Just as alerts are given when threatening weather is approaching, air quality alerts are official notifications issued when pollution levels in the air we breathe reach unhealthy thresholds.

These alerts are designed to inform the public, especially those with health sensitivities, about when outdoor air may pose a risk to breathing or overall wellness. The alerts are based on the Air Quality Index (AQI), a color-coded scale developed by the U.S. Environmental Protection Agency (EPA) that ranges from 0 to 500, with higher numbers indicating worse air quality.

Air quality alerts are often triggered by pollutants like ground-level ozone, particulate matter (PM2.5 and PM10), carbon monoxide, and nitrogen dioxide. In the summer months, alerts are commonly issued due to high ozone levels caused by the reaction of sunlight with vehicle emissions and industrial pollutants. During wildfire season, fine smoke particles can also lead to widespread alerts, even in areas very far from active fires.

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The severity of an alert depends on how high pollutant levels climb. For example, an AQI in the "Unhealthy for Sensitive Groups" (orange) category may affect children, the elderly, and people with respiratory or heart conditions. As the levels move into "Unhealthy" (red) or "Very Unhealthy" (purple), the risks extend to the general population, and everyone is advised to limit outdoor activity, regardless if you have a respiratory condition or not.

When an air quality alert is in effect, it's best to stay indoors with windows closed, use air purifiers if possible, and avoid strenuous outdoor exercise. Checking your local AQI on weather.com or public health agencies before you plan your day, especially during high-risk seasons like summer heat waves or wildfire outbreaks.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.