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

Measurements of hydroperoxides help improve our understanding of atmospheric oxidation processes. Here, we introduce an instrument setup designed for airborne hydroperoxide measurements. The HYdrogen Peroxide and Higher Organic Peroxides (HYPHOP) monitor has been deployed on the German High-Altitude and Long-range Observatory (HALO) aircraft and is based on dual-enzyme fluorescence spectroscopy, enabling measurements up to an ambient pressure of approximately 150 hPa pressure altitude (13.5–14 km). We characterized the measurement method and data acquisition of HYPHOP with special emphasis on potential sources of interference impacting instrument uncertainty. Physically derived interference was 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 instrument stability and potential parameters that might affect the measurements. We show that technical and physical challenges during flight maneuvers do not critically impact the instrument 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 and 19 pptv for a data acquisition frequency of 1 Hz. The determined instrumental temporal resolution is given at approximately 120 s.