https://doi.org/10.5194/amt-2019-408 Preprint. Discussion started: 18 November 2019 c Author(s) 2019. CC BY 4.0 License. Integration and calibration of NDIR CO2 low-cost sensors, and their operation in a sensor network covering Switzerland Michael Mueller1, Peter Graf1, Jonas Meyer2, Anastasia Pentina3, Dominik Brunner1, Fernando Perez- Cruz3, Christoph Hüglin1, and Lukas Emmenegger1 5 1Empa, Swiss Federal Institute for Materials Science and Technology, Duebendorf, Switzerland 2Decentlab GmbH, Duebendorf, Switzerland 3Swiss Data Science Center, Zurich, Switzerland Correspondence: Michael Mueller (
[email protected]) Abstract. 10 More than 300 LP8 CO2 sensors were integrated into sensor units and evaluated for the purpose of long-term operation in the Carbosense CO2 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 to 12 ppm. This level of accuracy requires 15 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 (> ~85%) 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 CO2 changes and differences with a magnitude larger than about 20 ppm.