Canada’s Air Pollutant Emissions Inventory Report 2020: annex 1
Definitions of the air pollutants
This annex provides definitions for the 17 air pollutants inventoried by the Air Pollutant Emissions Inventory (APEI). Chapter 2 summarizes the air emissions of these air pollutants from various sectors.
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 (NH3). It is ubiquitous, being emitted from both natural and anthropogenic (human) sources. Emissions of fine PM (PM2.5) 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.Footnote 1
Particulate matter less than or equal to 10 microns (PM10)
PM10 includes any PM with a diameter less than or equal to 10 microns.Footnote 2
Particulate matter less than or equal to 2.5 microns (PM2.5)
PM2.5 includes any PM with a diameter less than or equal to 2.5 microns.
Sulphur oxides (SOx)
SOx 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 fine particles). 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. SO2 transformed to sulphuric acid is the main ingredient of acid rain, which can damage crops, forests and ecosystems.
Nitrogen oxides (NOx)
NOx include nitrogen dioxide (NO2) and nitrogen oxide (NO), both of which are reported as NO2 equivalent. NOx 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. NOx originate from both anthropogenic and natural sources. The main anthropogenic sources are transport and mobile equipment as well as the upstream oil and gas 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.Footnote 3 VOCs may condense in the atmosphere to contribute to ambient PM formation. Besides biogenic sources (e.g. vegetation), other major sources include the upstream oil and gas industry, general solvent use, and mobile sources. Some VOCs, such as formaldehyde and benzene, are carcinogenic.
Carbon monoxide (CO)
CO is an odourless 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 combustion, primarily from mobile sources (on-road vehicles). Ambient CO concentrations are much higher in urban areas due to the larger number of human sources.
Gaseous NH3, which originates from anthropogenic sources, has been identified as one of the principal precursors to PM2.5. Major sources of NH3 emissions include agricultural livestock, agricultural fertilizer use and synthetic fertilizer manufacturing.
A1.2 Selected heavy metals
Pb occurs naturally in the Earth’s crust. It is declared toxic 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.
Cd, declared 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).
Hg is declared toxic under CEPA. Its unique properties are 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.
A1.3 Persistent organic compounds
Dioxins and furans (D/F)
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 sources of dioxins and furans in Canada are the burning of residential waste as well as marine transportation. Other major sources include the production of cement and concrete industry, the production of iron and steel, and home firewood burning.
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 home firewood burning as well as transportation and mobile equipment sources.
HCB is a persistent organic pollutant where the largest sources of emissions are from residential waste burning, iron and steel production, and non-ferrous refining and smelting.
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