About the indicator

Nitrogen dioxide, or NO2, is an air pollutant that can negatively affect human health and the environment. Exposure to NO2 can lead to increased risk of respiratory problems. NO2 also adversely affects ecosystems when it is deposited onto the surface, for example through rain.

The major sources of NO2 are the burning of fuels for vehicles, home heating and industrial processes. NO2 also occurs naturally in the environment due to forest fires, lightning or emissions from the soil.

NO2 contributes to the development of other air pollutants, such as ozone, nitric acid and particulate matter. Near large cities, it is partly responsible for the brownish colour of the air in the lower atmosphere.

NO2 is part of the Air Quality Health Index (AQHI) that reports on health risks associated with local air quality across Alberta in real-time.

This indicator reports on the concentration of NO2 from 2000 to 2020 and compares it to Alberta’s Ambient Air Quality Objectives (AAQO). The Alberta objectives set thresholds for air pollutants to protect human and ecosystem health. This indicator also discusses future management of NO2 levels in Alberta under the Canadian Ambient Air Quality Standards (CAAQS).

How condition of environment indicators for air are used

This condition of environment indicator reports on the current state and trends in Alberta’s air across the province. The air indicators were selected, prepared and reported on to meet this purpose.

Other types of reporting, such as CAAQS reporting (through Alberta’s Air Zone Reports) or compliance reporting near an industrial facility have different purposes and requirements. Therefore, other reporting may use different data sets, data analysis methods, or time-periods and are not directly comparable to the condition of environment reporting. For further details, visit:


Levels of NO2 are higher in urban areas, with Alberta’s highest levels in Edmonton and Calgary.

Levels of NO2 have been decreasing throughout much of the province over the past 2 decades due to improved technology at emissions sources, including personal vehicles and industry.

Despite the decreasing trend, NO2 levels in urban areas will approach or even exceed the new Canadian Ambient Air Quality Standards, which are national standards to protect human health and the environment.

  • Variation across Alberta

    • Figure 1 (PNG, 660 KB) shows that Alberta’s cities see higher concentrations of NO2 when compared to smaller communities, with Edmonton and Calgary showing the highest concentrations of NO2 in the province.
    • Increased NO2 levels in cities occur due to a higher number of emission sources including vehicles. Industrial sources that emit NO2 are also often located in or near urban areas.
    • NO2 levels are also somewhat elevated near major industrial sources, such as in the mineable oil sands region and the industrial heartland to the east of Edmonton.
  • Changes over time

    • Figure 2 (PNG, 22 KB) shows that between 2000 and 2020, Alberta saw an overall decrease of annual average concentrations of NO2 when averaged across all monitoring stations. This trend is consistent with trends across Canada as improved technologies lowered NO2 concentrations from various emissions sources.
    • Most major population centres, including Edmonton and Calgary, saw a decrease in NO2 levels. Levels remained steady for Grande Prairie and Fort McMurray, potentially due to increased industrial operations and population growth that may offset improved emission technologies in these regions.
    • More recently, between 2011 and 2020 NO2 levels increased at some monitoring stations. Levels at these stations are low compared to stations located in larger cities or near major industrial sources.
  • Comparison to provincial objectives

    • Alberta’s Ambient Air Quality Objectives (AAQOs) provide maximum acceptable thresholds for over 30 airborne compounds to protect human and ecosystem health. All industrial facilities must be designed and operated to ensure ambient air quality remains below these thresholds. When air quality exceeds an AAQO, the Alberta government assesses the cause and determines whether corrective action is required.
    • Since 2005, NO2 levels have consistently been below the annual Alberta objective for all stations across the province. The annual objective for NO2 is 24 parts per billion (ppb) based on the protection of ecosystems.
    • In 2020, there were no exceedances of the one-hour Alberta objective. Historically, exceedances of the one-hour objective have occurred infrequently – 0 to 3 times per year – in various locations across Alberta. The one-hour objective is 159 ppb based on the protection of human health.
  • Comparison to national standards

    • NO2 is a new indicator for the Canadian standards and will be reported on for the first time using data from 2018 to 2020.
    • Current NO2 levels in Alberta will approach or even exceed the Canadian standards in urban areas, despite the decreasing trend in NO2 concentrations seen across Alberta, as the Canadian standards have lower thresholds than the current Alberta objectives for NO2.
    • Ongoing work will be needed to manage NO2 levels in some areas of the province so that national thresholds are not exceeded. This may include knowledge improvement, policy changes, regulatory action, engagement to promote behavioural changes, and implementation of technology to reduce emissions.
    • Management levels for the Canadian standards for NO2 will be assigned when the assessment of 2018 to 2020 data is complete. Information presented here is not an assessment of the achievement status of the Canadian standards.
    • Annual reporting of Alberta’s air quality against Canadian Ambient Air Quality Standards is available in Alberta’s Air Zone Reports.
Figure 1 - Annual average NO2 concentrations across Alberta for 2020

Figure 1. Annual average NO2 concentrations across Alberta for 2020

View large image: Figure 1 (PNG, 660 KB)

Figure 1 - Annual average NO2 concentrations across Alberta for 2020

Figure 2. Trends in annual average NO2 concentrations over time. Trends are indicated in the legend (○ = no significant trend detected; ∆ = increasing trend; ∇ = decreasing trend)

View large image: Figure 2 (PNG, 22 KB)

Focused study

On March 16 2020, Alberta declared a public health emergency and enacted measures to reduce the spread of COVID-19. Measures included the closure of schools and daycares, the restriction of gatherings, and mandated physical distancing. These actions were expected to temporarily decrease the concentration of air pollutants due to reduced road traffic in Alberta’s urban centres.

The change in NO2 concentrations during the spring 2020 COVID-19 public health emergency at selected urban centres is shown in Figure 3. Mean concentrations of NO2 during the spring 2020 public health emergency and the same time-period in previous years (2015-2019) are shown, with percent differences indicated in Figure 3 (PNG, 636 KB).

  • Between March 16 and April 24, 2020, concentrations of NO2 in the air in Alberta’s 2 largest cities, Calgary and Edmonton, were at least 14% lower than in previous years.
  • Decreases in NO2 levels were also observed in satellite data for urban areas in Alberta.
  • Decreased NO2 concentrations coincided with 8 to 41% decreases in road traffic, which is a major emission source in cities.

For further details, visit:


Figure 3 - Mean NO2 concentrations in a number of urban centres.

Figure 3. Mean NO2 concentrations in a number of urban centres. Data include sample period between March 16 to April 24 (excluding weekends and holidays). Significance was tested using Mann Whitney u test (p value ≤ 0.05). This test compares the distribution of the 2 data sets.

View large image: Figure 3 (PNG, 636 KB)

Alberta Air Data Warehouse
Access long-term air quality monitoring data for Alberta.

Air Monitoring
Information on air monitoring in Alberta.

Alberta Air Zone Reports
Annual reporting of Alberta’s air quality against Canadian Ambient Air Quality Standards.

Ambient Air Quality Objectives (AAAQOs)
Review the provincial standards used to evaluate air quality in Alberta.

Canadian Ambient Air Quality Standards 
Alberta’s ambient air monitoring data and management levels are assessed annually against national standards.

Condition of the Environment Report – Air Component (PDF, 397 KB)
Information on data analysis methods and tools.

Environment and land use planning
Learn more about how air quality in Alberta is managed through regional land use planning.

Contact Alberta's Environmental Science Program or the Office of the Chief Scientist:

Email: [email protected]

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