From "Good" to "Hazardous": Decoding the Air Quality Index

A lot has been said in recent weeks about the Air Quality Index (AQI). What does this rating mean, and how can you decode the various levels to determine your specific risk at any given time? Here is what you need to know to protect your health.

Understanding How to Interpret the AQI

As millions of Americans have learned recently, wildfire season is starting to ramp up across North America. Dozens of U.S. cities were under a thick cloud of dangerous smoke recently when hazy air from fires burning in Canada wafted over the border. Several of the country's most populated urban areas saw air quality readings soar to hazardous levels.

Understanding the AQI is imperative if your community is experiencing any degree of smoke or haze from wildfires. This system is used by the U.S. Environmental Protection Agency (EPA) to convey outdoor air quality. The system helps people understand complex pollution data, putting the metrics into an easy-to-understand and actionable format. The standardized system gives laypeople the information they need in one glance to determine if the air is healthy to breathe at that specific time.

Wildfires are not the only cause of poor air quality conditions. The increased industrialization around the world has inherently added more pollution to the air. When paired with the uptick of extreme climate events due to global warming, it is more important than ever for officials to monitor the AQI and disseminate that information to the public.

The EPA updated its metric for the AQI system a few years ago. The AQI measures the five known major pollutants that are regulated by the U.S. Clean Air Act. The five pollutants are ground-level ozone (O₃), particle pollution (PM₂.₅ and PM₁₀), carbon monoxide (CO), sulfur dioxide (SO₂), and nitrogen dioxide  (NO₂).

Each of these five pollutants is assigned an index value based on measurements at designated monitoring stations. The highest value indicates the overall AQI.

An AQI of 0 - 50 (green) is considered "good," meaning that the air quality does not pose any dangers. A score of 51 - 100 (yellow) is "moderate," signaling that while air quality is acceptable, some sensitive groups may experience slight issues. An AQI rating of 101 - 150 (orange) is "unhealthy for sensitive groups."  A rating of 151 - 200 (red) falls under the designation of "unhealthy." At this stage, some members of the general public may experience difficulties breathing or other symptoms, such as itchy eyes or throat irritation.

Climbing up the ladder, an AQI of 201 - 300 (purple) is listed as "very unhealthy." The health risks for all individuals are elevated at this level. A rating of 301 or higher (maroon) is "hazardous," accompanied by the warning that everyone is likely to be significantly affected.