MoMuCAMS: A new modular platform for boundary layer aerosol and trace gas vertical measurements in extreme environments

Abstract

The Modular Multiplatform Compatible Air Measurement System (MoMuCAMS) is a newly developed in situ aerosol and trace gas measurement payload for lower atmospheric vertical profiling in extreme environments. MoMuCAMS is a multiplatform compatible system, primarily designed to be attached to a helikite, a rugged tethered balloon type that is suitable for operations in cold and windy conditions. The system addresses the need for detailed vertical observations of atmospheric composition in the boundary layer and lower free-troposphere, especially in polar and alpine regions. These regions are known to frequently experience strong temperature inversions, preventing vertical mixing of aerosols and trace gases, and therefore reducing the representativeness of ground-based measurements for the vertical column, causing a large informational gap. The MoMuCAMS encompasses a box that houses instrumentation, a board computer to stream data to the ground for inflight decisions, and a power distribution system. The enclosure has an internal volume of roughly 100 L and can accommodate various combinations of instruments within its 20 kg weight limit. This flexibility represents a unique feature, allowing the simultaneous study of multiple aerosol properties (number concentration, size distribution, cluster ions, optical properties, chemical composition and morphology), as well as trace gases (e.g. CO, CO2, O3, N2O) and meteorological variables (e.g., wind speed and direction, temperature, relative humidity, pressure) . To the authors’ knowledge, it is the first tethered balloon based system equipped with instrumentation providing a full size distribution for aerosol particles starting from 8 nm, which is vital to understanding atmospheric processes of aerosols and their climate impacts through interaction with direct radiation and clouds. MoMuCAMS has been deployed during two field campaigns in Swiss Alpine valleys in winter and fall 2021. It has been further deployed in Fairbanks, Alaska (USA) in January–February 2022, as part of the ALPACA (Alaskan Layered Pollution and Chemical Analysis) campaign and in Pallas, Finland, in September–October 2022, as part of the PaCE2022 (Pallas Cloud Experiment) study. The system flew successfully at temperatures of −36° C, in wind speeds above 15 m s−1 and in clouds. Here we present a full characterization of the specifically developed inlet system and novel, hitherto not yet characterized, instruments, most notably a miniaturized scanning electrical mobility spectrometer and a near-infrared carbon monoxide monitor. Three cases from one of the Swiss Alpine studies are presented to illustrate the capability of MoMuCAMS to perform high-resolution measurements with different instrumental setups. We show two case studies with surface-based inversions in the morning that allowed for observation of aerosol and trace gas dynamics in evolving boundary layer conditions. The vertical structure of the boundary layer featured in both cases a surface layer (SL) with a top between 50 and 70 m above ground level, dominated by traffic emissions leading to particle number concentrations up to seven times higher than in the residual layer above. Following sunrise, turbulent mixing led to rapid development of a mixed boundary layer and dilution of the SL within one to two hours. The third case study illustrates the capability of the system to perform aerosol sampling at a chosen altitude over several hours, long enough in low aerosol concentrations environments to perform chemical analyses. Trace elements were analyzed using inductively coupled plasma tandem mass spectrometry. The samples were also analyzed under a scanning electron microscope with energy dispersive x-ray and a transmission electron microscope to gain additional insights into their morphology and chemical composition. Such analyses are suitable to gain deeper insights into particles’ origins, and their physical and chemical transformation in the atmosphere. Overall, MoMuCAMS is an easily deployable tethered balloon payload with high flexibility, able to cope with the rough conditions of extreme environments. Compared to uncrewed aerial vehicles (drones) it allows to observe aerosol processes in detail over multiple hours providing insights on their vertical distribution and processes, e.g. in clouds, that were difficult to obtain beforehand.