Skeena Region EPD

Conditions & Interpretation

Air Quality Conditions

Current air quality conditions for stations throughout British Columbia are available by clicking here.

Skeena Region stations include:

Burns Lake
Houston
Kitimat
Port Edward
Prince Rupert
Smithers
Telkwa
Terrace

Air Quality Interpretation

What is the Air Quality Index?
An Air Quality Index (AQI) is a way of transforming complex air quality measurements into a single number or descriptive term. It describes both the measured air quality and the publicly perceived air quality at any given time. The British Columbia AQIs are directly comparable to AQIs issued in all major Canadian cities, since BC follows the same federal guidelines.

How is an AQI interpreted?
The AQI numbers are interpreted thus:

Why issue an Air Quality Index?
The main purpose is to inform the public about the present state of air quality. Having a daily Air Quality Index available via the media builds an awareness in the public: people will for the first time be able to draw comparisons between the measured air quality and what they directly sense.

For asthmatics and other concerned residents, it may even influence their behaviour. For example, in a situation where the AQI is high (above 50), people with respiratory problems may choose to refrain from strenuous exercise or temporarily avoid the polluted region.

How is an AQI calculated?
Common air pollutants are measured continuously at state-of-the-art monitoring stations throughout British Columbia. This information is gathered by a central computer in Victoria and an hourly AQI value is then calculated.

The AQI is not an amalgamation of all measured pollutants, but the value of the pollutant with the highest AQI number. Every hour, each pollutant's concentration is converted into an AQI number according to a methodology developed by Environment Canada and the provincial environment ministries. The highest AQI number becomes that hour's overall AQI value. When issuing the AQI it is common practice to note which pollutant is "driving" the AQI.

The AQI for a given concentration of each pollutant is determined from a set of straight line interpolations that start at zero and go through break-points at AQI values of 25, 50 and 100. These break-points represent the limits of good, fair and poor air quality. The ambient (outdoor surrounding air) values of the break-points for the different pollutants measured over a set of averaging periods are as follows:

What is the concern about particulate matter?
Particulate matter (PM₁₀) is matter containing airborne particles with a diameter less than 10 microns (micrometres). Such particles are able to penetrate deep into to the respiratory tract and make breathing more difficult. The latest research indicates that for each increment of 10 that the AQI exceeds 20 there are the following health outcomes related to inhalable particulates (PM₁₀):

• a 0.8% increase in hospitalizations and a 1% increase in emergency room visits for respiratory illnesses;
• a 9.5% increase in days of restricted activity due to respiratory symptoms;
• a 4.1% increase in school absenteeism, and a 1.2% increase in reporting of cough.

(Source: Health Effects of Inhalable Particles: Implications for British Columbia).

The people who are most sensitive to the impacts of PM₁₀ include children, the elderly, and those with pre-existing lung and heart disease.

For more information about fine particulates, see Particulate Matter. Also, the Environmental Quality Branch site has several publications on fine particulates and smoke, including: Fine Particulates: What They Are and How They Affect Us.

What is the Odour Index?
The Odour Index is calculated separately from the Air Quality Index, and is used to indicate the presence of pollutants that, aside from their odour, do not at low concentrations pose a concern to health or the environment. Pollutants that create an odour problem are generally comprised of compounds that contain sulphur in its reduced chemical state.

An Odour Index of 26 or greater indicates that reduced sulphur compounds are present in a total concentration greater than the "Desirable" Provincial Ambient Level. An Index of 51 or greater indicates concentrations in excess of the "Interim" Provincial Ambient Level.

The Odour Index for a given Reduced Sulphur concentration is determined from a set of linear interpolations starting at zero and having break-points at values of 25, 50 and 100. The ambient values of the break-point concentrations measured over 1-hour and 24-hour averaging periods are as follows:

updated: may 2006