FAQ

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.

The AirU Legacy Sensor is about 4” x 4” x 4”.

The AirU+ Sensor is about 4.7″ x 4.7″ x 2.4″.

The AirU+ PM10 Sensor is about 7.9″ x 4.7″ x 3.6″.

The AirU Pro Sensor is about 7.6″ x 5.3″ x 3.6″.

Visual Guide

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.