12.1 Criteria Air Contaminants Indicator

Last Updated: 
September 25, 2015
Monitoring Criteria Air Contaminants (CACs) is an indicator of air quality.

Air quality monitoring instruments.
Air quality monitoring instruments.

CACs are the common trace particles and gases found in ambient air that monitoring programs target most often. CACs include total suspended particulate (TSP), particulate matter 10 microns or less in diameter (PM10), particulate matter 2.5 microns or less in diameter (PM2.5), and gaseous pollutants including sulphur dioxide (SO2), nitrogen oxide (NOX), carbon monoxide (CO) and ground level ozone (O3).

National and territorial standards establish limits for the maximum amount of particulates and gases that can be in ambient air. Actual measured concentrations are compared to these standards to determine the quality of air.

A variety of methods exist to measure individual CACs. These methods range in complexity and sophistication from relatively simple filter-based grab sampling and subsequent laboratory analysis to electronic particulate and gas analyzers providing continuous up-to-the-minute analysis.

Information for this indicator is obtained from the NWT Air Quality Monitoring Network1, a program operated by ENR in collaboration with Environment Canada3.

The Network consists of four monitoring stations:

  • Yellowknife – Taiga Shield
  • Inuvik – northern edge of Taiga Plains
  • Fort Smith – southern Taiga Plains
  • Norman Wells – central Taiga Plains

Pollutants monitored vary by station but include most, if not all, of the CACs. Wind speed, wind direction and temperature are also monitored.

NWT Focus

The NWT has limited industrial development, a small population and many remote and small communities.The only relatively large community is Yellowknife.

Industrial development, in particular resource extraction such as mining and upstream oil and gas, is likely to increase in the future. This will be associated with an increase in emissions of air pollutants. Increased development activity may also result in community growth, which can produce additional emissions from sources such as diesel power generation, construction, increased vehicle use and commercial and residential heating. It is important to establish baseline conditions by measuring selected CACs in communities before development activities take place. This provides a basis for comparison and management of air quality and emissions. Ongoing monitoring allows for the tracking of trends and cumulative impacts as development proceeds.

Current view: status and trend

Information from all air monitoring activities, along with some historical perspective and trend analysis, is presented annually in the NWT Air Quality Report2. Concentrations of CACs in the NWT are expected to be low with readings at or close to what would be considered typical background values.

Monitoring to date generally confirms the expected very low readings for most air contaminants measured in the four selected NWT communities, with concentrations well below established air quality standards.

Notable exceptions include the influence of wildland fire smoke on particulate concentrations (PM2.5, PM10) as well as spring and summer dust events from residual gravel on the roads following thaw or unpaved roads, which produce short term elevated PM10 concentrations. 2014 was an exceptionally active wildfire season with many of the fires occuring in the Taiga Shield and in the southern section of the Taiga Plains (the North and South Slave regions). Very high ambient particulate measurements (PM2.5, PM10) were recorded in Yellowknife as a result of the smoke from wildland fires. The chart below shows that PM2.5 levels tend to fluctuate slightly over the years. Again, 2014 is significantly higher due to the active fire behaviour and conditions.

Average annual emission and number of hourly exceedances of PM2.5 in Yellowknife, 2004-current. Source: NWT Air Quality Reports.

Historically, the influence of emissions from industrial operations on community air quality has been observed. Up until the end of the 1990s gold mine ore roasters, the most recent  operated by Giant Mine, resulted in high sulphur dioxide readings in Yellowknife. As can be seen from the chart, hourly readings exceed established air quality standards on a number of occassions but dropped to zero after 1999 when the last Yellowknife mine closed. Only background levels have been recorded since then. This emphasizes the importance of appropriately managing emissions from local significant sources, such as industrial operations.

Average annual emission and number of hourly exceedances of sulphur dioxide in Yellowknife, 1994-current. Source: NWT Air Quality Reports.

Looking forward

Industrial development is expected to increase in the NWT with the continued exploitation of mineral and oil and gas resources. It is reasonable to assume air emissions associated with these activities will also increase. Currently, the vast majority of industrial activity is occurring in remote areas and the potential risk to community air quality and residents is low. However, the potential for localized environmental impacts is present and, if the activity becomes sufficiently intense and widespread, the cumulative emissions could begin to affect regional air quality including the air in communities.

Increased industrial activity may alsoy trigger increased community growth in the form of commercial and residential developments. Emissions associated with these activities (increased space heating, power demands, vehicles, etc) would have a more direct impact on community air quality. The challenge will be to effectively manage industrial and community growth to ensure  economic benefits for the residents of the NWT are realized while ensuring emissions from this development activity do not result in unacceptable impacts to air quality. Since combustion sources are a large source of CAC emissions, efforts to improve energy efficiency and/or the use of alternative energy sources to reduce greenhouse gas production can also have the co-benefit of reducing CAC emissions.

Wildland fires are the main natural sources of air pollutants in NWT communities. Climate change models predict an increase in the severity of fire seasons in Canada's boreal forests (see Big Picture Focal Point) including longer fire seasons (see Vegetation Focal Point). A decline in air quality in some NWT communities may become more common, especially during the summer months.

Looking around

The measurement and use of CACs to determine air quality is a well-established approach across North America, Europe and many other countries. Two NWT monitoring stations (Inuvik and Yellowknife) are designated as part of the National Air Pollution Surveillance (NAPS) program1, which monitors and compares air quality in communities across Canada. The informatio is  summarized  in annual reports. Data from the NWT monitoring network is also used by other jurisdictions for comparative purposes in their air quality report; by air quality specialists in the NWT to manage and track air quality issues; by consultants providing assessments in support of development projects in the NWT; and, by residents of the NWT and across Canada through the NWT Air Quality Monitoring Network web site1.

PM2.5 average concentrations from each of the NWT monitoring stations from 2005-2013 (year 2014 not shown). Source: NWT air quality reports 2013.

In  2014, the PM2.4 levels for Yellowknife surpassed the US EPA National Ambient Air Qualtiy Standard for PM2.5. Annual mean of 12 ug/m3. Over the past decade, the Yellowknife station had demonstrated a slight upward trend in PM2.5 levels. These higher levels could be attributed to a variety of factors, including localized sources or natural causes (e.g. wildland fires). The higher levels in 2014 were clearly from smoke released by wildland fires.

Air quality monitoring data from our Yellowknife station is used in the Canadian Environmental Sustainability Indicators (CESI) reports. NWT air quality data is supplied by ENR to the National Air Pollution Surveillance (NAPS) Program, which makes it available to the CESI authors.



Find More

  • The NWT Air Quality Monitoring Network links to a data management, analysis and reporting system to provide public access to ‘almost real-time’ air quality data for each monitoring location. Access to archived data is available by querying the database using web-based tools. The web site also provides additional information on the NWT Air Quality Monitoring Network, air pollutants, monitoring equipment and air quality standards, as well as links to monitoring information collected in other jurisdictions.
  • Monitoring data from all NWT stations is analyzed and presented in the annual NWT Air Quality Reports 

Other focal points

  • Go to Big Picture for information on climate change model predictions on forest wildfires.
  • Go to Vegetation for information on annual number of forest wildfires and total area burned.
  • Go to Energy Use for information on fossil fuel use and sources of greenhouse gas emissions, which produce CACs.

Technical Notes

More detailed information on monitoring methodology is available on the NWT Air Quality Monitoring Network website. Each station is a climate-controlled trailer with state-of-the-art monitoring equipment capable of continuously sampling and analyzing a variety of air pollutants and meteorological conditions. Using sophisticated data acquisition system and communications software, data from each station is automatically transmitted every hour to ENR headquarters in Yellowknife, allowing almost real time review of community air quality by ENR staff. The data also undergoes a series of 'on the fly' validity checks before being archived by ENR’s data management, analysis and reporting system.


Found an error or have a question? Contact the team at NWTSOER@gov.nt.ca.


Ref. 1 - GNWT ENR Environmental Protection. 2011. NWT Air Quality Monitoring Network.

Ref. 2 - GNWT ENR Environmental Protection. Current. NWT Air Quality Reports.

Ref. 3 - Environment Canada. 2008. National Air Pollution Surveillance (NAPS) program.