Sensor Data FAQ

Congratulations your AirU sensor is installed and providing measurements.  This web page provides answers to common questions about what your sensor is measuring, what it means, and how to trouble shoot the sensor.

What are the measurements and where can I view them?

Our project focuses on measuring PM2.5, and you can either view your AirU’s data through a Grafana interface (example below) or a map visualization (or both). The map can be found at on the homepage of AQandU’s website. Both interfaces display PM2.5 mass concentration in ug/m3 over time *. The map displays colored dots, and each dot is a sensor. If you have requested your dot to be hidden, it will not be displayed on the map.  However, you can search for it using the 3-digit PM sensor id.  You can find this on the back of your sensor (S-A-XXX).

Example of Grafana Web Interface

What are the health effects of PM2.5 at different concentrations?

To understand the potential health impacts of PM2.5 concentrations, you can use the following EPA guidance. 24-hour average PM2.5 concentrations greater than:

  •  35 ug/m3 are considered unhealthy for sensitive groups
  •  55 ug/m3 are considered unhealthy
  •  150 ug/m3 are  considered very unhealthy

You can get more information the health effects of PM2.5 on EPA’s AirNow site.  The dots on the map use the EPA’s color classification scheme. The dot’s color updates every 1 minute, showing the latest measured value by that sensor. The EPA’s air quality index classification for PM2.5 is based on 24-hour average readings, so the colors displayed on the map are for illustration purposes only.

Are you providing raw data or corrected data?  If it is being corrected why and how are you correcting it? 

The AirU and the PurpleAir data in the map are corrected to provide our best estimate of actual PM2.5 concentrations. We have co-located four PurpleAir network sensors with the Utah Division of Air Quality’s federal reference measurements of PM2.5 concentrations during the winter of 2016 and 2017.  From this data, we developed correction factors for the PurpleAir sensors during the winter season.  The AirU network sensors were calibrated in house with ammonium nitrate.  If you examine a filter collected during a winter-time inversion, you would find that ammonium nitrate contributes the majority of the PM mass on that filter.  Thanks to the Division of Air Quality, PurpleAir, and the graduate student who calibrated all of the PM sensors in the AQandU network.  You can see the corrections below.

AirU Sensor correction relationships for winter.

Sensor Slope Intercept Calibration/range (ug/m3)
AirU 0.851 1.1644 Laboratory, 0 – 200


  • Corrected PM2.5 (ug/m3) = Sensor raw value * slope + intercept.
  • The calibration range is the range of the raw sensor reading.
  • When the AirU sensors exceed the upper limits of the calibration ranges, the corrections are highly uncertain.
  • Individual sensor performance may vary.

How will I know if my sensor is malfunctioning, and what should I do if it is?

What if:

  • My sensor goes offline?
    • Ensure that your sensor has power. If not, provide power.  If it has power unplug it for 10 seconds, and plug it back in.  If it continues to read zero, contact us.
  • My PM2.5 concentrations are 0 ug/m3 for more than 48 hours?
    • Ensure that your sensor has power.  If not, provide power.  If it has power unplug it for 10 seconds, and plug it back in.  If it continues to read zero, contact us.
  • My PM2.5 concentrations remain constant (i.e., 4 ug/m3) for more than 24 hours?
    • Unplug your sensor for 10 seconds, and plug it back in. If the numbers still do not change, contact us.
  • My PM2.5 concentrations fluctuate by more than 50% on a minute-by-minute, basis?
    • PM2.5 levels can fluctuate greatly on a minute-by-minute basis.  Although we are interested in minute-by-minute readings, we are more interested in hourly and daily averages.  It is more important to determine if your sensor generally follows air quality trends.
  • My PM2.5 concentrations show an unhealthy level > 150 ug/m3 that lasts for a few minutes?
    • This can be normal, and there may be many causes.  One larger particle may have passed through the sensor and provided an erroneous reading, or a malfunctioning vehicle/an individual smoking a cigarette may be near the sensor.
  • My PM2.5 baseline drifts?
    • Baseline drift is when your PM sensor should read close to zero, but it actually reads 15 or 20 ug/m3.
Example of Baseline Drift: As time goes on, 1003-1 (Blue) deviates from the baseline, TOEM (Black), while 1003-2 (Purple) stays with the baseline

If I have a Grafana web page, what does average, min and max mean?

If we set up a Grafana webpage for you, you may see three numbers: min, max, and average.  Above these numbers you will see an averaging time, and you can change this averaging time to whatever you like.  We suggest 24 hours.

  • Min is the minimum 1 minute PM2.5 concentration over your averaging period. This number is not very meaningful.
  • Max is the maximum 1 minute PM2.5 concentration over your averaging period. his number is not very meaningful.
  • Avg is the average PM2.5 concentration over your averaging period.  This is a useful measure.

We are working on mapping/better interfacing tools, and the screen you see is just a starting point.



*PM2.5 is the mass of particulate matter that is smaller than 2.5 um in diameter, and it is about 1/10th the size of a human hair.  This is one of the key pollutants that the US EPA measures because of its potential for adverse health effects, and the Wasatch Front experiences elevated levels of PM2.5 during our wintertime inversions as well as periodically because of dust storms, wild-fire and fireworks.

If you have additional questions, please contact us.