The State of Canada's Environment — 1996 Chapter 10 — Environmental Conditions and Trends Atmosphere Local air quality Suspended particles

Suspended particles

Unlike ozone, particulate matter may be found in high concentrations in the air at any time of year. Much of it comes from natural sources such as windblown dust, pollen, soot from forest fires, and sea salt. However, human activities such as transportation, agriculture, mining, smelting, metal processing, construction, and pulp and paper processing can add considerably to natural concentrations.

Anthropogenic airborne particulates that are less than 10 µm in diameter (a micrometre is one-thousandth of a millimetre) are primarily a consequence of industrial processes and motor vehicle use. These are the particles of greatest concern because of the hazard they pose to human health. They are easily inhaled and can irritate the respiratory tract, thereby aggravating existing conditions such as asthma and cardiopulmonary disease. In 1994, the World Health Organization ceased recommending a threshold level for airborne particles because no specific concentration represented an apparent threshold (WHO 1994). Rather, recent data suggest a continuum of effects, rising with exposure. Increased concentrations of particles in the air are associated with higher risk of mortality as a result of respiratory and cardiac disease and lung cancer. Health effects associated with a rise in particle concentrations include increases in hospitalizations and visits to emergency wards for respiratory problems, increases in the number of days of restricted activities among adults and school absenteeism among children, increases in the number of symptoms of respiratory disease, and minor reduction of respiratory functions (Vedal 1995).

In a survey of Ontario sites in 1992, inhalable particles constituted 38–61% of total suspended particulates (OMEE 1993). Particles in this size range also contribute substantially to haze and the associated degradation of visibility in urban areas. The smallest inhalable particles, those less than 2.5 µm in diameter, are of special concern because they may contain a wide range of toxic metals and chemicals as well as acid-forming sulphates and nitrates.

Human-induced particulate pollution occurs primarily in larger cities, where industries, motor vehicles, heating plants, and residential furnaces provide many emission sources. Smaller centres and rural areas may also experience unacceptable levels of particulate pollution as a result of emissions from industrial sources such as pulp mills or smelters or as a consequence of other activities such as transportation, agriculture, and forestry. In British Columbia, Yukon, Quebec, and the Atlantic provinces, wood smoke from the burning of logging or sawmill waste and from the use of wood for home heating is a common source of pollution (Haliniak and Schwartzel 1992). In these areas, particulate pollution sometimes occurs in winter because of increased heating demands and the more frequent formation of temperature inversions, beneath which contaminants are confined.

Particulate pollution is a seasonal problem in the Arctic. Known as Arctic haze, it occurs in winter and early spring, when conditions favour the transport of contaminants to, and their retention in, the Arctic atmosphere. These contaminants originate primarily in the industrial regions of Asia, Europe and North America and are transported poleward by prevailing winds. Once the contaminants reach the Arctic, factors such as lack of sunlight, cold, stable air, and low precipitation combine to prolong their atmospheric lifetime (Barrie et al. 1992; see also Chapter 9 for further discussion of Arctic haze).

Industrial pollution controls, paving of dirt roads, improvements in energy efficiency, cleaner burner technologies, and increased use of cleaner-burning fuels such as natural gas have helped to reduce particulate emissions over the last 20–25 years ( Fig. 10.3). In fact, the NAAQOs for particulates were exceeded fewer times between 1990 and 1992 than over the previous decade (see Chapter 12, Fig. 12.9), although economic recession and the cool, wet summer of 1992 in eastern North America likely share some of the credit for this improvement.

Figure 10.3 Particulate emissions by source, 1970–1990

Further reductions in particulate emissions can be expected to result from other pollution control initiatives such as the NOx/VOC management plan and energy efficiency measures contained in the National Action Program on Climate Change (see Chapter 15). Significant emission reductions are being achieved by industry working cooperatively with governments. In addition, many communities have instituted "no burn" days or other restrictions to limit wood smoke emissions when weather conditions are unfavourable (B.C. Ministry of Environment, Lands and Parks and Environment Canada 1993).