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AirU Sensor

A significant portion of air pollution is attributed to PM2.5, a reliable indicator of overall air quality. Communities have expressed growing interest in gaining insights into the various pollutants contributing to their Air Quality Index (AQI). To address this demand, we introduced the AirU Pro, designed with a modular approach to provide comprehensive air pollution exposure information.

While the AirU+ suits the needs of many individuals, delivering valuable data on PM2.5 (with the option for PM10), the Redox sensor effectively detects changes in NO2, albeit in a voltage signal format rather than specific units of measurement.

While the AirU Pro may seem robust for individual use, it’s a popular choice among our customers. Its modular platform allows users to expand their monitoring capabilities to include pollutants comprising the AQI (PM, O3, CO, SO2, and NO2), as well as other substances relevant to scenarios like water treatment, construction dust, or refinery operations. Additionally, the Pro model offers enhanced communication options, including LTE connectivity.

The AirU+ is a highly capable air monitoring solution, especially if your primary focus is on monitoring PM2.5, and you have access to Wi-Fi and a power source. In this scenario, the AirU+ is a sensible choice.

Looking ahead, we are in the process of developing a new indoor monitor that will feature CO2 measurement capabilities and sport a sleek, indoor-friendly design. Alternatively, the AirU Pro, equipped with CO2 monitoring, can be an excellent choice for indoor air quality assessment.

AirU Legacy Sensor dimensions: 4” x 4” x 4”.

AirU+ Sensor dimensions: 4.7″ x 4.7″ x 2.4″.

AirU+ PM10 Sensor dimensions: 7.9″ x 4.7″ x 3.6″.

AirU Pro Sensor dimensions: 7.6″ x 5.3″ x 3.6″.

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 info@tellus.
  • 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 info@tellus.
  • 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 info@tellus.
  • 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.

Communities can collect spacially dense air quality measurements by having community members host sensor nodes, provide power, and connectivity (often WiFi). These sensor nodes push measurements to a cloud database where they are quality assured and can be visualized on a map and/or downloaded. Once a critical mass of sensors is deployed, these measurements can be integrated (see example). These visualizations can help communities make sense of the somewhat imperfect data from the sensors. Each sensor node may measure multiple pollutants, although particle pollution, a key driver of adverse health effects, is a common air-quality indicator and can (with proper quality control) provide good estimates of air quality. Depending on the pollutants being measured, sensor nodes typically cost hundreds to a few thousand dollars.

Regulatory measurements must meet strict siting and quality control standards, and they require dedicated maintenance. This equipment typically costs thousands to tens of thousands of dollars per pollutant. Its level of expense and quality control is required for regulatory purposes.

Data quality is one of the biggest challenges with crowd-sourced sensor measurements. The sensors can malfunction or located indoors rather than outdoors. Some pollutant measurements are sensitive to environmental conditions (i.e., temperature, humidity and composition of the species in the air). It is critical for malfunctioning sensors and to develop appropriate corrections for the environment. These corrections typically rely on state and regulatory agencies that allow co-location of the crowd-sourced sensor node with their high-quality regulatory monitors.

Crowd-sourced air quality measurements are typically presented as dots on a map, but this can be difficult to make sense of. Oftentimes, sensors in close proximity may read disparately, which may reflect reality or malfunctioning sensor nodes. One way to improve this difficult-to-interpret data is to incorporate the screened and environment-corrected measurements into a regression model, with appropriate functions s for distance, time and elevation to obtain continuous-valued spatio-temporal estimates of air quality throughout a region (see example).

Low-cost PM sensors use a laser scattering principle, which works by using a laser to radiate suspended particles in the air. The scattered light is then collected by an internal photodiode, and finally the curve of scattering light change with time is obtained. Finally, equivalent particle diameter and the number of particles with different diameter per unit volume can be calculated by microprocessor based on MIE theory (link).

The conversion from total light scattering to particle concentration measurements are based on the size of the particles and the number of particles passing through the laser, but also the optical properties of the particles. Different types of particles may scatter light in different ways due to their shapes or chemical makeup, which affects the amount of light received by the photodiode and ultimately the final concentration measurement. For example, optical PM sensors typically overestimate concentrations of wildfire smoke or pollution from wintertime inversions, but tend to underestimate firework smoke, sometimes by as much as 2x! Other environmental parameters such as humidity can have a profound impact on the sensor measurements as well. Therefore it’s very important to ensure that we keep the sensor calibrations up-to-date depending on the makeup of the current environment.

Our team takes care to calibrate each sensor in our lab. The PM2.5 sensors are quite stable and hardly change over their lifetime since they’re optical sensors. However, our gas sensors can drift a bit after about a year or so, and we generally recommend replacing them within 18 to 24 months.

We offer seasonal calibration updates, about four times a year, for our sensor network users, mainly researchers or anyone looking to fine-tune their data. It’s a service that’s typically more popular with our bigger sensor network users.

We perform multi-variable regional calibrations for all PM sensors using ground-truth data from local Federal Equivalement Method (FEM) or Federal Reference Method (FRM) sources. FEMs/FRMs are very high-quality monitoring instruments, typically maintained by the EPA, which produce reliable hourly PM concentration measurements. We collect measurements from these gold-standard sources and compare them to nearby low-cost monitors to provide accurate, up-to-date calibrations that are directly traceable to these ground-truth sources. We periodically recompute and update these calibrations to consider the latest environmental parameters of the region.

Ensuring optimal performance of your AirU unit is crucial for accurate air quality monitoring. To achieve this, it’s essential to maintain unobstructed airflow at the bottom of the unit. Both the AirU+ and Pro models rely on this unobstructed pathway for the intake and exhaust of air samples. By keeping the bottom of your AirU clear, you’re not only guaranteeing precise data but also ensuring that your investment in clean, healthy air is maximized.

The AirU monitors have a rich history rooted in outdoor applications. Originally conceived for outdoor use, these monitors have proven their resilience over more than five years of deployment in diverse regions across the United States. Notably, they have excelled in extreme conditions, from the scorching heat of Las Vegas to the freezing cold of Alaska.

Their adaptability and robust performance in challenging environments stand as a testament to their engineering excellence. While Alaska’s extreme cold presented unique challenges, no such issues have arisen elsewhere, reaffirming the monitors’ reliability and effectiveness in providing accurate air quality data.

Both the AirU+ and Pro models are built to handle different weather conditions like rain, snow, and ice. They’re designed to keep water out, and the only openings are at the bottom, which is a pretty safe bet unless we’re expecting some truly strange weather where it rains upward.

They produce a bit of heat, which helps keep their electronic parts warm during chilly winter months. So, whether it’s sunny or snowy, they’ve got you covered for year-round air quality monitoring.

  1. Regarding sharing access to owned devices with additional users, the account admin can do this through the dashboard setting functions. 
    1. Log into your dashboard at airview.tellusensors.com by clicking “LOG IN” found in the top right corner.
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    and then enter your profile credentials
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    2. Select “SETTINGS” in the top right corner
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    3. Select the appropriate device group (found on the top middle of your screen) from the drop-down menu related to the sensors you are interested in sharing access to. You should see a list of devices found in the device group selected, check all devices that you plan to share access to.
    Screen Shot 2024-01-18 at 1.37.43 PM.png Screen Shot 2024-01-18 at 1.39.11 PM.png
    4. Once all devices are selected, click the “PERMISSIONS” button
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    5. Enter the email address of those you would like to share access with. Keep in mind, that they must have a username and password created prior to sharing access. Otherwise, an error stating that the account doesn’t exist will appear.
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    Let us know if you run into any issues! (support@tellusensors.com)
  1. Make sure you are logged in to your account. If you are not logged in, you will not be able to see your device. 
  2. Make sure you have the device selected (select the checkbox next to the device ID).


If you are still seeing an issue, please reach out to us at support@tellusensors.com and we’ll get back to you as soon as possible!

The humidity sensor found inside the AirU+ measures the relative humidity inside the device enclosure. This is helpful to understand device health and potential issues with the performance of the electronics. The humidity reading will effected by the elevated temperature of the device itself. As the temperature of the device increases, the humidity reading from the sensor is expected to decrease.

The AirU family of air quality monitors are equipped with sensors to monitor various air quality metrics, including temperature and humidity, which are crucial indicators for assessing the risk of mold growth. Mold tends to thrive in environments with high humidity levels (typically above 60%) and certain temperature ranges. By continuously monitoring temperature and humidity, your AirU provides insights into the environmental conditions that could promote mold growth.

While your AirU does not directly detect mold spores, its PM1/PM2.5 sensor and optional PM10 sensor can indirectly detect particles in the air that could indicate the presence of mold. Mold spores range in size from 1 to 100 micrometers, falling within the detection range of the PM1/PM2.5 and PM10 sensors. When mold spores become airborne, they can be captured by the PM sensors, alerting users to potential indoor air quality issues.

It’s important to note that while the PM1/PM2.5 and PM10 sensors can detect particles associated with mold, further testing may be required to confirm the presence of mold in a specific environment. Additionally, your AirU provides real-time data on temperature and humidity levels, allowing users to take proactive measures to prevent mold growth before it becomes a significant issue.

In summary, while your AirU can’t directly detect mold, it provides valuable data on temperature, humidity, and airborne particles that can help users assess the risk of mold growth and take appropriate actions to maintain healthy indoor air quality


The sensor is connected using similar steps as other popular smart devices like doorbell cameras, thermostats, and smart lights.

The AirU works 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

Setting up a crowd-sourced, air quality measurement network can be challenging. The sensors themselves are relatively inexpensive, but installing, maintaining, and ensuring equitable distribution of the sensor nodes requires effort. For example, crowd-sourced sensor networks that rely on community members to purchase and install their own sensors leads to few sensors being located in under-resourced (and often poorer air quality) areas.

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.  

AirView™ Map & Dashboard

AirView™, found on the home and dashboard pages, features icons representing public sensors, namely, AirU’s and PurpleAir sensors. These icons are color-coded to reflect their PM2.5 readings on the US EPA Air Quality Index scale from the past 15 to 30 minutes. If a sensor is shown in grey, it means it hasn’t provided a PM2.5 value in the last 15-30 minutes.

The air quality data starts transmitting within the first 5 minutes. However, the GPS location can take up to an hour to be reflected on the map.

The AirView Dashboard receives data through the TELLUS API from our TELLUS Cloud server. We retain all data indefinitely. To access historical data, you can simply specify your preferred date range. The device’s SD card stores a copy of all metrics for its entire lifespan. This SD card can be used as a fail-safe backup, and soon, a backloading feature will be available within 30 days to upload data from the SD card, filling gaps caused by Wi-Fi signal drops.

Absolutely! We encourage you to reach out to us for a demo. Our team is here to provide you with a firsthand experience of our products and answer any questions you may have. Don’t hesitate to get in touch, and we’ll be delighted to arrange a demo tailored to your needs and interests.


Colormap overlays serve as a sophisticated representation of real-time PM2.5 measurements within specific regions. These visualizations are particularly valuable in areas where we possess a sufficient network of sensors, enabling us to extrapolate and project air quality data to nearby areas. By leveraging this data modeling approach, we can provide a comprehensive and informative view of air quality conditions, even in locations where sensor coverage may be limited.

Our map overlays, a feature dedicated to providing insightful air quality information, are exclusively accessible in regions where we maintain an ample deployment of sensors. This requirement is imperative to ensure the accuracy and reliability of the data represented on these overlays. When we have a robust network of sensors in a given area, we can confidently generate these overlays, offering users a detailed and trustworthy perspective of air quality conditions in that specific location.

The data will be made available to you through our AirView platform. There, you will have access to dial gauges and time-series graphs for analysis and interpretation. You will also have access to the data through the AirView phone app. 

No, the information from the sensor will be integrated into our CoreDI models automatically. Users don’t need to do anything additional after connecting the sensor to their home Wi-Fi network.

You have the option to mark your sensor as private/public and indoor/outdoor. The Outdoor Public option is the only one that will show the location of the sensor. Choosing Private Outdoor will hide your location while still contributing to our CoreDI models. Selecting Indoor will omit your data from our models and keep your sensor location hidden.

If you’re unable to see your sensors on the dashboard, it might be due to the drawer being hidden in the optimized view. Here’s what you can do:

Open the Drawer: The drawer might be collapsed or hidden to optimize screen space. Look for a small icon or button typically located at the left of the screen. Tap on this arrow icon to expand or open the drawer.

If your issue persists even after opening the drawer or if it’s unrelated, please don’t hesitate to reach out to us at support@tellusensors.com. Our dedicated support team is here to assist you.

Data Access

When using the API, you will need to do some programming to interact with it effectively. However, to assist you in this process, we have a dedicated resource with examples and documentation available. You can access these valuable resources at the following link: API Documentation and Examples. This documentation includes helpful examples to guide you in utilizing the API to its fullest potential.

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

In the data studio, the timezone is local.

On your AirView™ dashboard, select the device you’re going to change. Click the edit button, and change to the desired name. (see images below for example)



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.

Calibration is an automated process that takes place in the background without requiring any user intervention.

In regions where we’ve already conducted modeling, we implement seasonal calibration factors to accommodate changing pollution patterns every quarter. Our goal is to have the entire United States comprehensively modeled within the next six months.

To check the areas where we’ve completed modeling, you can visit our website at https://airview.tellusensors.com/ and explore pollution heatmaps in various regions like Los Angeles, Lake Tahoe, Salt Lake City, Denver, Houston, Kansas City, St. Louis, Cleveland, Chattanooga, Springfield, MA, Boston, and more.”


Yes. Just complete the RMA form using this link and ship to the following address:

TELLUS Returns Dept – 2319 S. Foothill Drive – Suite 140 – Salt Lake City – UT – 84109