Squamish Air Quality

Frequently Asked Questions

What are the different types of pollutants?

Air quality is typically determined by measuring four different types of air pollutants, fine particulate matter, nitrogen dioxide, ozone and sulphur dioxide.

PM_2.5 fine particulate matter is particles that are 2.5 microns (0.0025mm) or less in diameter. These fine particles can enter the eyes, nose, throat and lungs, causing irritation and other health effects. PM_2.5 fine particulate matter typically comes from vehicles, industrial processes and burning fuels. PM_2.5 concentrations will be very high when wildfire smoke is present.

Nitrogen dioxide (NO₂) is typically formed when gas, diesel or other fossil fuels are burned at high temperatures. Nitrogen dioxide can cause airway inflammation and can increase the likelihood of asthma attacks.

Ozone (O₃) is a principal component of smog, and is formed when nitrogen oxides and volatile organic compounds (VOCs) are exposed to sunlight. VOCs are generated both by human activities, such as gas combustion, and from natural sources, such as coniferous forests. Ozone frequently causes irritation of the eyes, nose and throat.

Sulphur dioxide (SO₂) typically originates from industrial processes that burn sulphur-containing materials, such as coal-fired power plants. Sulphur dioxide can cause airway inflammation and can increase the likelihood of asthma attacks.

What do the bars under the pollutant values mean?

The bars indicate how the current hourly pollutant values compare to the provincial and Canadian air quality objectives. For example, if the bar goes halfway across, the current pollution level is half that of the air quality objective. If the current pollutant value is higher than the air quality objective, the bar will fill the entire area and appear striped.

The air quality objectives in use are 60ppb for NO₂, 82ppb for O₃, and 70ppb for SO₂. A provincial or national air quality objective has not been set for the hourly value of PM_2.5, only for the 24 hour average value, which is 25µg/m³. The site uses a value of twice this, 50µg/m³, as an hourly air quality objective for PM_2.5 pollutants, but this is not a recognised standard objective.

What is the difference between the AQHI index and the AQHI-Plus index?

The AQHI, or Air Quality Health Index, is the standard index used to indicate air quality across Canada. It is calculated from measurements of fine particulate matter, nitrogen dioxide, ozone and sulphur dioxide, and provides a single figure for air quality that is easy to understand and compare. The AQHI index was first introduced in BC in 2005.

The AQHI-Plus index is a modification of the AQHI that is more responsive to wildfire smoke. Because the original AQHI index is influenced by four types of pollutants, wildfire smoke, which creates very high fine particulate matter pollutants but doesn't create any of the other pollutants, can result in an AQHI index that is artificially low.

When fine particulate matter pollutants are not significantly higher than other types of pollutants, the AQHI and AQHI-Plus indices will show the same value, but when there is a high concentration of fine particulate matter pollutants compared to other pollutants, the AQHI-Plus index will give a higher, more accurate indication of the overall air quality.

The AQHI-Plus index was piloted in BC in 2018, and was adopted as the standard air quality index across BC in 2021.

What is the AQI index?

The AQI index is the air quality index used across the United States. For the benefit of US visitors who may be more familiar with the AQI index than the Canadian AQHI and AQHI-Plus indices, the site calculates the AQI index from the individual pollutant concentrations.

Where is this data sourced from?

The raw pollutant data is sourced from the BC Ministry of Environment monitoring station located at the Squamish Elementary school. This data is typically updated once per hour. The pollutant data is converted into an air quality index value using the appropriate formulae.