Abstract. At the end of 2015, a CO2/CH4/CO Cavity Ring-Down Spectrometer (CRDS) was installed at the Izaña Global Atmosphere Watch station (Tenerife, Spain) to improve the Izaña Greenhouse gases GAW measurement programme, and to guarantee the renewal of the instrumentation and the long-term maintenance of this programme. We present the results of the CRDS acceptance tests, the processing of raw data applied through novel numerical codes, and the response functions used. Also, the calibration results, the implemented water vapour correction, the target gas injection statistics, the ambient measurements performed from December 2015 to July 2017, and their comparison with other continuous in situ measurements are described. The agreement with other in situ continuous measurements is good most of the time for CO2 and CH4, but for CO is just outside the GAW 2-ppb objective. It seems the disagreement is not produced by significant drifts in the CRDS CO WMO tertiary standards. The main novelties are: 1) determination of a slight CO2 correction that takes into account changes in the inlet pressure/flow rate; 2) detailed justification of the use of virtual tanks to monitor the response function changes in time; 3) drift rate determination for the pressure and temperature sensors located inside the CRDS cavity; 4) novelties in the determination of the H2O correction for CO; and 5) determination and discussion of the origin of the CRDS-flow inlet pressure and H2O dependences.
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