What Is an Air Quality Warning?
An Air Quality Warning is an alert that indicates poor air quality is expected or occurring and may pose a significant risk to health. Air quality can deteriorate because of wildfire smoke, urban pollution, industrial activity, or a combination of pollutants.
In Canada, air quality health risks are communicated using the Air Quality Health Index (AQHI), which ranges from 1 to 10+. Higher values indicate a greater potential health risk from air pollution.
Air quality warnings and other air quality alerts help people determine when they should reduce their exposure to polluted air, particularly people who are more susceptible to its health effects.
Related Warnings
| Warning or Alert | Description |
|---|---|
| Yellow Air Quality Warning | Indicates elevated air pollution that may pose a greater health risk, particularly for people who are more susceptible to air pollution. |
| Orange Air Quality Warning | Indicates very poor air quality and a higher health risk that may require people to significantly reduce or reschedule outdoor activities. |
| Special Air Quality Statement | May be issued to provide information about deteriorating air quality, including conditions caused by wildfire smoke. |
When Is an Air Quality Warning Issued?
An Air Quality Warning is issued when air pollution is expected to rise to levels that present a significant health risk.
Environment and Climate Change Canada uses the Air Quality Health Index (AQHI) and air-pollution forecasts to determine the potential health risk and appropriate alert level.
The AQHI health-risk categories are:
- 1–3: Low risk
- 4–6: Moderate risk
- 7–10: High risk
- 10+: Very high risk
Air quality alerts may be triggered by elevated concentrations of pollutants such as fine particulate matter (PM2.5), ground-level ozone and nitrogen dioxide. Wildfire smoke can cause especially rapid changes in PM2.5 concentrations and the AQHI.
The exact alert issued can depend on the severity, cause, duration and expected health impacts of the poor air quality.
What Weather Conditions Should You Expect?
Conditions during an Air Quality Warning depend on the source of the pollution. During wildfire smoke events, you may notice hazy or smoky skies, reduced visibility and the smell of smoke.
Poor air quality is not always obvious, however. Harmful pollutants can be present even when the sky appears relatively clear.
Weather conditions can also influence how pollution behaves. Light winds and stagnant atmospheric conditions can allow pollutants to accumulate, while stronger winds may disperse pollution or transport wildfire smoke into a region from fires hundreds or even thousands of kilometres away.
During an Air Quality Warning, monitor the AQHI and local air quality alerts rather than relying only on how the sky looks or smells.
What Should You Do During an Air Quality Warning?
Check your local AQHI regularly and follow the health recommendations included with the warning.
When air quality presents a high or very high health risk:
- Reduce or reschedule strenuous outdoor activities when recommended.
- Spend more time indoors when outdoor air quality is poor.
- Keep windows and doors closed when outdoor smoke or pollution levels are high, if indoor conditions allow.
- Pay attention to symptoms such as coughing, throat irritation, wheezing, shortness of breath or chest discomfort.
- Take additional precautions if you are more susceptible to air pollution.
- Follow instructions from local health and emergency officials.
When the AQHI reaches 10+, the health risk is considered very high and everyone can be affected by air pollution. People who are more susceptible to air pollution should take particular care to limit exposure.
Frequently Asked Questions
An air quality warning is issued when pollution levels become high enough to pose a risk to human health. These warnings often occur during wildfire smoke events or periods of elevated ozone and particulate matter, and they encourage people to take steps to reduce their exposure.
It depends on the severity of the warning and your health. Healthy people may be able to spend short periods outdoors, but prolonged or strenuous activity should be reduced when air quality is poor. Children, seniors, pregnant individuals, and people with heart or lung conditions should take extra precautions and limit outdoor exposure.
Air quality warnings are most commonly caused by wildfire smoke, high levels of fine particulate matter (PM2.5), ground-level ozone, vehicle emissions, industrial pollution, and weather conditions that trap pollutants near the ground.
Common symptoms include coughing, sore throat, irritated eyes, headaches, wheezing, chest tightness, and shortness of breath. People with asthma, COPD, or heart disease may experience more severe symptoms.
An air quality warning can last anywhere from a few hours to several days, depending on the source of the pollution and weather conditions. Changes in wind direction or rainfall often help improve air quality, while ongoing wildfire activity may prolong the warning.
Reduce time spent outdoors, avoid strenuous exercise, keep windows and doors closed when smoke is present, use an air purifier if available, and monitor official Air Quality Health Index (AQHI) updates until conditions improve.
