Combined Measurements of Meteorological Variables, Atmospheric Electricity and Aerosol Particle Concentration using a Small Uncrewed Aircraft System

Abstract

The Uncrewed Aircraft System (UAS) Multipurpose Airborne Sensor Carrier, version 3 (MASC-3), which is capable of measuring the three-dimensional wind vector, air temperature, and humidity at high resolution, was used in this thesis as a starting point in the development of a system that can simultaneously measure meteorological variables, atmospheric electricity, and aerosol particle concentration and size distribution. The aim of this development was to be able to accurately record Saharan dust events and, in contrast to existing measurements, to make insitu measurements of all of the above variables simultaneously. This is important because no such combined measurements exist to date, and in particular, the influence of atmospheric electricity on aerosol particle transport is still largely unexplored. This thesis consists of three publications, each dealing with one aspect of this combined measurement system. First, MASC-3 was used to measure the local wind field in an Arctic fjord at high resolution. It was shown that the wind field in Kongsfjorden, in the immediate vicinity of the Ny-Alesund research station on ˚ Svalbard, is complex and strongly influenced by the local terrain. MASC-3 captured small-scale katabatic flows that affect aerosol particle transport in the immediate vicinity of the research station, which are not resolved in large-scale numerical models. Second, a sensor payload was developed for MASC-3 to measure the space charge in the atmospheric electric field. Validation measurements of this sensor system were performed by flying MASC-3 past a 100 m high metallic measurement mast. A simulation of the electric field around the mast was compared with the measurement data, and it was shown that MASC-3 was able to measure the changes in the electric field around the mast with low noise after the signal from the charge sensors was corrected to remove the influence of the aircraft motion. Finally, a low-cost Optical Particle Counter (OPC) was integrated into MASC-3 to measure aerosol particle concentration and size distribution. For this purpose, the OPC was equipped with a passive aspiration system and a diffusion dryer and integrated into an airfoil-shaped pod. The measurement system was validated both in ambient conditions against a reference instrument and in a wind tunnel. The three measurement methods were combined in the measurement of a Saharan dust event over Cyprus, where aerosol particle concentration, wind, temperature, humidity, and space charge were measured simultaneously. The resulting measurements can be used in the future to investigate fundamental relationships in aerosol particle transport.