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Calibration experiments were executed to document pertinent calibration methods for open-pathinfrared gas analyzer (OP-2) in field operations and to quantify their performance characteristics incontinuous long-term flux measurements. Based on our results, we concluded: (1) flow rate of 2.0 L min-1can be used for calibration instead of the recomended 0.5 L min-1. Such faster flow rate brings thesampled air in the calibration hood at equilibrium within 5 min for CO2 and 10 min for H2O; (2) afterreaching equilibrium, two-minute average sampling for related variables per each concentration maybe sufficient; (3) use of four concentration is needed to derive the nonlinear calibration equation forwater vapor with 1% uncertainty of flux measurement; and (4) the resultant calibration interval forOP-2 for both CO2 and H 2O is approximately one month.