Water vapour in natural gas can affect the safety of transmission of the gas in pipelines, and affects its price at custody transfer when pipeline gas is bought and sold. Water vapour must be removed to a regulated level. Therefore, accurate measurement of the humidity of the gas is important to ensure the gas meets pipeline specifications.
Hygrometers, including a variety of water-vapour spectrometers, are used to make these measurements and offer a fast response. However, some of these instruments can be sensitive to the composition of the natural gas, so gas-specific calibration is needed to avoid errors in measuring in these gases.