Study of the uncertainty in NO2 chemiluminescence measurements due to the NO–O3 reaction in sampling lines

Abstract

Introduction The change in light intensity that takes place when an ambient air sample is drawn into the detection chamber of a chemiluminescence monitor generates changes in the concentrations of several species, such as NO2, NO and O3. Although this phenomenon has been known for several decades, there is still no commonly accepted approach on when or how to correct for it in NO2 and O3 readings.

Discussion In this work, we have assessed the expanded uncertainty of two chemiluminescence NO x analysers commercially available according to EN 14211:2005, with the aim of establishing the maximum allowable standard uncertainty due to the reaction between NO and O3 in the sampling system.

Conclusion Although this maximum allowable uncertainty cannot be a universal value—as it will depend on the performance of each analyser—our results have led us to propose the conservative value of 2%. We have also proposed a methodology for improving data quality which could be easily implemented by those responsible for air quality data validation.