Using Air Quality Sensors for Smoke: Understanding Sensor Data
During smoke events, air quality sensors can provide localized information about outdoor and indoor air quality. Air sensors may help you make decisions about where to spend time or when to go outside when wildfire smoke is affecting your area. They may also help you understand how to reduce your smoke exposure indoors. This fact sheet focuses on the use of sensors to measure fine particulate matter (PM2.5), because it is one of the main pollutants in wildfire smoke. See the What to Consider Wildfire Guide fact sheet for information about choosing and placing air sensors
On this page:
- How You Can Use PM2.5 Sensor Data
- Understanding Sensor Data Quality
- Correcting PM2.5 Sensor Data
- Resources
How You Can Use PM2.5 Sensor Data
These simple approaches can help you understand your PM2.5 sensor data:
- Examine trends over time in one location—Sensor data can help you see when PM2.5 levels are starting to get better or worse in real time. For example, you can see:
- How much PM2.5 levels drop when you use a portable air cleaner or run your central air system with a higher-efficiency filter.
- How activities in your home can contribute to increased PM2.5 levels (e.g., burning candles, cooking).
- Compare PM2.5 levels in different locations—Sensor data can help you compare PM2.5 levels in different locations. For example, you can:
- See whether PM2.5 levels are lower indoors or outdoors.
- Compare PM2.5 levels in different outdoor locations.
- Identify which room in your house has the lowest PM2.5 levels.
Try to compare data from sensors of the same type using the same units (for example, particle mass, number, or air quality index). If PM2.5 levels are trending higher at your location, take steps to reduce your exposure. Learn more in our other Wildfire Guide Fact Sheets.
Understanding Sensor Data Quality
PM2.5 sensors have a higher level of uncertainty and may not give the same readings as the highly accurate PM2.5 regulatory monitors typically used by state, local and Tribal air agencies. They can also be affected by unrelated interferences, such as fog, relative humidity, and temperature.
PM2.5 sensors are good for measuring smoke particles nearby, but they do not measure visible smoke high in the sky, visible large ash on surfaces, or gases.
Trust your senses. If you are experiencing health effects from smoke, take action to reduce your exposure, regardless of what a sensor is reading.
Checking the Quality of Your Sensor Data
For outdoor sensors, comparing your sensor’s data to data from other sensors or reference monitors nearby can indicate how well your sensor is working. While they may not report the same values due to highly localized sources, different data corrections, or error, they should show similar trends over time.
Recognizing Problems With Sensor Data
Air sensors sometimes fail, and you may not notice the failure right away. Routinely review your data to help identify these common problems with PM2.5 sensors:
- Suspicious data. Values that do not change (stuck data), sudden frequent jumps in the data, or suddenly very erratic data may indicate a problem.
- Consistently very low values. If the sensor reports very low values, you may not be able to tell whether this is accurate or a sensor malfunction. You can do a simple test to see if the sensor is responding, such as safely lighting a match nearby.
- Large differences in duplicate measurements. Some sensor products report data from two sensors in the same unit. You can compare the data to make sure they both respond similarly.
- Declining performance over time. Sensor readings may become less accurate when sensors have been in operation for a long time or during high PM2.5 levels.
If you notice a problem with the data from your air sensor, consult the manufacturer’s recommendations for troubleshooting or replacing the device.
Correcting PM2.5 Sensor Data
Uncorrected sensor data can be useful for detecting trends or comparing PM2.5 levels in different locations.
Correction equations, including equations specifically for smoke, may be available for some sensors. Applying these equations can improve the accuracy of the sensor data. For example, AirNow applies an EPA correction equation before showing sensor data on the Fire and Smoke Map.
Note: Air sensors typically report pollutant levels every few seconds or minutes. Use caution if comparing these very short-term sensor readings directly to the National Ambient Air Quality Standards (NAAQS) or the U.S. Air Quality Index for PM2.5, which are based on 24-hour averages. For the official data used to determine compliance with the PM2.5 NAAQS, visit EPA Air Quality Design Values.
Resources
Information on Air Quality
Check out the AirNow Fire and Smoke Map, your state air quality website, or your local news for air quality information. Access these resources using the links below.
- AirNow Fire and Smoke Map
- Wildfire Guide Fact Sheets
- Resources and Information on Wildland Fires and Smoke
- Infographics on Staying Safe Before, During and After Fires
