High-resolution observation of aerosol particle size distribution and chemical evolution during two consecutive dust...

Dust events significantly impact air quality and atmospheric composition in downwind urban areas, but their dynamic mixing with anthropogenic pollutants remains inadequately characterized at high temporal resolution. This study investigated two consecutive dust events in Xi'an (Guanzhong Basin, Northwest China) during April 2025, using high-frequency observations (1-min resolution) of particle size distribution (0.30 to 9.43 µm), water-soluble inorganic ions, and meteorological parameters, combined with NOAA HYSPLIT backward trajectories. The first event exhibited a "two-step" evolution: initial boundary-layer compression drove accumulation of anthropogenic fine particles (0.30 to 0.57 µm) and secondary ions, followed by dilution by coarse-mode desert dust (> 0.80 µm) with elevated crustal ions. The second event showed a simplified "one-step" pattern dominated by synchronous increases in coarse/fine particles, with minimal anthropogenic influence due to prior atmospheric cleansing (dilution, transport, and removal of pollutants) by the first event. Backward trajectories confirmed transboundary transport from the Mongolian Plateau and Inner Mongolia. Size-resolved analysis revealed an inverse relationship between fine and coarse particles during the first event: fine particle number concentrations increased by > 500% in the early stage but declined to 10 to 20% of peak values after coarse dust arrival. These findings highlight the dual role of dust as both a pollution carrier and atmospheric cleanser, and underscore the importance of pre-event atmospheric conditions in shaping dust-pollutant mixing. This study provides high-resolution insights into dust evolution in basin terrain, supporting refined air quality forecasting for dust-affected urban areas.