Guide to Air Quality Health Index forecasts: chapter 1

Air Quality Health Index forecast bulletins

The Air Quality Health Index (AQHI) forecast bulletin provides both a quantitative and qualitative description of the air quality health index expected within the next two days (refer to Table 1 for exact time periods).

The AQHI is a personal health protection tool providing individuals with air quality conditions and concrete measures that they can take to reduce the risk associated with air pollution. The AQHI is calculated based on the relative risks of a combination of common air pollutants which are known to harm human health. These pollutants include Ozone (O3) at ground level, Particulate Matter (PM2.5/PM10) and Nitrogen Dioxide (NO2).

When are forecasts issued?

The AQHI forecast bulletins are issued two times per day: the first one is issued between 5:00 a.m. and 6:00 a.m., and the second one is issued between 4:00 p.m. and 5:00 p.m. local time.

What time period does the forecast cover?

The following table indicates the time period that the forecast covers for each of the two forecast issue times. The issue times of the bulletin are within a half-hour of the times indicated above.

Table 1 : Time periods for the AQHI forecast bulletins

Forecast Issued at: Today Tonight Tomorrow
5:00 a.m. - 6:00 a.m. 6:00 a.m. to 6:00 p.m. 6:00 p.m. to 6:00 a.m. 6:00 a.m. to Midnight (12:00 a.m.)
4:00 p.m. - 5:00 p.m. N/A Issue time to 6:00 a.m. 6:00 a.m. to Midnight (12:00 a.m.)

Below, the same information can be seen along a timeline:

5:00 a.m. - 6:00 a.m. forecast issue

5:00 a.m. - 6:00 a.m. forecast issue. Refer to Table 1 for description.

4:00 p.m. - 5:00 p.m. forecast issue:

4:00 p.m. - 5:00 p.m. forecast issue. Refer to Table 1 for description.

How are forecast regions defined?

Forecast regions are closely aligned with cities, communities and municipal boundaries. Local factors such as terrain, land cover and population patterns were used to define these regions. The names of the forecast regions generally correspond with those of the most prominent communities or geographic regions. The names were chosen on the basis of how well they represent the area covered by the region. All official place names can be found in the Canadian Geographical Names Database.

What information is included in the forecast?

Days 1 and 2:

The AQHIforecast bulletin will always contain the following standard elements (see Air Quality Elements for further details):

  • Maximum Air Quality Health Index (AQHI)
  • Health Risk Category
  • AQHI Scale

Sample forecasts

Sample forecast (


SAMPLE forecast ( Details can be found below.
  1. The Navigational toolbar that allows you to quickly link to other meteorological products and educational resources offered by Environment Canada; from radar and satellite images, marine information to fact sheets and Frequently Asked Questions.
  2. The Air Quality Health Index scale shows you the AQHI range and corresponding risk category.
  3. The Current Conditions displays AQHI information for the location chosen, along with the time and date that the information is valid.
  4. The 24 hour history provides the AQHI and risk category for the past 24 hours.
  5. The At-Risk and General Populations text provides information to the current AQHI value for each group.
  6. The Health Message Tab provides you with the health information for each risk category for both the At-Risk and General populations.
  7. The Forecast Maximums provides the complete AQHI forecast. See SAMPLE regular forecast for a more detailed explanation of our text forecasts.
  8. The Next 18 hr provides an hourly forecast of the AQHI for the next 18hr
  9. The Who is at risk? text provides information about risk groups and where to go for further information.
  10. The Did you know…? text provides facts related to air quality.
  11. The Initiative information provides the names of Environment Canada, Health Canada and the provincial partners.

Sample regular forecast (text bulletin)

The numbers provide a description of the forecast text.
  1. FLCN21 CWHX 042000
    Air Quality Health Index forecast for Nova Scotia issued jointly by Environment Canada and Nova Scotia Environment and Nova Scotia Health Promotion and Protection at 5.00 pm ADT Monday 4 May 2009 for tonight and Tuesday. The next scheduled forecast will be issued at 6.00 am Tuesday.
  2. Halifax
  3. Tonight...Maximum Air Quality Health Index 2 or low risk.
    Tuesday...Maximum Air Quality Health Index 1 or low risk.
  4. Air Quality Health Index Scale:
    1-3  Low health risk
    4-6  Moderate health risk
    7-10 High health risk
    Above 10 Very high health risk
  5. For more information, consult Air Quality Health Index website
  1. This text is called the “title block”. It indicates the forecast area, the date and the time for which the forecast is. It also indicates when the next forecast will be issued.
  2. The forecast region name(s) is the full name of the region(s) or metropolitan area(s) for which the forecast is issued.
  3. The forecast text is broken into distinct periods (i.e. today, tonight, tomorrow) for ease of readability. See Table 1 for information on the times associated with the different periods.
  4. The Air Quality Health Index scale shows the AQHI range and corresponding risk category.
  5. Link to more information.

Forecast revision

The Air Quality Health Index forecast is amended when forthcoming conditions are expected to be significantly different from those originally forecasted, but only in a way that public safety is at risk, or when public inconvenience will be extensive. Making an amendment is always at the forecaster’s discretion. An amendment to the Air Quality Health Index forecast bulletin is initiated when the following criteria have been satisfied:

  • If the AQHI value rises or falls two or more index values on the AQHI scale; and
  • If it is expected to stay at that value for four hours or more.
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