Canada’s Air Pollutant Emissions Inventory Report 2024: annex 1

Definitions of the Air Pollutants

This annex provides definitions for the 17 air pollutants inventoried by the Air Pollutant Emissions Inventory (APEI). These pollutants are identified in the Canadian Environmental Protection Act, 1999 (CEPA 1999) and the 1979 Convention on Long-Range Transboundary Air Pollution (CLRTAP) and associated protocols ratified by Canada. The APEI also reports some emissions of additional air pollutants not covered by protocols including ammonia (NH₃), carbon monoxide (CO), particulate matter less than or equal to 10 microns in diameter (PM₁₀) and total particulate matter (TPM) that impact air quality as well. Chapter 2 summarizes the air emissions of these air pollutants grouped into 12 families from various sectors.

A1.1 Criteria Air Contaminants

Particulate Matter (PM)

PM consists of microscopic airborne solid and liquid particles of various origins that remain suspended in air for any length of time. PM can be emitted directly into the atmosphere or formed secondarily from precursor gases as a result of physical and chemical transformations. 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 (NH₃). It is ubiquitous, being emitted from both natural and anthropogenic (human) sources. The size of PM particles influences the extent of environmental and health damage caused.

Total Particulate Matter (TPM)

TPM includes any airborne PM with a diameter less than 100 microns. It includes PM₁₀ and PM_2.5.

Particulate Matter Less Than or Equal to 10 Microns (PM₁₀)

PM₁₀ includes any airborne PM with a diameter less than or equal to 10 microns. It includes PM_2.5.

Particulate Matter Less Than or Equal to 2.5 Microns (PM_2.5)

PM_2.5 includes any airborne PM with a diameter less than or equal to 2.5 microns. Emissions of PM_2.5 and its precursor gases originate typically from combustion processes, such as motor vehicles and vegetation burning, but can also come from industrial processes and crop production.

Sulphur Oxides (SO_x)

SO_x are a family of gases that consist mostly of sulphur dioxide (SO₂), a colourless gas. It can be chemically transformed into acidic pollutants, such as sulphuric acid and sulphates (sulphates are a major component of ambient PM). SO₂ 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.

Both SO₂ in its untransformed state, and the acid and sulphate transformation products of SO₂, can have adverse effects on human health or the environment. SO₂ oxidation into sulphuric acid is the main ingredient of acid rain, which can damage crops, forests, buildings and materials, and contribute to acidification of ecosystems. When sulphate is combined with other compounds in the atmosphere, such as NH₃, it becomes an important contributor to PM_2.5. It is also one of the principal precursors to PM₁₀.

Nitrogen Oxides (NO_x)

NO_x include nitrogen dioxide (NO₂) and nitrogen oxide (NO). In this report, NO_x are reported as NO₂ equivalent. NO emitted during combustion quickly oxidizes to NO₂ in the atmosphere. NO₂ dissolves in water vapour in the air to form acids, and interacts with other gases and particles in the air to form particles known as nitrates and other products that may be harmful to respiratory systems of humans and their environment. Nitric acid (HNO₃) can cause damage to vegetation, buildings and materials, and contribute to acidification of ecosystems. NO_x reacts photochemically with volatile organic compounds (VOCs) in the presence of sunlight to form ground-level ozone. It can transform into ambient PM (nitrate particles) and is a component of acid rain. When nitrate is combined with other compounds in the atmosphere, such as NH₃, it also becomes an important contributor to the formation of PM_2.5. NO_x originate from both anthropogenic and natural sources. The main anthropogenic sources are from combustion in transportation, electric power generation as well as the upstream oil and gas industry. The main natural sources are forest fires, lightning and soil microbial activity.

Volatile Organic Compounds (VOCs)

VOCs are gases or vapors organic compounds containing one or more carbon atoms that evaporate readily to the atmosphere and react photochemically to form ground-level ozone, and PM_2.5, leading to smog. VOCs originate from anthropogenic and natural sources. Besides biogenic sources (e.g., vegetation), other major sources include combustion and evaporation processes related to the upstream oil and gas industry, general solvent use, mobile sources, and other miscellaneous sources.^{Footnote 1}  VOCs may condense in the atmosphere, contributing to ambient PM formation and acid rain. A number of individual VOCs, such as benzene and dichloromethane, have been assessed to be toxic under CEPA 1999, while other VOCs (e.g., formaldehyde and benzene) are carcinogenic. The term Non-methane volatile organic compounds (NMVOCs) is equivalent to VOCs in this report.

Carbon Monoxide (CO)

CO is a colourless, odourless, and tasteless poisonous gas that, when inhaled, reduces the body’s ability to use oxygen. It participates to a small degree in the formation of ground-level ozone. The principal human source of CO is incomplete combustion of hydrocarbon-based fuels, primarily from mobile sources. The wood industry, residential wood heating, and forest fires represent lesser but significant sources. Ambient CO concentrations are much higher in urban areas due to the larger number of human sources.

Ammonia (NH₃)

NH₃ is a colourless and corrosive gas that originates mostly from anthropogenic sources. Major sources of NH₃ emissions include agricultural livestock, waste management, agricultural fertilizer use and synthetic fertilizer manufacturing. NH₃ has been identified as one of the principal precursors to PM_2.5.

A1.2 Selected Heavy Metals

Lead (Pb)

Pb is a toxic metallic element, which occurs naturally in the Earth’s crust. Pb is used in plumbing, gasoline, paint, and pewter manufacturing. It 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. Small amounts of lead can be hazardous to human health.

Cadmium (Cd)

Cd 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), stationary fuel combustion, transportation, solid waste disposal, and sewage sludge application. Major sources from natural processes include weathering and erosion of cadmium-bearing rocks, as well as forest fires and volcanic emissions.

Mercury (Hg)

Despite its toxic nature, Hg has unique properties utilized to produce 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. Emissions of Hg in the atmosphere come from various sectors such as iron and steel production, electric power generation from combustion of coal, waste incineration and various commercial, residential and institutional uses. Hg can exist in several forms depending on the surrounding conditions.

A1.3 Persistent Organic Pollutants

Dioxins and Furans

Dioxins and furans are a family of anthropogenic toxic compounds that are found in very small amounts in the environment, including air, water, and soil. 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 sources of dioxins and furans in Canada are the burning of municipal and residential waste. Other major sources include the production of cement and concrete industry, the production of iron and steel, electrical power generation and home firewood burning. Natural sources of dioxins and furans are forest fire and volcanic eruptions.

Polycyclic Aromatic Hydrocarbons (PAHs)

PAHs are a group of organic compounds emitted to the environment from natural and anthropogenic sources. Some PAHs are genotoxic and induce mutations that initiate cancer. The largest anthropogenic sources of PAHs released to the atmosphere are home firewood burning, aluminum smelters and transportation. Forest fires are the most important natural source of PAHs in Canada.

In this report, 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. The National Pollutant Release Inventory (NPRI) facility-reported data are available for additional information on PAHs.

Hexachlorobenzene (HCB)

HCB is carcinogenic. It has not been used commercially in Canada since 1972 (Environment and Climate Change Canada [ECCC], 2017), although it is released to the environment in trace amounts as a by-product from the manufacture and use of chlorinated solvents and pesticides, through long-range transport and deposition. HCB has been prohibited globally under the Stockholm Convention and the Protocol on Persistent Organic Pollutants under the CLRTAP. The largest sources of emissions are from residential waste burning, iron and steel production, and non-ferrous refining and smelting.

References, Annex 1, Definitions of the air pollutants

[ECCC] Environment and Climate Change Canada. 2017. Toxic substances list: hexachlorobenzene [last updated 2017 April 05].