Skip Ribbon Commands
Skip to main content
Traffic-related air pollution
Navigation help: Hover over this icon   
Printing help: Hover over this icon       



Overall air quality in Ontario has improved in recent years, but traffic remains a major contributor to air pollution. As many Ontarians spend time close to major roadways, they are at risk of increased exposure to traffic-related air pollution (TRAP) and its associated health impacts. Better understanding of population-level TRAP exposure can focus efforts on reducing the specific health burden due to this issue.

Highlights

Concentrations of air pollutants associated with traffic decreased in Ontario from 2004 to 2013. These improvements were greater near roads than in Ontario overall, and may reflect improved emission standards for vehicles.

Over one-quarter (27.8%) of Ontarians live within 100 metres (m) of a major road or within 500 m of a highway, leaving them at greater risk of adverse health effects associated with TRAP.

Many schools (26.3%) and long-term care facilities (48.4%) in Ontario are located in TRAP-exposed areas, putting vulnerable populations–children, older adults and people with pre-existing health conditions–at risk.

Ontarians who commute for long periods along major roads, whether on foot, bicycle or in a vehicle, are exposed to high TRAP concentrations. Over 40% of Ontarians commute 30 minutes or more to work, including 11.2% who commute more than an hour.

Exposure to TRAP can be decreased through traffic reduction strategies, improved emissions standards and land-use planning policies that maintain a buffer between major roads and buildings with vulnerable populations, such as schools and long-term care facilities.

Size of the problem

Air quality in Ontario is generally good compared to other areas around the world (1,2). Concentrations of air pollutants can vary widely within a geographical area, however, and people who live near major roads and traffic corridors can be exposed to higher levels of traffic-related air pollution (TRAP) (3,4). Traffic is a major contributor to air pollution in Ontario, not only in urban areas, but also in rural areas (5) where major roads and highways often have greater proportions of diesel vehicles that contribute to high pollution levels (6).

Living in TRAP-exposed areas–within 100 m of a major road or within 500 m of a highway–may increase an individual's risk of health problems (7). Specifically exposure within 300 m to 500 m of a major road causes the onset (1)and worsening (7) of asthma in children. Exposure to TRAP has been associated with other health outcomes however the evidence is not yet strong enough to confirm that TRAP is the cause of these outcomes (1,7). In Canada, approximately one third of the population live in TRAP-exposed areas (1,2). Similarly, in Ontario over one-quarter (27.8 %) of the population lived in TRAP-exposed areas in 2011 (the most recent year available). In the same year 23.1% of people in Ontario actually lived closer–within 100 m of a major road or within 150 m of a highway and 11.7% lived within 50 m of a major road or highway. The proportion of the population residing in TRAP-exposed areas varied across the 36 public health units (PHUs) in Ontario, ranging from 11.8% to 43.8%. The six health units that exceeded the provincial estimate were all in southern Ontario and were of a variety of urban/rural population mixes.

Figure 1: Percent of the population exposed to TRAP by public health unit, Ontario, 2011

Buffer

Hover over the magnifying glass information about air and definitions of "major road" and "highway"



Data source:  1) Statistics Canada. Geographic attribute file: census year 2011. Ottawa, ON: Minister of Industry; 2012. Date extracted: 2015 Jun 1. Available from: http://www12.statcan.gc.ca/census-recensement/2011/geo/ref/att-eng.cfm 2) Ontario. Ministry of Natural Resources and Forestry; Land Information Ontario. Ontario Road Network File: Road Net Element. Toronto, ON: Queen's Printer for Ontario; n.d. Date extracted: 2012 Oct 25.




Exposure

Concentrations of some air pollutants, notably ultrafine particles (UFP) and nitrogen oxides (e.g., NO, NO2), are highest closer to major roads and highways (7). Different traffic-related air pollutants disperse at different rates (10). Concentrations of primary pollutants such as NO and UFP, which are emitted directly into the air from vehicles, decrease rapidly with increasing distance from roads. In comparison, the concentrations of secondary pollutants such as NO2 and particulate matter (PM2.5), which form in the atmosphere when primary pollutants react, decrease more gradually with increasing distance from major roadways (1,7,10). The concentrations of some traffic-related air pollutants decrease by over 50% within the first 150 m from the roadway and are generally at background levels (i.e., concentrations measured at air monitoring stations away from traffic) by 500 m from the roadway (Figure 2) (10).

Distance from the road is not the only factor affecting TRAP concentrations: traffic-related factors, meteorology, the built environment and topography also have an effect (1,7). Traffic-related factors include traffic speed, traffic volume and the proportion of older vehicles and heavy-duty vehicles, such as trucks and buses on the roadway (1). Trucks and buses that use diesel fuels release much higher amounts of particulate matter per distance travelled compared to light-duty gasoline vehicles such as cars (1). Meteorological factors include wind direction, wind speed, precipitation and solar radiation. For example, air pollution levels upwind of roads decrease much faster compared to levels downwind. Built environment factors include the presence of 'street canyons'–streets with tall buildings in continuous rows alongside them. Street canyons prevent the dispersal of TRAP, resulting in higher concentrations of pollutants along roads (1). Topographical factors include land surface characteristics, such as whether roads are surrounded by open land or ridges.


Figure 2: Relative concentration of air pollutants


Data source: Karner AA, Eisinger DS, Niemeier DA. Near-roadway air quality: synthesizing the findings from real-world data. Environ Sci Technol. 2010;44(14):5334-44.

 

Trends

From 2004 to 2013, the average annual concentrations of NO, NO2, NOx, and PM2.5, pollutants which are associated with traffic, decreased throughout Ontario. Decreases in air pollutant concentrations are thought to be related to reductions in emissions from both mobile sources (i.e., vehicles) and stationary sources (e.g., industrial facilities) within Ontario (5), and to reductions in pollutants from parts of the United States upwind from Ontario.

Ontario has a network of 40 air quality monitoring stations, some situated closer to major roads or highways than others (5). A comparison of the concentrations of primary air pollutant NO and NOx (consisting of a mixture of NO and the secondary pollutant NO2) at two southern Ontario air quality monitoring stations found that the concentrations decreased more rapidly at a monitor located in a traffic-dense area (Toronto West) compared to a monitor located far from traffic (Brantford) and to concentrations averaged across all monitoring stations in Ontario. The pattern of decrease of secondary pollutants PM2.5 and NO2 was similar for Toronto West, Brantford, and Ontario overall (Figure 3). The levels of these pollutants measured at monitors near roads likely reflect reductions in emissions from traffic (1), which may explain the rapid decrease in NO, a primary pollutant. In contrast, patterns of decrease of secondary pollutants PM2.5 and NO2 near roads more closely follow the general decline in overall air pollutant levels.

Despite improvements in overall air quality, Ontarians who spend large amounts of time on or near major roads and highways remain at risk of high exposure to TRAP. Increasing urbanization in Ontario (11) and worsening traffic could result in a greater percentage of the population being exposed to high levels of TRAP (1,12).

Figure 3: NO NO2 NOx PM2.5 concentration by pollution monitoring station location, Ontario, 2004–20122013

Select pollution monitoring station to include
Select pollution monitoring station to highlight
Select a pollutant
Hover over the magnifying glass for information about air pollution monitoring.

Data source: Ontario. Ministry of the Environment and Climate Change. Air quality in Ontario 2013 report [Internet]. Toronto, ON: Queen's Printer for Ontario; 2015 [cited 2015 Dec 29]. Available from: http://www.airqualityontario.com/downloads/AirQualityInOntarioReportAndAppendix2013.pdf

 

Populations at risk

Children, seniors, and people with pre-existing health conditions are more vulnerable to adverse health effects related to TRAP exposure, and people with socioeconomic status (SES)–that is lower incomes and education–may be exposed to higher levels of TRAP.

Children are more vulnerable to air pollution because of their anatomical and physiological characteristics such as narrow airways, developing lungs and immune systems, and higher breathing rates. Children often spend more time than adults do being physically active outdoors which may increase their exposure to air pollution (14). Children may also experience increased exposure during the commute to, and while at, school (14). Schools located near major roads and highways have been found to have greater concentrations of air pollutants indoors and outdoors (14). In Ontario, 26.3% of publicly-funded elementary schools are located in TRAP-exposed areas, representing 22.6% of children enrolled in public schools. The proportion of public elementary schools in TRAP-exposed areas varies from 11.4% to 48.9% across public health units, representing 9.6% to 47.7% of children enrolled in public schools (Figure 4).

Compared to the general population, seniors exposed to air pollution are at greater risk of illness and death, mainly from cardiovascular and respiratory diseases (15,16), particularly people with pre-existing health conditions. In Ontario, 48.4% of long-term care homes are located near major roads and highways, varying from 11.1% to 88.9% by PHU (Figure 4).

People with lower socioeconomic status (SES) may be exposed to greater levels of TRAP as they are more likely to live or attend school closer to major roads and highways (17). This evidence comes from the United States. Further studies are required to investigate whether this association also exists in Ontario.


Figure 4: Per cent of elementary schools (2015)/elementary school children (2013–14 school year)/long term care homes (2015) in high traffic areas in {{vis4GeoSelect}}

Buffer

Select a geography (Ontario or by public health unit)

Data sources: 1) Ontario. Ministry of Education; Ontario School Information System (OnSIS). Enrolment by grade in elementary schools: 2013-14 academic year. Toronto, ON: Queen's Printer for Ontario; 2014[updated 2015 Oct 8]. Date extracted: 2014 Nov 20. Contains information licensed under the Open Government License - Ontario. Available from: https://www.ontario.ca/data/enrolment-grade-elementary-schools2)Ontario. Ministry of Education; Board School Identification Database (BSID) / Ontario School Information System (OnSIS). Ontario public school contact information. Toronto, ON: Queen's Printer for Ontario; 2013[updated 2015 Oct 22]. Date extracted: 2015 Nov 20. Contains information licensed under the Open Government License – Ontario. Available from: https://www.ontario.ca/data/ontario-public-school-contact-information3) Ontario Agency for Health Protection and Promotion (Public Health Ontario). Stakeholder relationship management (SRM) system. Toronto, ON: Queen's Printer for Ontario. Date extracted: 2015 Feb 19 4) Ontario. Ministry of Natural Resources and Forestry; Land Information Ontario. Ontario Road Network File: Road Net Element. Toronto, ON: Queen's Printer for Ontario; n.d. Date extracted: 2012 Oct 25.










Commuting

People who commute on or near major roads are at risk of greater exposure to TRAP than people who do not. The concentrations of major air pollutants such as PM2.5 and NO2 on major roads and in vehicles are often significantly higher than concentrations measured at air monitoring stations away from traffic (7,18). In-vehicle concentrations were found to be similar to on-road concentrations, indicating that vehicles do not provide much protection against air pollution (7,18). For example, in Canadian cities, in-vehicle concentrations of NO2 and PM2.5 were found to be 260% and 63% higher, respectively, than the average concentrations of these pollutants measured at air monitoring stations in each city (18). High concentrations of TRAP also present a hazard for cyclists and pedestrians who travel along major roads. Increased breathing rate and depth for cyclists (19) and fast walkers can contribute to higher exposure levels.

The time spent commuting on or near major roads is therefore a determinant of exposure to TRAP. In 2011, the average commute time for Ontarians who worked outside the home was 27.6 minutes each way, with 42.1% commuting over 30 minutes, including 11.2% commuting one hour or more each way. Commute times varied by PHU, with people commuting for one hour or more ranging from 2.4% to 20.8% of the population. Commute times were longer in urban PHUs, particularly in the Greater Toronto Hamilton Area. Commute times also varied by mode of transportation. Of people who took public transit, 32.9% commuted one hour or more (average time 45.7 minutes), compared to 8.2% of people who travelled by car, truck or van (average time 25.5 minutes), and 1.1% of people who walked (average time of 13.6 minutes) (Figure 5).

Figure 5: Commute time to work by {{vis5ModeRadio}}, (age 15+), {{vis5GeoSelect}}, 2011

Select a commuting mode

Select a geography (Ontario or by public health unit)

Data sources: Statistics Canada, Advisory Services, Central Region. Semi-custom table specifications. Database: 2011 National Household Survey (NHS). Geography: 1) Canada, provinces, territories and health regions (approximately 149 geographies) 2) Census metropolitan areas, tracted census agglomerations and census tracts in Ontario (approximately 2361 geographies) (all GNRs included) [unpublished]. Prepared 2015 Jun 30.










Health Impacts

Exposure to outdoor air pollution has been associated with illness and death due to cardiovascular and respiratory disease (20,21). Outdoor air pollution (8) and diesel exhaust (8,22) have also been classified as cancer-causing in humans. Research evidence increasingly supports the relationship between TRAP exposure and poor health outcomes. Exposure to TRAP has been shown to cause the onset (1) and worsening (7) of asthma in children (Figure 6). Exposure to TRAP has been associated with other health outcomes such as all-cause mortality (7), cardiovascular mortality (7), cardiovascular disease (7) , respiratory symptoms in adults (7) , decreased lung function in people of all ages (7), onset of asthma in adults (1) and lung cancer (1), however the evidence supporting these associations is not yet at the point where TRAP exposure can be confirmed as the cause of these health outcomes (Figure 6). Further research using near-road monitoring networks will help to improve understanding of linkages between TRAP and health outcomes (13).



Figure 6: Summary of the strength of evidence between exposure to TRAP and health outcomes




Hover over the magnifying glass for information on literature review.

Importance

Public health has a key role to raise awareness about the health risks associated with outdoor air quality, and working with partners, to identify strategies such as developing policies at the local and provincial levels that reduce exposure to environmental health hazards.

Health effects due to locally elevated traffic emissions have been identified (1,7). Reducing population exposure to TRAP can be accomplished through long-term strategies such as encouraging land-use planning that incorporates a setback, or buffer zone, between major traffic arteries and residential and institutional construction, especially buildings such as daycares, schools and long-term care facilities. This strategy has been used in California, where schools must be built over 150 m from a major road (1). Reducing overall emissions by reducing motor vehicle use and making improvements to vehicular emission standards may also reduce exposures (5).

At the local level, mitigation strategies can focus on informing the public–especially vulnerable populations–about health risks associated with TRAP, encouraging physical activity away from major roads (1) and building active transportation infrastructure, such as bike lanes, away from busier roads (1). As diesel-fuelled vehicles contribute disproportionately to TRAP, limiting these vehicles to particular routes and times of day has also been used as a strategy to reduce exposure to TRAP in cities (1). As added benefits, many strategies to reduce TRAP may also assist to reduce greenhouse gas emissions, noise pollution and stress, improve safety for pedestrians and cyclists and promote physical activity (1).

References

  1. Brauer M, Reynold C, Hystad P; University of British Colombia School of Population and Public Health. Traffic-related air pollution and health: a Canadian perspective on scientific evidence and potential exposure-mitigation strategies [Internet]. Ottawa, ON: Health Canada; 2012 [cited 2015 Dec 29]. Available from: http://allergen-nce.ca/wp-content/uploads/pubs/Traffic&Health.pdf
  2. World Health Organization. Ambient (outdoor) air pollution in cities database 2014 [Internet]. 2014. Geneva: World Health Organization; 2014 [cited 2015 Dec 29]. Available from: http://www.who.int/phe/health_topics/outdoorair/databases/cities/en/
  3. Wheeler AJ, Smith-Doiron M, Xu X, Gilbert NL, Brook JR. Intra-urban variability of air pollution in Windsor, Ontario—measurement and modeling for human exposure assessment. Environ Res. 2008;106(1):7-16.
  4. Jerrett M, Arain MA, Kanaroglou PF, Beckerman BF, Crouse D, Gilbert NL, et al. Modeling the intraurban variability of ambient traffic pollution in Toronto, Canada. J Toxicol Environ Health A. 2007;70(3-4):200-12.
  5. Ontario. Ministry of the Environment and Climate Change. Air quality in Ontario 2013 report [Internet]. Toronto, ON: Queen's Printer for Ontario; 2015 [cited 2015 Dec 29]. Available from: http://www.airqualityontario.com/downloads/AirQualityInOntarioReportAndAppendix2013.pdf
  6. Ontario Agency for Health Protection and Promotion (Public Health Ontario), Kim JH, Copes R. Case Study: Health effects of traffic related air pollution in a small community [Internet]; 2015 [cited 2015 Dec 29]. Available from: https://www.publichealthontario.ca/en/eRepository/Traffic_Pollution_Small_Community_2015.pdf
  7. Health Effects Institute. Traffic-related air pollution: a critical review of the literature on emissions, exposure, and health effects. Special report 17 [Internet]. Boston, MA: Health Effects Institute; 2010 [cited 2015 Dec 29]. Available from: http://pubs.healtheffects.org/getfile.php?u=553
  8. Loomis D, Grosse Y, Lauby-Secretan B, El Ghissassi F, Bouvard V, Benbrahim-Tallaa L, et al. The carcinogenicity of outdoor air pollution. Lancet Oncol. 2013;14(13):1262-3.
  9. Government of Ontario. Government of Ontario IT standard (GO-ITS #29). Ontario Road Network (ORN) data standard for road geometry and attributes [Internet]. Toronto, ON: Queen's Printer for Ontario; 2009 [cited 2015 Dec 29]. Available from: https://dr6j45jk9xcmk.cloudfront.net/documents/1866/go-its-29-ontario-road-network-orn.pdf
  10. Karner AA, Eisinger DS, Niemeier DA. Near-roadway air quality: synthesizing the findings from real-world data. Environ Sci Technol. 2010;44(14):5334-44.
  11. Statistics Canada. Summary tables: Population estimates and projections –Population, urban and rural, by province and territory (Ontario) [Internet]. Ottawa, ON: Her Majesty the Queen in Right of Canada; 2011 [cited 2015 Dec 29]. Available from: http://www.statcan.gc.ca/tables-tableaux/sum-som/l01/cst01/demo62g-eng.htm
  12. Toronto Public Health. Air pollution burden of illness from traffic in Toronto: problems and solutions [Internet]. Toronto, ON: City of Toronto; 2007 [cited 2015 Dec 29]. Available from: http://www.toronto.ca/legdocs/mmis/2007/hl/bgrd/backgroundfile-8046.pdf
  13. Evans GJ, Jeong CH, Sabaliauskas K, Jadidian P, Aldersley S, Larocque H, Herod D. Design of a near-road monitoring strategy for Canada. SOCAAR report no. CR -WB-2011-01-01. Toronto, ON: Southern Ontario Centre for Atmospheric Aerosol Research, University of Toronto; 2010.
  14. Ries, FJ, Hystad P, Gouge B. Minimizing children's non-residential exposure to traffic-related pollution. Vancouver, BC: National Collaborating Centre for Environmental Health; 2010. Available from: http://www.ncceh.ca/sites/default/files/Children_Exposure_Traffic_Pollution_Aug_2010.pdf
  15. Makri A, Stilianakis NI. Vulnerability to air pollution health effects. Int J Hyg Environ Health. 2008;211(3-4):326-36.
  16. Simoni M, Baldacci S, Maio S, Cerrai S, Sarnno G, Viegi G. Adverse effects of outdoor pollution in the elderly. J Thor Dis. 2015;7(1):35-45. Available from: http://www.jthoracdis.com/article/view/3771/4219
  17. Boehmer TG, Foster SL, Henry JR, Woghiren-Akinnifesi EL, Yip FY. Residential Proximity to Major Highways — United States, 2010. MMWR Surveill Summ. 2013;62(Suppl 3):46-50. Available from:http://www.cdc.gov/mmwr/pdf/other/su6203.pdf
  18. Weichenthal S, Van Ryswyk K, Kulka R, Sun L, Wallace L, Joseph L. In-vehicle exposures to particulate air pollution in Canadian metropolitan areas: the urban transportation exposure study. Environ Sci Technol. 2015;49(1):597-605
  19. Int Panis L, de Geus B, Vandenbulcke G, Willems H, Degraeuwe B, Bleux N, et al. Exposure to particulate matter in traffic: a comparison of cyclists and car passengers. Atmos Environ. 2010;44(19):2263-70.
  20. Hoek G, Krishnan RM, Beelen R, Peters A, Ostro B, Brunekreef B, et al. Long-term air pollution exposure and cardio- respiratory mortality: a review. Environ Health. 2013;12(1):43. Available from: http://www.ehjournal.net/content/pdf/1476-069X-12-43.pdf
  21. Pope CA 3rd, Dockery DW. Health effects of fine particulate air pollution: lines that connect. J Air Waste Manage Assoc. 2006;56(6):709-42.
  22. International Agency for Research on Cancer. Diesel and gasoline engine exhausts and some nitroarenenes. IARC Monographs Volume 105. Lyon, France: International Agency for Research on Cancer; 2014. Available from: http://monographs.iarc.fr/ENG/Monographs/vol105/mono105.pdf

Report last updated: March 15, 2016

Page last reviewed:  
Page last updated: 07/04/2016 1:52 PM
Uncontrolled print copy. Valid only on day of Print: [date]
Page updated on [date/time] 07/04/2016 1:52 PM
© , Ontario Agency for Health Protection and Promotion