National Ambient Air Quality Objectives For Particulate Matter - Executive Summary

Sources

Particulate matter is a ubiquitous pollutant, reflecting the fact that it has both natural and anthropogenic sources. Natural sources of primary PM include windblown soil and mineral particles, volcanic dust, sea salt spray, biological material such as pollen, spores and bacteria, and debris from forest fires. By and large these natural sources produce coarse particles, although high temperature sources such as wildfires will generate fine PM. Secondary PM can be formed through reactions involving natural sources of the precursor gases. For example, volatile organic carbons (VOCs) are released from trees and nitrogen oxides are released from soils. Anthropogenic sources also produce both primary and secondary PM, and both coarse and fine particles. Windblown agricultural soil, and dust from roads, construction sites and quarrying operations, all contribute primarily to the coarse fraction. Smaller particles of more complex chemical composition are generated as a result of many industrial processes, and through fossil fuel combustion (electrical power plants, gasoline and diesel vehicles, industrial boilers, residential heating etc.), both directly and via the release of precursor gases (VOCs, SO₂ and NOx).

Current estimates of the magnitude of actual emission sources in Canada are restricted to primary PM and are thus incomplete. In 1990, an estimated 1.0 Mt of PM₁₀ was emitted from primary sources excluding open sources. Primary PM_2.5 accounted for approximately 75% of this total. The source sector breakdown for primary PM₁₀ emissions is as follows: 42% industrial sources, 28% forest fires, 15% non-industrial fuel combustion, 11% transportation and 2% each, incineration and miscellaneous sources. The corresponding breakdown for PM_2.5 emissions shows equally large (34%) contributions from forest fires and industrial sources, and smaller contributions from non-industrial fuel combustion (16%), transportation (13%), incineration (2%) and miscellaneous sources (1%). Sources considered in each category include the following:

industrial: coal industry, pulp and paper industry, non-ferrous mining and smelting, iron and steel production, wood industry and mining and quarrying;

non-industrial fuel combustion: commercial and residential fuel combustion, residential fuelwood combustion and electric power generation;

transportation: gasoline and diesel vehicles and trucks, propane powered vehicles, railroads, marine craft, aircraft and tire wear;

incineration: wood waste and other types of incineration;

miscellaneous sources: structural fires, pesticides and fertilizer application, cigarette smoking and the marine cargo handling industry.

These emission estimates exclude open sources such as paved and unpaved roads, construction sites and prescribed burning, from which estimates of particulate emissions are particularly difficult to obtain. Although primary PM emissions from these sources have not yet been adequately quantified, these sources are known to release substantial quantities of both fine and coarse PM, although releases are typically episodic in nature. Estimates of the magnitude of secondary particulate sources are required to complement the data on primary emissions; however, these can only be derived using mathematical models which take into account precursor gas emissions and the complex atmospheric chemistry involved in the formation of secondary PM. Such models are still in the development stage. Limited studies in the Lower Fraser Valley of British Columbia have indicated that secondary particulates may account for up to 50% of PM_2.5 during the summer months. Similarly high contributions may be expected in other urban areas of Canada.

The available data clearly indicate that source contributions vary from province-to-province and by region. In the Yukon and Northwest Territories, British Columbia and Saskatchewan, forest fires and/or prescribed burning are the largest estimated sources of PM₁₀. Industrial sources are a major contributor to provincial PM₁₀ emissions in all provinces except Prince Edward Island. In PEI, non-industrial fuel combustion (primarily residential wood combustion) is the major source. The transportation sector is also a large contributor in Ontario and BC, while non-industrial fuel combustion is significant in Alberta, Ontario, Québec and Nova Scotia. A further consideration is the seasonality of particulate emissions. Residential wood combustion is most prevalent during the winter months, while forest fires are generally limited to the summer months. Emissions from the industrial and transportation sectors occur year-round, although they are subject to many fluctuations.