Reply on RC2

Abstract. High-altitude aerosol research is crucial but faces significant cost and logistical hurdles that limit our ability to capture the highly variable vertical distribution of atmospheric trace substances. This paper introduces the Light-weight Observatory for sOuNdIng clouds and aerosol (LOONIS), a versatile, cost-effective, balloon-borne platform that provides an approach to address these challenges. LOONIS integrates a suite of lightweight instruments, such as optical particle counters, which provides real-time in situ detection of aerosol particle number and their microphysical properties, and impactors for collecting particles due to their inertia for subsequent offline physico-chemical analyses. Deployed during two measurement campaigns in Germany during August 2023 and June 2024, LOONIS provided insights into vertical aerosol distribution, capturing aerosol activation processes within saturated atmospheric layers. The platform demonstrated enhanced accuracy of particle concentration data from the UCASS instrument through the integration of a Thermal Flow Sensor (TFS). The deployment and resulting dataset underscore LOONIS’s capability as a tool for improving our understanding of atmospheric processes and potentially reducing the knowledge gap in atmospheric aerosol processes.