How can I read the air quality index? And how to know when it's unsafe to be outside during a heat wave or warning

As temperatures climb across Canada, so do levels of air pollution. Here's how to stay safe when the air quality becomes poor.

This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis or treatment. Contact a qualified medical professional before engaging in any physical activity, or making any changes to your diet, medication or lifestyle.

Smoke and ash particles creating eerie sun glow in San Francisco Bay Area.
How do you know when the air quality is considered unsafe to be outdoors? (Image via Getty Images)

With most of central and eastern Canada under an extreme heat advisory, millions are advised to be on alert for any heat-related illnesses like heat exhaustion and heat stroke. But just like wildfires, soaring temperatures can also compromise air quality, which puts people with chronic health conditions at risk.

How do you know when the air quality reaches potentially harmful levels? Keep reading to learn more about air quality, reading air quality indexes and how to protect yourself when air quality is poor.

☀️ How does heat impact air quality?

As temperatures rise, air pollution increases — especially for people in urban centres.

Heatwaves or periods of extreme heat initiate chemical reactions that turn nitrogen oxides emitted from automobile engines and other pollutants (like volatile organic compounds) into ground-level ozone, one of the main ingredients in smog.

🚦 How do you know if air quality is safe?

The Air Quality Health Index (AQHI) is a scale from 1 to 10 that measures air quality. Canadians are encouraged to use the AQHI to help them make decide whether or not they should limit their time outdoors or adjust their activity levels during periods when the AQHI is high.

The AQHI includes the following categories along with some suggestions for people who are considered at-risk for respiratory issues and the general public. The AQHI does not measure the effects of pollen, odour, dust, heat or humidity.

Young unhealthy female sit on couch having difficulty breathing pain of heart, touches his chest with hand. Trouble breathing, chest pain. Heart attack, thoracic osteochondrosis, panic attack concept
A high air quality health index could potentially cause health issues for at-risk populations. (Image via Getty Images)

🟢 1-3 Low health risk

When AQHI is low, the air quality is considered ideal for both at-risk populations and the general population to enjoy outdoor activities.

🟡 4-6 Moderate health risk:

For at-risk populations, the AQHI suggests restricting or limiting strenuous outdoor activity if they are experiencing symptoms. The AQHI is considered safe for the general public, unless they are experiencing symptoms like an irritated throat or cough.

🔴 7-10 High health risk

When AQHI is high, at-risk populations, including children and the elderly, are advised to reduce or reschedule strenuous activities. The general population is encouraged to consider reducing strenuous outdoor activities if they begin experiencing symptoms like coughing and throat irritation.

🚨 10+ Very high health risk

A ‘Very High’ AQHI, at-risk populations (including children and the elderly) should avoid outdoor activities and outdoor physical exertion. The general population is advised to reduce or reschedule strenuous outdoor activities, especially when symptoms occur.

🔍 How do I check the AQHI?

If you have a smartphone, the AQHI should appear on your Weather app — and adjust to your location and the scale it uses.

You can visit the Government of Canada's website to check your local AQHI.

How AQHI appears on an iPhone's Weather app.
How AQHI appears on an iPhone's Weather app.

If you're looking for an air quality index map, IQAir, a Swiss technology company, offers an interactive global map. However, the map uses different index values to measure air quality than the 1-10 scale used in Canada.

⚕️How does air quality impact our health?

Air pollutants act as irritants to our lungs. On days with poor air quality, people are more likely to experience shortness of breath, difficulty breathing and coughing or wheezing — especially if they have a chronic respiratory disease like asthma or chronic obstructive pulmonary disease (COPD).

U.S. National Institute of Environmental Health Services, long-term exposure to air pollution can reduce lung function and contribute to the development of conditions like emphysema, chronic bronchitis and COPD. It's also been associated with non-Hodgkin’s Lymphoma, lung cancer and has been associated with an increased risk for breast cancer.

Sick elderly man makes inhalation
Poor air quality can be dangerous — especially for people with chronic respiratory conditions. (Image via Getty Images)

A study published in 2023 found that heatwaves increased levels of air pollution and extreme heat increased the risk of heart attack for women and older adults.

😷 What can I do to protect myself when air quality is poor?

The best thing you can do when air quality is poor is avoid the outdoors as much as possible. The American Lung Association recommends keeping your windows closed and opt for air conditioning on the recirculate setting (if you have access to air conditioning). HEPA air filters can also be beneficial for at-risk groups. If you do have to go outside, consider wearing an N95 or KN95 mask to help filter airborne particles.

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