Air quality forecasts are updated every business day, Monday through Friday, typically around 9 a.m. If there are air quality impacts over the weekend or on a holiday, forecasts may be updated.

The forecasts can be found on our forecast page | View >

The Air Quality Index (AQI) is a scale developed by the Environmental Protection Agency (EPA) that relates measured pollutant levels to potential health impacts. The scale is made up of six successive categories that are each associated with a color; the higher you go up on the scale, the more likely pollution could start affecting the general population. If a pollutant reaches higher than an AQI value of 100, it exceeds its federal health standard. For ozone, the AQI is based on the maximum 8-hour average of the day. For PM₁₀ and PM_2.5, the AQI is based on the 24-hour average of the day (i.e., midnight to midnight). AQI categories and corresponding ranges and colors follow:

• Good (0 – 50) — Green
• Moderate (50 – 100) — Yellow
• Unhealthy for Sensitive Groups (101 – 150) — Orange
• Unhealthy (151 – 200) — Red
• Very Unhealthy (201 – 300) — Purple
• Hazardous (301 or higher) — Maroon

ADEQ issues a High Pollution Advisory (HPA) when air quality forecasts for ozone or PM show an imminent or high probability for levels to exceed the federal health standard. HPAs encourage people to limit outdoor activities, reduce driving, and other activities that cause air pollution (leaf blowers, wood burning, etc).

ADEQ issues a High Pollution Watch (HPW) when air quality forecasts for ozone or PM show the potential for levels to exceed the federal health standard. HPWs are issued 2 to 4 days in advance and may be upgraded to a High Pollution Advisory if conditions remain favorable. HPWs give the public increased lead time to plan their actions. 

The flags indicate the forecast Air Quality Index (AQI) for the day. For ozone, the AQI is based on the maximum 8-hour average expected for the day. For particle pollution, the AQI is based on the 24-hour average expected for the day. Therefore, it is possible for there to be a period of elevated ozone or particle pollution during the day, but the AQI value remains in the Good (green) category.

On the other hand, it is possible that very high values of particle pollution are expected, enough to warrant an orange flag, but the event is expected to happen later in the day (e.g, an evening dust storm). Or, the event already took place in the morning, but is followed by good air quality the rest of the day. Another fact to keep in mind is that ozone is an invisible pollutant. Many summer afternoons appear nice, but ozone could be high.

View the hourly air quality forecast for your location for more details on what times of the day are expected to see the highest air pollution | View Forecasts >

But remember, you will fly the flag based on the daily AQI value. Simply go to the bottom of the forecast to see what color flag to fly!

Just because the colors of the flags stop at orange does not mean that the air quality is capped at the orange (Unhealthy for Sensitive Groups, or “USG”) category. It’s possible for air quality to be worse. The orange flag, which says, “High Pollution Advisory,” represents anything at the USG category or higher. View the air quality forecast for more details on the actual forecast AQI for the day | View Forecasts >

Yes. Nearby human activity (e.g., industrial processes, dust-producing activities, woodburning, etc.) or a nearby wildfire can impact your area with locally elevated levels of pollution or smoke, while other areas remain unaffected. In such cases, use your best judgment about how to modify your outdoor activities, in tandem with the forecast. If you have any questions or would like more information, you can reach out to ADEQ’s team of air quality meteorologists | Email >

No. Match the color of the flag to the Air Quality Index (AQI) category for the day.

Many air quality smartphone apps use EPA’s NowCast AQI to approximate real-time air quality conditions for a given location. However, a true AQI is a daily value, based on either the maximum 8-hour average (ozone) or the daily average (PM₁₀ and PM_2.5). ADEQ’s air quality forecasts, and therefore the flags, are based on the AQI (i.e., the daily value). More specifically, the flag represents the highest forecasted AQI category of all three pollutants for the current day.

It depends on the pollutant and the time of year.

Ozone pollution is typically higher on sunny days, between April and September, especially during the afternoon and/or early evening. Light winds and sunny skies are favorable conditions for ozone formation and build-up. Ozone can also be transported across state boundaries, depending on the weather pattern. View the hourly air quality forecast for your location for more details on what times of the day will be best for outdoor activities | View Forecast >

Particle pollution can be high at any time of the day, however, particle pollution from local sources is typically highest in the mornings and/or evenings, especially during the cooler months of the year. This is because of the “inversion,” a layer of warm air that sets in overnight and traps pollution near the ground. The inversion also causes calm winds, or “stagnation,” which allows particle pollution to build up near the ground.

Particle pollution from dust storms, on the other hand, typically occurs in the late afternoon or early evening during the monsoon season. Dust can also be transported across state boundaries from strong wind, especially in the spring and fall months. Furthermore, wildfire smoke from fires nearby or far away can result in elevated particle pollution.

Since vehicle exhaust contains particle pollution, limit activity near idling cars, buses and busy roads when possible, especially during rush hours. Also, limit outdoor activity when there is smoke or dust in the air.

There isn’t an exact amount of time. The worse the air quality, the more important it is to take breaks, participate in less intense activities, and watch for symptoms. Remember that people with asthma or other lung-related issues will be more sensitive to unhealthy air.