New photolytic converter for improving aircraft measurements of NO₂ via chemiluminescence

Abstract. Nitrogen oxides (NOx ≡ NO + NO2) are centrally involved in the photochemical processes taking place in the earth’s atmosphere. Measurements of NO2, particularly in remote areas where concentrations are of the order of pptv, are still a challenge and subject to extensive research. In this study, we present NO2 measurements via photolysis-chemiluminescence during the research aircraft campaign CAFE Africa (Chemistry of the Atmosphere – Field Experiment in Africa) 2018 around Cabo Verde as well as the results of laboratory experiments to characterize the photolytic converter used. We identify a memory effect within the conventional photolytic converter associated with high NO concentrations and rapidly changing water vapor concentrations, accompanying changes in altitude during aircraft measurements, which is due to the porous structure of the converter material. We test and characterize an alternative photolytic converter made from quartz glass which improves the reliability of NO2 measurements in laboratory and field studies