Interactive comment on "Simultaneous measurement of δ 13 C, δ 18 O and δ 17 O of atmospheric CO 2 -Performance assessment of a dual-laser absorption spectrometer" by Pharahilda M. Steur et al. This is a good paper that deserves publication in AMT after revision. The authors did a great job in describing the mid-IR laser-based spectroscopic instrument for direct 17O-CO2 detection in air and reporting all relevant aspects of long-term operation and calibration of this instrument. The paper

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... s a lot of technical details and highquality data. However, underlying spectroscopic principles are only partially covered. This might be outside the main scope of the paper, but some brief explanations are desirable. The authors might consider addressing the following points: C1 AMTD Interactive comment Printer-friendly version Discussion paper