Calibration of a gas sensor

A method of calibrating a gas sensor comprising a luminescent compound having a luminescence lifetime that is quenched by a gaseous substance which uses a model of the relationship between the luminescence lifetime and the concentration of the gaseous substance that is modified by a calibration factor representing a proportion of the compound not being exposed to the gaseous substance, the method comprising:

• measuring values of the luminescence lifetime of the luminescent compound while the gas sensor is exposed to at least two known concentrations of the gaseous substance;
• and
• deriving the calibration factor from the measured values of the luminescence lifetime using the model.

A gas sensor apparatus for measuring the concentration of a gaseous substance in an environment, the gas sensor apparatus comprising:

• a gas sensor comprising a luminescent compound having a luminescence lifetime that is quenched by the gaseous substance, and a detector configured to detect light emitted by the luminescent compound;
• and
• an analysis system configured to derive a luminescence lifetime of the compound from the signal output by the detector, and to derive a concentration of the gaseous substance from the measured luminescence lifetime using a model of the relationship between the luminescence lifetime and the concentration of the gaseous substance that is modified by a calibration factor representing a proportion of the luminescent compound not being exposed to the gaseous substance.