What Is an Orange Air Quality Warning?
An Orange Air Quality Warning is issued when air pollution is expected to reach, or has already reached, very high levels. In Ontario, this warning is issued when the Air Quality Health Index (AQHI) is forecast to reach or has reached 10+, indicating a very high risk from air pollution. People are advised to limit strenuous outdoor activities and follow local public health guidance.
What Does an Orange Air Quality Warning Mean?
An orange warning indicates that poor air quality could have significant effects on people across the affected region. It is more serious than a yellow warning and may be issued during periods of heavy wildfire smoke or unusually high air pollution.
Environment and Climate Change Canada uses colour-coded alerts to communicate the expected severity of weather and environmental conditions. Orange alerts generally indicate major or widespread impacts.
Air quality warnings are based partly on the Air Quality Health Index, which measures the potential health effects of air pollution on a scale from 1 to 10+.
Air Quality Health Index Levels
| AQHI | Risk Level |
|---|---|
| 1–3 | Low |
| 4–6 | Moderate |
| 7–10 | High |
| 10+ | Very High |
Air Quality Warning Levels
| Yellow Warning – Air Quality | AQHI of 7–9 |
| Orange Warning – Air Quality | AQHI of 10+ |
In Ontario, orange air quality warnings are associated with the very high-risk category of 10+. Elsewhere in Canada, alert colours also take into account the expected impacts of an event.
What Causes an Orange Air Quality Warning?
Orange air quality warnings can be issued when high concentrations of pollutants develop in the atmosphere. These pollutants may come from several sources, including:
- Wildfire smoke: Smoke from forest fires can travel hundreds or thousands of kilometres, affecting communities far from the fires themselves.
- Vehicle emissions: Exhaust from cars, trucks and other vehicles contributes to air pollution, particularly in busy urban areas.
- Industrial emissions: Factories, power plants and other industrial operations release pollutants into the atmosphere.
- Ground-level ozone: This pollutant can develop when emissions react in sunlight, particularly during hot summer weather.
Wildfire smoke is an important cause of severe air quality events in Canada. It contains fine particles known as PM2.5, which can remain suspended in the air and be inhaled deep into the lungs.
What Should You Do During an Orange Air Quality Warning?
When an orange warning is issued, Environment and Climate Change Canada and public health authorities recommend taking precautions to reduce exposure to outdoor air pollution.
Recommended steps include:
- Limit strenuous outdoor activities. Consider postponing running, cycling, outdoor sports or physically demanding work until conditions improve.
- Keep windows and doors closed when practical. During wildfire smoke events, this can help reduce the amount of outdoor smoke entering your home. If indoor temperatures become dangerously hot, prioritize staying cool.
- Use indoor air filtration if available. Portable air cleaners with suitable particle filters can help reduce indoor concentrations of wildfire smoke.
- Check local air quality readings. Monitor the AQHI throughout the day, as conditions can change quickly.
- Follow local public health guidance. Pay attention to recommendations from your local health authority, particularly if you have existing heart or lung conditions.
Children, older adults, pregnant people and individuals with certain medical conditions may be more affected by poor air quality.
How Long Does an Orange Air Quality Warning Last?
There is no fixed duration for an orange air quality warning. It remains in effect while the conditions that prompted the warning continue to pose a concern.
Some warnings may last several hours, while others can continue for multiple days.
The duration depends on factors such as wind direction, changing weather patterns, wildfire activity and how quickly pollutants disperse.
Air quality readings can also change throughout the day. A temporary improvement does not necessarily mean the warning has ended.
Frequently Asked Questions
In Ontario, a yellow air quality warning is issued when the AQHI is forecast to reach 7 or higher, indicating high risk. An orange warning is issued when the AQHI is expected to reach or has reached 10+, indicating very high risk.
You can still go outside, but limiting your exposure to polluted air is recommended. People at higher risk should avoid strenuous outdoor activities, while others should reduce or reschedule demanding activities, particularly if they experience symptoms.
No. Although wildfire smoke can cause severe air pollution, high pollutant concentrations from other sources, including industrial activity and vehicle emissions, can also contribute to poor air quality.
You can check current warnings and local AQHI readings through Environment and Climate Change Canada, the WeatherCAN app or your provincial air quality monitoring service.