Revealing the evolution of aerosols in Asian dust events: Insights from their microphysical and elemental...

Dust particles and their complex interactions with anthropogenic pollutants have caused serious environmental pollution in East Asia. However, there are few observations on the real-time response to the morphological and mixing state changes of individual dust particles. We used a newly developed single-particle optical particle counter (SOPC) for real-time detection of single-particle size and the depolarization ratio (defined as the ratio of the vertical component to the parallel component of backward scattering), combined with an intelligent scanning electron microscope environmental-particle analysis system (IntelliSEM-EPAS), to quantitatively study the evolution process of particle morphology and chemical composition during dust events in March 2023. Fine mode particles dominated the total particle number concentration, with the proportion of sub-1 μm particles reaching 90.3 %. The depolarization ratio and form factor (single-particle morphology parameters automatically obtained via IntelliSEM-EPAS) of individual fine particles markedly changed (increased from 0.05 to 0.12 and decreased from 0.73 to 0.60, respectively) during the dust events. Further elemental analysis revealed that mixed sulfur-containing particles play a crucial role in the overall morphological changes in fine particles. During the large-scale transmission of dust aerosols, their morphology and mixing state undergo significant changes. Quantitative description of these changes is beneficial for better understanding the uncertainty of the evolution of dust events and model simulations.