Archived: Air Pollutant Emission Inventory report: chapter 5

Annex 1: Definitions of the air pollutants

This appendix provides definitions for the 17 air pollutants inventoried by the APEI and listed in Chapter 1. Examples of some major sources are also provided.

A1.1 Criteria air contaminants

Particulate Matter (PM)

PM consists of microscopic solid and liquid particles of various origins that remain suspended in air for any length of time. PM includes a broad range of chemical species, such as elemental carbon and organic carbon compounds, oxides of silicon, aluminium and iron, trace metals, sulphates, nitrates and ammonia (NH ₃). It is ubiquitous, being emitted from both natural and anthropogenic (human) sources. Emissions of fine PM (PM _2.5) and its precursor gases originate typically from combustion processes-- motor vehicles, industrial processes, vegetative burning and crop production.

Total Particulate Matter (TPM)

TPM includes any PM with a diameter less than 100 microns. ^Footnote4

Particulate Matter less than or equal to 10 Microns (PM ₁₀)

PM ₁₀ includes any PM with a diameter less than or equal to 10 microns. ^Footnote5

Particulate Matter less than or equal to 2.5 Microns (PM _2.5)

PM _2.5 includes any PM with a diameter less than or equal to 2.5 microns.

Sulphur oxides (SO _x)

Sulphur oxides (SO _x) are a family of gases that consist mostly of sulphur dioxide (SO ₂), a colourless gas. It can be chemically transformed into acidic pollutants, such as sulphuric acid and sulphates (sulphates are a major component of ambient fine particles). SO ₂ is generally a by-product of industrial processes and the burning of fossil fuels, with the main contributors being ore smelting, coal-fired power generators and natural gas processing. SO ₂ transformed to sulphuric acid is also the main ingredient of acid rain, which can damage crops, forests and ecosystems.

Nitrogen oxides (NO _x)

NO _x include nitrogen dioxide (NO ₂) and nitrogen oxide (NO); both are reported as NO ₂ equivalent. NO _x reacts photochemically with volatile organic compounds (VOCs) in the presence of sunlight to form ground-level ozone. It can also transform into ambient PM (nitrate particles) and is a component of acid rain. NO _x originate from both anthropogenic and natural sources. The main anthropogenic sources are mobile (on-road vehicles), electric power generation and the upstream petroleum industry, and the main natural sources are lightning and soil microbial activity.

Volatile organic compounds (VOCs)

VOCs are organic compounds containing one or more carbon atoms that evaporate readily to the atmosphere and react photochemically to form ground-level ozone. ^Footnote6 VOCs may condense in the atmosphere to contribute to ambient PM formation. Besides biogenic sources (e.g. vegetation), other major sources include the petroleum industry, mobile sources and solvent use. Some VOCs, such as formaldehyde and benzene, are carcinogenic.

Carbon monoxide (CO)

CO is a colourless, odourless, tasteless and poisonous gas. CO can have a significant impact on human health. When inhaled, it forms carboxyhemoglobin, a compound that inhibits the blood’s capacity to carry oxygen to organs and tissues. It also participates to a lesser degree in the formation of ground-level ozone. The principal human source of CO is incomplete combustion of hydrocarbon-based fuels and is emitted primarily from mobile sources (on-road vehicles). Other lesser but significant sources are the wood industry, residential wood heating and forest fires. Ambient CO concentrations are much higher in urban areas due to the number of human sources.

Ammonia (NH ₃)

Gaseous NH ₃, which originates from anthropogenic sources, has been identified as one of the principal precursors to PM _2.5. Major sources of NH ₃ emissions include agricultural fertilizer use, agricultural livestock and synthetic fertilizer manufacturing.

A1.2 Selected heavy metals

Lead (Pb)

Lead occurs naturally in the Earth’s crust. It is declared as a toxic substance under the Canadian Environmental Protection Act, 1999 (CEPA) and is used extensively in industry to manufacture products such as lead-acid batteries and radiation shields. Metals processing is the major source of Pb emissions to air, with the highest levels of Pb air emissions originating from the non-ferrous smelting and refining industry.

Cadmium (Cd)

Cadmium, declared as toxic under CEPA, is present in the air as a result of anthropogenic activities and natural processes. The largest anthropogenic source is metal production (particularly base-metal smelting and refining).

Mercury (Hg)

Mercury is declared as toxic under CEPA. Hg’s unique properties are utilized in various consumer products, such as fluorescent lights. When Hg is released to the atmosphere, it can be transported on wind currents, deposited onto land and re-emitted into the atmosphere several times.

A1.3 Persistent organic pollutants

Dioxins and furans

Dioxins and furans are a family of toxic compounds that vary widely in toxicity. Both dioxin and furan “congeners” are expressed in terms of toxic equivalents (TEQs) to the most-toxic form of dioxin: 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD). The largest source of dioxins and furans in Canada is the burning of municipal and medical waste. Other major sources include the production of iron and steel, backyard burning of household waste, and fuel combustion for transportation and home heating.

Polycyclic Aromatic Hydrocarbons (PAHs)

PAHs are a group of organic compounds emitted to the Canadian environment from natural and anthropogenic sources. Comprehensive air emissions information is available for the following four PAHs: benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene and indeno[1,2,3-cd]pyrene. National Pollutant Release Inventory (NPRI) facility-reported data are available for additional PAHs. The largest anthropogenic sources of PAHs released to the atmosphere are residential wood heating and aluminium smelters.

Hexachlorobenzene (HCB)

HCB is a persistent organic pollutant (POP) that is released in trace amounts as a by-product of the manufacture and use of chlorinated solvents and pesticides through long-range transport and deposition, incineration, and other industrial processes.

A1.4 References

Pirrone N, Cinnirella S, Feng X, Finkelman RB, Friedli HR, Leaner J, Mason R, Mukherjee AB, Stracher GB, and Streets DG. 2010. Global mercury emissions to the atmosphere from anthropogenic and natural sources (PDF Format 550 KB). Atmospheric Chemistry and Physics 10 (13):5951-64.

[UNEP] United Nations Environment Programme. 2013. Global Mercury Assessment 2013: Sources, Emissions, Releases and Environmental Transport (PDF Format 8.9 MB). Geneva, Switzerland: UNEP Chemicals Branch.