A measurement system is disclosed that includes features for detecting the presence of nitric oxide from a gas sample, such as exhaled breath. The measurement system includes an assembly that introduces one or more reducing gases into a reactor-sensor assembly to help stabilize the sensor signal response and improve the performance of the assembly over time. Suitable reducing gases include hydrogen gas (H 2 ), carbon dioxide (CO), benzaldehyde, bisphenol A, and other similar compounds. The reducing gas may be introduced directly from one or more surrounding gases or through tubing or inline piping. The reducing gas may be generated from the liquid or solid forms.