Q: How does my Airthings product measure VOCs?
A: Airthings uses a metal-oxide based sensor with a sensitive layer that reacts to chemicals by adsorption. This type of sensor will react to most volatile organic compounds, with some exceptions (like CO2), but is not able to differentiate between them. Its sensitivity depends on the compound, which means it will give a larger signal for some chemicals than others, even though the concentration is the same. It is a relative sensor that adapts to its environment over time.
Q: What does it mean that the VOC sensor is a “relative sensor”?
A: Like our nose, the sensor will eventually get used to the environment it is in. The sensor measures the amount of VOCs relative to the cleanest air it has seen the last week or so. This means that it must see clean, fresh air at regular intervals to be able to detect VOCs properly. If it is sitting in an environment with constantly high levels over time, it will eventually (after a week or so) be tricked into reporting the air as clean.
Q: How accurate is the VOC sensor?
A: Unlike our other sensors, Airthings does not provide data on accuracy for the VOC sensor. The sensor response depends on the mix of compounds in the air, and its output is scaled to give the most correct reading for one common mix of compounds (the VOCs that are in our breath). But if the mix of VOCs it sees is different than this, its output might be significantly off. This is even true for professional VOC reference monitors, that only provide an accurate reading if the mix of compounds is known and adjusted for. The sensor output should only be used as guidance, and the levels not relied upon for health critical decisions, and should not be used to detect specific gases.