Outdoor Air Pollution Profile


IARC Monograph Vol. 109, 2016 (Group 1)

Outdoor Air Pollution Profile


  • A mixture of pollutants formed during various natural and anthropogenic processes
  • Associated cancer: Lung cancer
  • Main route of exposure: Inhalation
  • Primary sources: Transportation, power generation, industrial activity, heating, cooking, fuel or coal combustion, forest fires, volcanoes, and dust storms
  • Environmental exposures: Via combustion sources in outdoor air (and infiltration to indoor environments), such as industrial processes, vehicle exhaust, fireplaces, and forest fires
  • Fast fact: Particulate matter in outdoor air pollution is classified according to its size; smaller particles can penetrate deeper in airways than larger particles.

General Information

Outdoor air pollution is a mixture of gases and particulate matter (a complex mixture of solid particles and liquid droplets). Outdoor air pollutants are formed during natural and anthropogenic processes.[1] The most common anthropogenic sources are transport, power generation, industrial activity, heating, cooking, and fuel or coal combustion.[1] Natural sources include forest fires, volcanoes, and dust storms.[1]

The composition of outdoor air pollutants may vary considerably over time and space due to variations in the pollutants’ sources, as well as changes in weather and atmospheric transformations.[2] Major gaseous pollutants include sulfur dioxide, nitrogen oxides, and carbon monoxide. Major particulate matter components include organic and elemental carbon compounds, metal oxides, lead, and others.[2] The overall composition of outdoor air pollution in an environment is difficult to characterize due to the numerous pollutants that comprise it. However, particulate matter is typically classified according to its size. Suspended particulates tend to be less than 40 µm in diameter.[3] Particulates may be referred to as PM10 (all particles sized 10 µm or less), PM2.5 (all particles sized 2.5 µm or less), or TPM (total particulate matter).[4] Particulates can also be broken down into four main categories:

  • Ultra fine – less than 0.1 µm in diameter
  • Fine or respirable fraction – less than 2.5 µm in diameter
  • Coarse or inhalable fraction – between 2.5 to 10 µm in diameter
  • Total suspended particulates (TSP) – particles less than 40 µm in diameter

Each category of particles originates from different sources and interacts uniquely in the environment. For example, ultrafine particles are formed directly in combustion exhaust, mainly as hot vapours are condensed,[3] and can aggregate and coagulate over time to form fine particulates.[4] In contrast, particles in the fine fraction are produced mainly by combustion processes and by atmospheric reactions between precursor gases such as sulphur dioxide, nitrogen oxides, ammonia, and some volatile organic compounds.[3,4]

In 2013, the International Agency for Research on Cancer (IARC) evaluated the carcinogenic effects of outdoor air pollution and particulate matter associated with outdoor air pollution. The IARC assessment focused on pollutants released as a result of anthropogenic activities, especially combustion and industrial processes. IARC classified outdoor air pollution and particulate matter associated with outdoor air pollution as Group 1, carcinogenic to humans.[2] This classification is based on sufficient evidence of an association between exposure and lung cancer in humans, and limited evidence that exposure causes bladder cancer. There was sufficient evidence supporting the carcinogenicity of various components of outdoor air pollutants (whole diesel engine exhaust, diesel engine exhaust particles, extracts of diesel engine exhaust particles, condensates of gasoline engine exhaust, extracts from coal-derived soot and wood smoke, and emissions from combustion of coal and wood) in animal studies. Finally, there was strong mechanistic evidence that outdoor air pollution (and associated particulate matter) has genotoxic effects.[2]

Outdoor air pollution is associated with other health effects including chronic obstructive pulmonary disease, stroke, ischemic heart disease, and acute lower respiratory infection.[5]

Regulations and Guidelines

Occupational Exposure Limits (OEL)

Outdoor air pollution is not regulated as an occupational exposure.

Canadian agencies/organizations

Agency Designation/Position Year
CEPA PM10 and PM2.5:
Schedule 1, paragraph ‘c’
CEPA Emissions of particulate matter from copper and zinc smelter operations:
Schedule 1, paragraphs ‘a’ and’c’
CEPA = Canadian Environmental Protection Act

Air quality guidelines

Canadian Jurisdictions Level of PM10 (µg/m3) Notes
Canadian Reference Level(a) 25 24 hour average
BC Air Quality Objective[7] 50 24 hour average
ON Ambient Air Quality Criteria[8](b) 50 24 hour average
Canadian Jurisdictions Level of PM2.5 (µg/m3) Notes
Canadian Reference Level 15 24 hour average
Canada-Wide Standard(c) 27 24 hour average
Canada-Wide Standard(e) 8.8 Annual average
AB Air Quality Objective[9] 80
1 hour average
24 hour average
BC Air Quality Objective(d) 25 24 hour average
BC Air Quality Objective 8 Annual average
BC Planning Goal 6 Annual average
ON Air Quality Criteria 27
24 hour average
Annual average
Other Jurisdictions Level (µg/m3) Notes
US EPA[10](f) 150 PM10; 24 hour average
US EPA[10](g) 35 PM2.5; 24 hour average
US EPA[10](h) 12.5 PM2.5; annual average
WHO[11] 50 PM10; 24 hour average
WHO 20 PM10; annual average
WHO 25 PM2.5; 24 hour average
WHO 10 PM2.5; annual average
µg/m3 = micrograms per cubic metre
(a) Reference Level is defined as the level above which effects on human health and the environment can be demonstrated[12]
(b) Interim AAQC provided as a guide for decision making
(c) Attainment based on average of 98th percentile ambient measurement over 3 consecutive years[13]
(d) Achievement based on annual 98th percentile value
(e) The 3-year average of the annual average concentrations[13]
US EPA = United States Environmental Protection Agency
(f) Not to be exceeded more than once per year on average over three years
(g) To attain this standard, the 3-year average of the 98th percentile of 24-hour concentrations at each population-oriented monitor within an area must not exceed 35 µg/m3 (effective December 17, 2006)
(h) To attain this standard, the 3-year average of the weighted annual mean PM2.5 concentrations from single or multiple community-oriented monitors must not exceed 15 µg/m3
WHO = World Health Organization

Environmental Exposures Overview

Canadians are exposed to fine and ultrafine particles by breathing outdoor air containing emissions from any combustion source, including industrial processes, gasoline and diesel engine exhausts, fireplaces, furnaces, prescribed burning for forestry and agricultural purposes, and naturally-caused wildfires.[14]

CAREX Canada estimates of potential lifetime excess cancer risk for outdoor air pollution are unavailable at this time. According to the Canadian Population Attributable Risk of Cancer (ComPARe) study, 6.9%, or 1,700 lung cancer cases were due to exposure to PM2.5 in outdoor air in 2015[15]. The study estimates that over 3,000 lung cancer cases could be prevented between 2016 and 2042 if declining trends in PM2.5 continue.

Particulates in outdoor air are monitored by the National Air Pollution Surveillance (NAPS) network. In 2013, the annual average levels of PM2.5 was 7.3 µg/m3, and the annual peak 24-hour concentration was 20 µg/m3. Both of these values remained below the 2015 Canada Wide Standard.[14] Between 1985 and 2012, daily averages for PM10 remained below 10 µg/m3 in 44 of 49 different sites located across Canada. Higher levels of PM10 were found in large urban areas and near roadways.[16]

A search of Environment Canada’s National Pollutant Release Inventory (NPRI) yielded the following results on current potential for exposure to outdoor air pollution in Canada:

NPRI reported releases

NPRI 2015[17]
Substance name: ‘PM – Total Particulate Matter’
‘PM10 – Particulate Matter ≤ 10 microns’
‘PM2.5 – Particulate Matter ≤ 2.5 microns’
All amounts released into environment (on-site release)
PM Type # of facilities Quantity Industry
Total PM 1,188 327,251 t Resource extraction and processing, manufacturing
PM10 3,142 131,212 t
PM2.5 3,521 48,780 t
t = tonne

For more information, see the environmental exposures tab for outdoor air pollution.


1. Unger N, Bond TC, Wang JS, Koch DM, Menon S, Shindell DT et al. “Attribution of climate forcing to economic sectors“. Proceedings of the National Academy of Sciences 2010;107(8):3382–3387.
2. International Agency on Research for Cancer (IARC). IARC Monographs. Outdoor Air Pollution: Volume 109 (2016)
4. Brauer M. “Sources, Emissions, Concentrations, Exposures and Doses.’ A Citizen’s Guide to Air Pollution” David Suzuki Foundation, Vancouver, B.C. 2002;2
7. Government of British Columbia. British Columbia Ambient Air Quality Objectives (2018) (PDF)
8. Ontario Ministry of the Environment and Climate Change. Ontario’s Ambient Air Quality Criteria (2016)
9. Alberta Environment and Parks. Ambient Air Quality Objectives (2019)
10. US Environmental Protection Agency (EPA). Criteria Air Pollutants – NAAQS Table (2020)
11. World Health Organization (WHO). Air Quality Guidelines – Global Update 2005 (2006) (PDF)
13. CCME. CAAQs (2022)
14. CCME. Air Quality Report (2022)
15. Gogna P, Narain TA, O’Sullivan DE, Villeneuve PJ, Demers PA, Hystad P, Brenner DR, Friedenreich CM, King WD; ComPARe Study Team. “Estimates of the current and future burden of lung cancer attributable to PM2.5 in Canada“. Prev Med 2019; 122:91-99.
17. Environment and Climate Change Canada. National Pollutant Release Inventory (NPRI) Facility Search (Substance name: ‘Particulate matter’)


Other Resources

  1. Environment and Climate Change Canada. National Air Pollution Surveillance (NAPS) Program (2022)

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