Measurements of the size distribution of atmospheric aerosols and cloud particles are fundamental not only for understanding the physical processes that govern aerosol-cloud interactions but also to gain statistical insight into the microphysical properties. Measuring the aerosol content of a local environment plays a key role in modern environmental and occupational health monitoring. Optical Particle Counters (OPCs) are a common instrument used to measure the aerosol particle concentration and size distribution. The Universal Cloud and Aerosol Sounding System (UCASS) is a novel balloon-borne open-path optical particle counter that has been developed at the University of Hertfordshire. In spring 2017, UCASS measurements of mineral dust particles have been performed during campaigns at the eastern Mediterranean (Cyprus and Greece) – a region strongly affected by dust storms from western Africa to central Asia. In order to assess the quality of the aerosol size distributions obtained from UCASS soundings, UCASS findings will be compared to coinciding independent measurements with research aircraft as well as to the ones retrieved by combining data from sun photometer and lidar. This data will be used to evaluate the performance of UCASS within different aerosol layers and to assess whether UCASS could be used as an affordable alternative to research aircraft for in-situ profiling of the size distribution of mineral dust particles. If UCASS data is found as reliable and representative, it will provide a new option to obtain aerosol data that can be used for the validation of in-situ and remote sensing instrumentation, as well as global aerosol models.