The challenges facing low cost air quality sensors
Rise of the low-cost sensor
Air pollution is a hot topic in the recent years. A growing number of people care about the surrounding air quality. Normally, reliable air quality data can only be obtained from the Environmental Protection Department (EPD), which measure air quality using traditional air monitoring instruments.
It is a challenge for government(s) to service the rising public demand for air quality information. Traditional air monitoring stations generally use optical instruments that offer precise and accurate air quality data, but at a high cost. Due to this limitation, dozens of devices/instruments for air quality measurement made of low-cost sensors have popped up in the market.
Low-cost sensors react to the target pollutants/gases via chemical reaction (electrochemical), optical absorption (NDIR), light scattering or absorption (optical particle counter) and so on. They are portable, low-cost & highly customized.
But they face some key challenges.
Ambient interference & Calibration
Firstly, they are highly affected by the ambient environmental factors (e.g. Most PM sensor may fluctuate with the relative humidity, and may output “crazy” values while raining). Also, some of the low-cost sensors will not only react to one pollutant, in the other word, they are facing cross interference issue (e.g. nitrogen dioxide sensor is normally showing the reaction with ozone and/or other nitrogen oxides). So:
• If you directly purchase the sensors and DIY your own device: The manufacturer may offer the initial converting factors, which is most likely obtained under a stable laboratory environment. That means you will probably get completely wrong measurement values (even negative) if only using the manufacturer parameters.
• If you spend more money, and purchase the ready-to-go device: The seller may (or may not) solve the calibration issue we mentioned above with several traditional expensive reference air quality monitoring instruments. You are getting a “black-box” device and have to determine whether to trust the measurement values you get.
A bunch of researches/projects could be found online which are utilizing these sensors without mentioning the data quality.
Aging & Drift
Secondly, as we know, almost all electronic devices are encountering the aging issue. The low-cost sensors are certainly among this group. People should realize that these sensors are “low-cost” as a kind of consumables. For example, a high quality (with a higher price) electrochemical sensor cell could last for two years with 80 percent decayed outputs. Hence, a drift of the measurement values will raise at a time point.
Regulation & Trust
Finally, a key problem is that there is no regulation for the low-cost sensors/devices, which leads to the chaotic market. Undeniably, the low-cost sensors is a “gold mine” if they could be used correctly. Currently, researchers and manufacturers are putting a lots of effort into regulation.
What we do
We collaborate with Tracegas group, LMU, who are experts in air quality monitoring and assessment to tackle these challenges. Our algorithms are undergoing field trials in Munich with positive results. We want to enable a new era of air quality measurement.
- Sheng Ye, Research Scientist, Signify GmbH.