CORA - a dedicated device for carbon dioxide monitoring in cave environments

Abstract

High resolution time-series of cave CO 2 fluctuations are increasingly demanded to quantify calcite precipitation processes. CORA, an energy-efficient NDIR-device, has been specifically developed for the long-term monitoring of carbon dioxide in remote cave environments. To allow comparison between different cave sites, changes in air pressure and temperature are compensated for using dedicated probes. Laboratory experiments demonstrate that CORA's precision is adapted to the analysis of spatially and temporally variable CO 2 regimes and therefore suitable for a large number of applications. Data obtained with 12 independently calibrated instruments are reproducible within 3% (1σ). The two-point calibration function is validated using certified reference gases for an overall accuracy determined at ±50 ppmv, resp. ≤±3%. Although no significant drift was observed during the test phase a periodic recalibration is recommended. Initial results from field studies show that continuous monitoring over a full annual cycle is possible at 4 hour intervals without specific maintenance.