UAV observations to reveal new insights into dust particle morphology and orientation

Atmospheric dust affects the Earth’s radiation budget through scattering and absorption, processes governed by its optical properties linked to their microphysical characteristics (size, shape, refractive index, and orientation). While knowledge of dust particle size has progressed in the last few decades, dust morphology remains poorly constrained beyond the generic category of “irregular particles”. Although some studies suggest that dust particles can exhibit preferred orientations within the atmospheric column, most radiative-transfer models still represent dust as ensembles of randomly oriented spheres or spheroids. The limited availability of direct observational evidence limits our understanding of how dust’s non-sphericity and orientation influence remote-sensing retrievals, atmospheric processes, and aerosol radiative forcing. Given that mineral dust accounts for one of the largest global mass fluxes of primary aerosols, reducing these uncertainties is crucial to better constrain its overall radiative impact.

 

To address these gaps, we collect new UAV-based datasets on dust particle shape, internal structure, and orientation. In spring 2025, the Cyprus Institute conducted a two-month UAV campaign aiming for two goals: (1) to advance airborne dust-sampling methods, and (2) to investigate dust composition, size, shape, and orientation. Multiple UAV platforms were deployed during eight dust-affected flight days, guided by daily dust and weather forecasts. This strategy enabled sampling of diverse atmospheric conditions, including a strong dust event on 17/05/2025 with total AOD at 500- nm approaching the value of 1. Additional campaigns will further expand the dataset.

 

The UAV payloads included the Compact Optical Backscatter Aerosol Detector (COBALD) and Giant Particle Collectors (GPAC), supplemented by Optical Particle Counters (OPCs). To detect signatures of particle orientation two COBALD instruments, each operating at two wavelengths (455 and 940 nm), were deployed in a dual-field-of-view configuration pointing horizontally and vertically with two nearly orthogonal viewing directions. GPAC were adapted to carry TEM grids (small, ultra-thin mesh substrates used to collect particles for transmission electron microscopy) enabling airborne dust sampling suitable for high-resolution imaging and 3-D reconstruction of particle morphology. These combined measurements provided a unique dataset for assessing dust particle morphology, size, and potential orientation effects in the atmospheric column.