Air quality and pollen, explained
Many weather apps show an air quality number and a pollen level beside the forecast. This guide explains both. It is general information, not medical advice.
The air quality categories below come from AirNow, the United States government’s air quality service, and were checked on September 19, 2026. See AQI basics.
The air quality index
The air quality index, or AQI, runs from 0 to 500 and is divided into six categories.
| Range | Category | What AirNow says |
|---|---|---|
| 0 to 50 | Good | Air quality is satisfactory and air pollution poses little or no risk |
| 51 to 100 | Moderate | Acceptable, but there may be a risk for people unusually sensitive to air pollution |
| 101 to 150 | Unhealthy for sensitive groups | Members of sensitive groups may experience health effects |
| 151 to 200 | Unhealthy | Some members of the general public may experience health effects |
| 201 to 300 | Very unhealthy | The risk of health effects is increased for everyone |
| 301 and above | Hazardous | Emergency conditions and everyone is more likely to be affected |
AirNow uses the phrase sensitive groups for people who are affected first when air quality declines, and points to its activity guides for what to do at each level.
Where the number comes from
The AQI is based on measurements of several pollutants, including fine particles and ozone. Wildfire smoke raises the particle reading. Hot, still summer days raise the ozone reading. The number changes through the day, so a morning reading can differ from an afternoon one.
Pollen
A pollen forecast estimates the amount of tree, grass, or weed pollen in the air, usually as low, moderate, high, or very high. Pollen is highest on dry, breezy mornings and lowest after rain. The type of pollen changes with the season, with trees in spring, grass in early summer, and weeds in late summer and autumn.
In Canada
Canada uses the Air Quality Health Index, a scale from 1 to 10 and higher, with its own categories. See the Air Quality Health Index page.
What this means for Bold Weather
Bold Weather does not show air quality or pollen, because the weather service it uses does not provide them. The built-in Weather app on iPhone shows the air quality index where it is available. Bold Weather keeps to the temperature, the forecast, alerts, and the UV index. Explore the details screen or learn about the TestFlight beta.