Integration and calibration of non-dispersive infrared (NDIR) CO₂ low-cost sensors and their operation in a sensor network covering Switzerland

• Main Authors: M. Müller, P. Graf, J. Meyer, A. Pentina, D. Brunner, F. Perez-Cruz, C. Hüglin, L. Emmenegger
• Format: Article
• Language: English
• Published: Copernicus Publications 2020-07-01
• Series: Atmospheric Measurement Techniques
• Online Access: https://www.atmos-meas-tech.net/13/3815/2020/amt-13-3815-2020.pdf

<p>More than 300 non-dispersive infrared (NDIR) <span class="inline-formula">CO₂</span> low-cost sensors labelled as LP8 were integrated into sensor units and evaluated for the purpose of long-term operation in the Carbosense <span class="inline-formula">CO₂</span> sensor network in Switzerland. Prior to deployment, all sensors were calibrated in a pressure and climate chamber and in ambient conditions co-located with a reference instrument. To investigate their long-term performance and to test different data processing strategies, 18 sensors were deployed at five locations equipped with a reference instrument after calibration. Their accuracy during 19 to 25 months deployment was between 8 and 12&thinsp;ppm. This level of accuracy requires careful sensor calibration prior to deployment, continuous monitoring of the sensors, efficient data filtering, and a procedure to correct drifts and jumps in the sensor signal during operation. High relative humidity (&gt;&thinsp;<span class="inline-formula">∼85 <i>%</i></span>) impairs the LP8 measurements, and corresponding data filtering results in a significant loss during humid conditions. The LP8 sensors are not suitable for the detection of small regional gradients and long-term trends. However, with careful data processing, the sensors are able to resolve <span class="inline-formula">CO₂</span> changes and differences with a magnitude larger than about 30&thinsp;ppm. Thereby, the sensor can resolve the site-specific <span class="inline-formula">CO₂</span> signal at most locations in Switzerland. A low-power network (LPN) using LoRaWAN allowed for reliable data transmission with low energy consumption and proved to be a key element of the Carbosense low-cost sensor network.</p>