A study of systematic biases and measurement uncertainties in ozone mole fraction measurements with the NIST Standard Reference Photometer

Sources of bias in the National Institute of Standards and Technology ozone Standard Reference Photometer (SRP) maintained by the Bureau International des Poids et Mesures have been investigated. A relative bias of −0.4% in the ozone mole fraction measurement caused by a temperature gradient in the gas cells of the instrument was characterized and corrected for in a modified version of the instrument. A second relative bias of +0.5% due to the multiple reflections of light within the gas cells was also corrected. The Guide to the Expression of Uncertainty in Measurement approach was used to develop an uncertainty budget for the modified SRP, including a relative value for the ozone absorption cross-section uncertainty of 2.1% (k = 2). The measurement uncertainty for the bias-corrected SRPs is enlarged compared with earlier studies, but their comparability improved.