About the Air Quality Health Index (AQHI)

What is the AQHI

The Air Quality Health Index (AQHI) scale

The AQHI is a scale ranging from 1-10+. It shows you the risk that air quality in your area may have on your health.

Figure 1. Air Quality Health Index scale

Long description

Coloured bar that represents the progressive range of four categories of air quality risk levels from low risk to high risk. Colours start with light blue, medium blue, dark blue, with the numbers 1, 2, and 3 below the colours to show levels 1, 2, or 3 for Low Risk (1 to 3). Next is light yellow, dark yellow and orange with the numbers 4, 5, 6 below the colours to show levels 4, 5 or 6 for Moderate Risk (4 to 6). Following is pink, light red, and dark red with the numbers 7, 8, 9, 10 below the colours to show levels 7, 8, 9, 10 for High Risk (7 to 10). Finally, a block of dark burgundy/brown with a plus sign below it to show level 10+ for Very High Risk.

You’ll see four risk categories on the AQHI scale. They range from low to very high risk. The colours go from blue to red to show increasing risk, and the scores range from 1 to 10+.

Each risk category has health recommendations for the general population and people at risk, who are more vulnerable to poor air quality.

People at risk include:

children
people over 65 years
those with health conditions

Risk categories and health recommendations

Use these categories to quickly identify the risk to your health.

Low risk (AQHI 1 to 3)

everyone
- enjoy your usual outdoor activities

Moderate risk (AQHI 4 to 6)

general population
- continue usual outdoor activities unless you have symptoms like coughing and throat irritation
people at risk
- consider reducing or rescheduling strenuous outdoor activities if you have symptoms like coughing or throat irritation

High risk (AQHI 7 to 10)

general population
- consider reducing or rescheduling strenuous outdoor activities if you have symptoms like coughing and throat irritation
people at risk
- reduce or reschedule strenuous outdoor activities

Very high risk (AQHI 10+)

general population
- reduce or reschedule strenuous outdoor activities, especially if you have symptoms like coughing and throat irritation
people at risk
- avoid strenuous activities outdoors

How we calculate the Air Quality Health Index (AQHI)

We calculate the AQHI based on the relative risks of a combination of common air pollutants that are harmful to human health. These pollutants are:

ozone (O₃) at ground level
particulate matter (PM_2.5/PM₁₀)
nitrogen dioxide (NO₂)

Ground-level ozone (O3)

Ground-level ozone is formed by photo-chemical reactions in the atmosphere. It can be a major part of smog during the summer, especially during hot sunny weather. Ground-level ozone is generally low in the wintertime.

Ozone can travel long distances in a polluted air mass, and it can be responsible for large regional air pollution episodes.

Fine particulate matter (PM2.5)

Fine particulate matter is a mixture of tiny airborne particles that can be inhaled deep into your lungs. Fine particulate matter comes from vehicles, industrial facilities, or natural sources like forest fires. It can also come from chemical reactions among other pollutants. Particulate matter can be part of both local air pollution sources and widespread air pollution episodes.

Nitrogen dioxide (NO2)

Motor vehicle exhaust and power plants that use fossil fuels release nitrogen dioxide. Nitrogen dioxide is part of how ground level ozone and fine particulate matter are formed. Nitrogen dioxide is often at high levels in the near high traffic roadways and other local sources.

How we calculate AQHI for wildfire smoke events

Wildfire smoke causes quick rises in fine particulate matter (PM_2.5) in the air. During a wildfire smoke event, we adjust the AQHI formula, so that we only use PM_2.5 to calculate the AQHI on an hourly basis.

We do this to respond to the changes in PM_2.5concentrations. As a result, we can determine health risks more accurately during high and very high smoke events.

How we calculate AQHI in your community

Air monitoring stations across Canada measure the AQHI.

For most communities, the AQHI value is an average from local stations, carefully chosen to represent the community.

Air pollution changes over time and distance, so readings can vary within a community. Areas near traffic or industry usually have higher pollution.

The AQHI uses an average because people move around their communities and may be exposed to air pollutants from different places during daily activities. An average gives the best estimate of the air mixture you breathe. Therefore, your community AQHI may be different from readings at individual stations.

When we started using the AQHI instead of the Air Quality Index

Canada began using the AQHI on June 24, 2007. The AQHI replaced the Air Quality Index (AQI). The AQI is based on individual pollutant levels instead of health impacts like the AQHI. All of Canada uses the AQHI, except for Québec which uses the Info-Smog program.

Air quality alerts

We issue air quality alerts when we expect air pollution to rise, or when it is already high.

High air pollution can happen because of:

wildfire smoke
urban pollutants
industrial activity

All of these events can increase harmful substances in the air like fine particles (PM_2.5), ground-level ozone, or nitrogen dioxide.

Air quality alerts give you information to help you protect your health. They explain what’s happening, what the impact might be, and what actions you should take.

Air quality alerts are colour-coded (yellow, orange, or red) based on possible risks. The AQHI helps us determine when to issue an alert, and what colour to use. Learn more about colour-coded alerts.

Your AQHI forecast

Find your local Air Quality Health Index (AQHI)

Select your location on the Local Air Quality Health Index page or on the WeatherCAN app.

You can set up custom air quality notifications with WeatherCAN.

If you live outside the AQHI community areas, you can get resources about air quality through your local:

public health office
Ministry of Environment
lung and asthma association chapters

Understand your Air Quality Health Index (AQHI) forecast

Your AQHI forecast has the following elements:

observed conditions
health recommendations
forecast maximums

The observed conditions section shows you the most recently calculated AQHI value. In the sample image below, the observed AQHI is Level 3, low risk.

Under the scale, you will see health recommendations for at risk populations and for the general population.

Figure 1. Observed conditions and health recommendations

Long description

Air Quality Health Index for Metro Vancouver – NW showing a value of 3, which falls in the low-risk range. A colour scale from 1 to 10+ indicates increasing health risk. Guidance below states that both the general population and at‑risk groups can enjoy usual outdoor activities.

The forecast maximums section shows you the forecasted AQHI levels for the next two days and nights (72 hours).

Figure 2. Forecast maximums

Long description

Air Quality Health Index forecast showing low‑risk values of 2 for Tuesday, Tuesday night, Wednesday, and Wednesday night. Each line includes a colour bar ranging from blue to dark red, with a marker positioned over the number 3 in the low‑risk zone.

Plan with the AQHI forecast

Before you plan an outdoor activity:

look at the observed conditions to see what is happening now at your location
check the forecast maximums for the next 72 hours
review the health messages and follow the health advice for the air quality of your location

Find your local air monitoring station

Some communities have their own local air monitoring stations. Here’s how you can see the observed conditions at individual stations:

On your selected city page, choose “AQHI by Station” in the top right corner of the observed conditions section. Note: not all locations have this option.

Figure 3. Where to find AQHI by station

Long description

Air Quality Health Index for Edmonton showing an observed value of 3 in the low-risk range. A colour scale from 1 to 10+ moves from blue to dark red, with the marker placed over the number 3. The page includes links to "Past 24 hr" and "AQHI by Station", with health guidance for at-risk and general populations below.

This will bring you to a new page where you will see the AQHI values measured at all the stations in your community. Click on any of the station names to see the AQHI for the past 24 hours.

Figure 4. Sample AQHI values for air quality monitoring stations in Edmonton

Long description

Air Quality Health Index by station for Edmonton, showing a colour scale from 1 to 10+ and observed values at monitoring locations. The main Edmonton station reports a value of 3, Edmonton East reports 2, Edmonton Lendrum reports 2, Edmonton McCauley reports 3, and Woodcroft shows 3.

Changes to the AQHI forecast

The AQHI forecast may change if:

we expect conditions to be significantly different from those originally forecasted
public safety is at risk or public inconvenience will be extensive
the AQHI value rises or falls two or more index values on the AQHI scale and we expect the AQHI to stay at the new value for four hours or more

Forecast locations

Our forecast locations represent cities, communities and municipal boundaries. We use local terrain, land cover and population patterns to define these locations. You can find all the official place names in the Canadian Geographical Names Database.