Sensitivity of an infrared gas analyzer used in the differential mode, to partial gas pressures of carbon dioxide and water vapor in the bulk air

Abstract

An improved procedure for the preparation of calibration gases was used to determine the electrical output per unit specific gas pressure (the sensitivity) of carbon dioxide and water vapor infrared gas analyzers (IRGA) used in the differential mode. The IRGA instruments' sensitivity to differential carbon dioxide pressure decreased linearly as the partial carbon dioxide pressure increased. The analog linear decrease in sensitivity was also shown for a water vapor IRGA used in the differential mode. p] Near plant communities there is a djurnal variation in partial carbon dioxide and water vapor pressures which often reaches 20P and 1kP, respectively. Increases of 1P in partial carbon dioxide pressure and of 1 kP in partial water vapor pressure, reduce the IRGA sensitivity by 1 and 19%, respectively. p] If these temporal changes in IRGA sensitivity are ignored, an error of up to 20% in the estimation of carbon dioxide and water vapor gradients above plant communities can be encountered. A procedure is suggested for correcting measurements of water vapor and carbon dioxide gradients for such errors.