HYPHOP: a tool for high-altitude, long-range monitoring of hydrogen peroxide and higher organic peroxides in the atmosphere

Abstract. Measurements of hydroperoxides help improve the understanding of atmospheric oxidation processes. We introduce an instrumental setup designed for airborne hydroperoxide measurements. The instrument has been deployed on the German High-Altitude and Long-range Observatory (HALO) aircraft. The HYdrogen Peroxide and Higher Organic Peroxides (HYPHOP) monitor based on dual-enzyme fluorescence spectroscopy enables measurements up to ambient pressure of approximately 150 hPa pressure altitude (13.5–14 km). The main goal of this work is the characterization of the measurement method and data acquisition with special emphasis on potential interferences impacting instrumental uncertainty. Physically driven interferences were examined based on a dedicated test flight to investigate potential measurement inconsistencies arising from the dynamic movement patterns of the aircraft. During the test flight, the hydroperoxide monitor was operated in the background air sampling mode with purified air by scrubbing atmospheric trace gases, to investigate the instrumental stability and potential parameters that might affect the measurements. We show that technical and physical challenges during flight maneuvers do not critically impact the instrumental performance and the absolute measurements of hydroperoxide levels. Dynamic processes such as convective transport in the South Atlantic Convergence Zone (SACZ) are well-resolved as shown in the overview of a recent measurement campaign, Chemistry of the Atmosphere Field Experiment in Brazil in December 2022–January 2023 (CAFE-Brazil). The instrument precision based on the measurement results during CAFE-Brazil for hydrogen peroxide and the sum of organic hydroperoxides is estimated to be 6.4 % (at 5.7 ppbv) and 3.6 % (at 5.8 ppbv), respectively, and the corresponding detection limits 20 pptv and 19 pptv for a data acquisition frequency of 1 Hz, subsequently integrated over 120 second time intervals.