AirU Sensor

The sensor is about 4”x 4”x 4” and weighs ¼ lb with the housing. 

The AirU can hang from a hook under an overhang (like a plant), or mounted on a wall, like a smoke detector.

Ideally, the sensor should be mounted in a protected spot outdoors, like under an eave. Your sensor needs a strong Wi-Fi signal ( a minimum of 2 bars on a mobile device ). The AirU’s protective housing is water resistant but not water proof. The AirU should be roughly breathing level (5 ft high or higher). Avoid placing it near kitchen exhaust or dryer vents or less than 4 ft above the ground. The sensor needs to connect to power.

The AirU consumes approximately 1.5 Watts.  The cost of power varies by location, but it will cost less than 1 cent per month.

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 does not come back online contact us at contact@tetradsensors.com.
  • 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 contact@tetradsensors.com.
  • 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 contact@tetradsensors.com.
  • 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.  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.


The AirU works only with personal 2.4 GHz networks. 

The AirU device needs a strong (more than 1 bar) 2.4 GHz WiFi signal.  It cannot use a captive portal (i.e., network that requires manual acceptance of terms through an HTML page before allowing access, like hotels or airports).  It is not capable of WPA-Enterprise, where a certificate and/or username is needed to connect. The system administrator may need to allow access to the device’s mac address (posted on the outside of the housing and the board itself). 

The AirU communicates with the following endpoints, which must be open:

  • mqtt.2030.ltsapis.goog:8883    – data packets every 2 minutes
  • time.google.com:123
  • ota.tetradsensors.com:443– Over-the-Air firmware updates

This is actually a really challenging question, and researchers are actually evaluating this.  This depends on what types of questions you are interested in answering and the topography and meteorology of your area.  In our experience (mountain valley), we were able to capture significant differences how sensors correlate with each other for particulate matter concentrations associated with a variety of pollution events (“inversions”, wildfires, and fireworks) at spatial distances of one sensor per 1.5 to 2.5 mi2 and elevation differences ranging from 200 to 400 ft.  

The AirU has safety features in place which will prevent you from easily connecting the device to a new WIFI network, after it has already been connected. To connect the device to a new WIFI network, unscrew the four housing screws on the back of the AirU and separate the housing to expose the red PCB. Next, while the AirU is powered, press and release the RELOAD button, which is the button located closest to a corner of the PCB, and highlighted in the image. The WIFI credentials from the previous network have now been erased from the device, and it will now appear on the Tetrad Connect app for provisioning. 

AirU Map

The AirU map displayed in tetradsensors’s home and dashboard page is populated with icons representing public sensors. We currently display 2 type of sensors, AirU’s and PurpleAir sensors. Their color on the indicates their PM2.5 reading on the US EPA Air Quality Index scale from the last 15 to 30 minutes. Sensors that appear with a grey color didn’t return a PM2.5 value in the last 15-30 minutes.

Colormap overlays are modelisation of PM2.5 real time measures in specific areas where we do have enough sensors to extrapolate their data to nearby areas.

Map overlays are only available in an area where we have sufficient number of sensors.

Data Access

The table below list the file you can access through the website by clicking on data file links.

Data FileCorrection FactorsFormatDescription
AggregatedDataAppliedJsonContains averaged PM2.5 for each sensor displayed on the map within the last 15 minutes.
GetSensorsDataNot AppliedJsonContains all sensors PM2.5 reading within the last 15 minutes.
WeeklyMapsAppliedJpegArchive that contains weekly processed maps for each city.
LatestMapsAppliedJsonArchive that contains the latest unprocessed map (raw json file) for each city
Correction factorsNot ApplicableJsonContains the correction factors we are using to correct PM2.5 readings.

You can also download the data from your local dashboard in google datastudio or through our api, which you can find the related documentation here.

In the website dashboard, the time zone is UTC, coordinated universal time.

In the data studio, the timezone is local.

To create a “nickname” for your device, you can use the following URL:


Be sure to URL-encode your nickname string before you call this URL. URL-encoding is the act of replacing characters that are not allowed in a URL with characters that are allowed. For example, a space is replaced with %20. You may use the following website to encode the nickname parameter: 


For example, if you want to give the device 30F5205BF383 the nickname “Geirge T. Craig Air Quality Monitoring Site”, you would pass that phrase through the website’s encoder and it returns:


And the final URL to set it up looks like:


Just put this link into your browser and hit Enter, it’s name should be updated in the data studio after a reload.