Large circles on the map show Air Quality Index (AQI) values — for ozone and AQI2.5 — as measured at official, outdoor permanent monitoring sites managed in the Bay Area by the Air Quality Management District and submitted to the U.S. EPA’s AirNow database. Data from these sensors is updated hourly.
Smaller squares show real-time PM2.5 readings at low-cost, individually owned PurpleAir sensors that may be located indoors or outdoors. Data is updated every four hours. Outliers may be a result of localized activities, such as small fires or exposure to vehicle exhaust. Alternatively, healthy air quality in an otherwise unhealthy location could be the result of a sensor placed in a well-ventilated indoor area.
Use the layer selector in the top left corner to toggle between layer views, including current wind and weather patterns, based on hourly weather station data provided by NOAA.
If the map does not display below, view it here.
Map produced by Matthew Green and Brendan Soulé
What does AQI Mean?
The Air Quality Index (AQI) is a scale used to measure and report air pollution levels. It tells you how clean or polluted the air is and what health effects might be a concern. Generally, AQI values above 100 are considered unhealthy. Specifically, values between 101-150 are unhealthy for sensitive groups (like children, older adults, and people with heart or lung disease), 151-200 are unhealthy, 201-300 are very unhealthy, and anything over 300 is considered hazardous. When the air quality is poor (AQI above 100), it’s best to limit prolonged or strenuous outdoor activities. Sensitive groups should be especially cautious and may need to stay indoors. Checking the air quality forecast can help you plan your activities accordingly.
Want more information about air quality and wildfire smoke?
- How to protect yourself from wildfire smoke
- How to read air quality maps properly, from Purple Air to AirNow
- Masks for smoke and COVID: Which are best?
Here is an expanded list of other air quality measurement resources:
- U.S. Forest Service Air Monitoring Program
- Air Resource Board Breathewell for Mobile
- World Air Quality Index
AirNow is also running a project that adds data from low-cost sensors to a fire and smoke map.