Dual-Source Transport, Vertical Evolution, and Topographic Modulation of the March 2023 East Asian Dust Storm in the Context of 2000–2024 Spring Dust Variability

East Asian spring dust activity has generally weakened since the early 2000s, but severe dust events continue to occur when synoptic forcing, source-region dryness, and terrain-guided transport are favorably coupled. This study places the 19-23 March 2023 East Asian dust storm within a 2000-2024 spring dust background and examines its horizontal transport, vertical evolution, source-receptor relationships, and topographic modulation. Long-term diagnostics based on MERRA-2 dust column mass concentration (DUCMASS), MAIAC aerosol optical depth (AOD), ERA5 meteorological fields, and land-surface variables show a broad decrease in spring dust loading, with a domain-mean Theil-Sen trend of -1.07 x 10^-6 yr^-1 and significant Mann-Kendall pixels covering 61.87% of the analysis domain. Against this declining background, the March 2023 event developed as a dual-source relay-convergence process. Taklamakan Desert dust was emitted first on 19 March and was transported southeastward along the Hexi Corridor, whereas Mongolian Plateau dust intensified on 21 March and mainly affected North China. TROPOMI absorbing aerosol index (AAI), CALIPSO vertical profiles, ground PM10 observations, CAMS EAC4 dust fields, ERA5 synoptic diagnostics, and FLEXPART-WRF forward and backward simulations jointly indicate that multi-level cold-vortex/trough-frontal coupling and terrain blocking controlled the event. The results show that extreme dust episodes can still occur under a weakening long-term dust background when dynamic lifting, dual-source activation, and topographic channeling act together.