The Importance of Water Vapor Measurements and Corrections

Water vapor is known to influence the measurement of carbon dioxide by infrared gas analysis in several ways, which can lead to significant measurement errors. Spectral cross-sensitivity due to absorption band broadening, and inherent instrument cross sensitivity can both cause over estimations of CO2 mole fraction in samples containing water vapor when their effects are not accounted for. Dilution of samples by the addition of water vapor may not be important when measuring actual CO₂ mole fractions, but can lead to significant errors in flux measurements. This application note describes the basis of each of these three processes and discusses how each can affect the measurement of CO₂.