below the Reference Level." In 1999, it stated that "substantial health benefits associated with reducing ozone concentrations may exist" at levels of 20 ppb and 25 ppb daily one-hour maxima.In 2000, CEPA was revised, introducing a new framework for setting ambient air quality objectives. This framework reflected the current state of knowledge regarding air quality parameters. It provided a uniform scale for assessing air quality that could guide governments in the risk management process, using such items as local standards and control strategies. It also advocated a continuous improvement approach for protection of the environment. In 2001, CEPA declared PM10 (less than or equal to 10 microns in diameter) a "toxic"6 substance. Ozone and its precursors (sulphur oxides, nitrogen oxides, volatile organic compounds, and gaseous ammonia) were subsequently added to the List of Toxic Substances, giving the federal government the authority to take action to reduce these substances in the environment.7 Once a substance is added to this list, the federal government works with the provinces, territories, industry, non-government organizations, and other interested parties to develop a management plan to reduce or eliminate the harmful effects of the substance on the environment and on the health of Canadians.

2.2.2 Canada-wide Standards

In January 1998, recognizing the need for a more collaborative national approach on standards setting, Canada's environment ministers, under the auspices of the Canadian Council of Ministers of the Environment (CCME), agreed to accept the Canada-wide Standards (CWS) process. This approach put in place a new national process for setting standards, guidelines, objectives, and criteria for the protection of the environment and human health. Standards for PM and ozone were among the first to be developed by the CCME for consideration (1999). The following standards were approved in 2000:

• The CWS for PM2.5 is 30 µg/m3 — a 24-hour average;
• The CWS for ozone is 65 ppb — an 8-hour average, with achievement based on the fourth-highest level measured annually over three years.

The target date for achievement of the standard was set for 2010. A system for monitoring and reporting on progress was put in place, as were special measures to take into account the transboundary flow of pollution from the United States and other countries. While these standards were initially intended to minimize exposure risks to human health and the environment, other considerations came into play in their development. Thus the final numbers had less to do with science and more to do with a negotiated settlement between the various jurisdictions. As a result, there is now perhaps too much flexibility, where provincial governments are able to adopt the CWS or not, or to use them as benchmarks for differing provincial standards that take into account their own priorities and circumstances. 7. For substances that are found to be toxic under CEPA 1999 and are added to the List of Toxic Substances in Schedule 1 of CEPA, Environment Canada and Health Canada must propose an instrument to establish preventive or control actions for managing the substance and, thereby, reduce or eliminate risks to human health and the environment posed by its use and/or release.