A drone-based rotating cascade impactor for single-particle analysis: Advancing aerosol mixing state research

Abstract

A novel drone-based aerosol sampling system, integrated with a rotating cascade impactor, was developed to enable size-selective sampling of atmospheric particles at upper altitudes. The system features rotating impaction stages that enable particle deposition suitable for single-particle analysis. For the first time, this platform was combined with Raman microspectroscopy (RMS) and surface-enhanced Raman spectroscopy (SERS) to perform detailed physicochemical characterization of airborne particles, including submicron aerosols, across ground level and aloft. Applied during a high-pollution event, the methodology enabled the characterization of particle mixing states, chemical functional groups, and size-dependent features that may be associated with aerosol transformation mechanisms. Single-particle analysis showed that internally mixed particles in the coarse-mode size range (1.35–5.5 μm) accounted for 53 % of the total in the upper-level sample, exceeding single-component particles by 20 %, which suggests multiphase processing and aging. Among sulfate-containing coarse particles, CaSO4 was the dominant species (38 %), indicating secondary formation through heterogeneous reactions during long-range transport In the submicron range (<1 μm), nitrate particles dominated (77 %), attributed to freshly formed aerosols resulting from coastal air masses with limited aging. These results highlight the significance of integrating high-resolution vertical aerosol profiling into atmospheric observations, revealing differences not captured by ground-based measurements. Beyond the field findings, this study also demonstrates the utility of a lightweight, drone-mounted rotating cascade impactor system, which enables scalable, size-selective, and altitude-resolved single-particle sampling under atmospheric conditions. This integrated approach offers a novel and practical framework for advancing both aerosol instrumentation and our understanding of atmospheric particle dynamics. © 2024