Good performance of low-cost carbon dioxide sensor based on intercomparisons with the standard eddy-covariance system

Abstract. Flux measurements have started to play an important role outside academia in assessing carbon sinks of different ecosystems and land-use types. If natural carbon solutions are to be deployed and monetized in carbon markets, more low-powered and low-cost flux systems should be deployed. There is a growing need for low-cost sensors that still fulfil the requirements for scientific applications. We present a case study where Vaisala company and the University of Helsinki joined their industrial and academic competencies to create an inexpensive yet precise fast-response carbon dioxide (CO₂) and water vapour (H₂O) sensor. A working prototype was developed and field-tested against a scientific reference eddy covariance (EC) setup. Special attention was paid to response time, lowered sampling frequency, and auto-calibration related to the temperature. The results at the end of the project were very promising. The enclosed-path EC prototype had a CO₂ response time of 0.18 sec and a noise level of 1 ppm at a 5 Hz sampling rate. The internal auto-calibration procedure was continuously improved such that CO₂ signal drifting was avoided and the instrument was capable of measuring CO₂ fluxes with high correlation relative to the reference EC setup (R² = 0.98).