Altitudinal Gradient in Aging and Mixing State of Transported Saharan Dust in the Tropical North Atlantic Marine Boundary Layer: Insights from the MAGPIE Campaign

SUJAN SHRESTHA, Hope Elliott, Nurun Nahar Lata, Zezhen Cheng, Swarup China, Edmund Blades, Devon Blades, Alyson Allen, Rebecca Chewitt-Lucas, Jesus Ruiz-Plancarte, Albert Ortiz, Thomas Eck, Pawan Gupta, Elena Lind, Willem Marais, Robert Holz, Jeffrey Reid, Andrew Ault, Cassandra Gaston, University of Miami

     Abstract Number: 424
     Working Group: Coast to Coast Campaigns on Aerosols, Clouds, Chemistry, and Air Quality

Abstract
During the summer seasons, prevailing synoptic conditions facilitate the transport of Saharan dust across the Atlantic Ocean towards North America and the Caribbean, influencing biogeochemical cycles, climatic phenomena, and human health in important but poorly understood ways. Therefore, we present comprehensive aerosol physical and chemical measurements collected during the summer in 2023 at the University of Miami’s Barbados Atmospheric Chemistry Observatory (BACO) during the Moisture and Aerosol Gradients/ Physics of Inversion Evolution (MAGPIE) campaign. In addition to in-situ measurements and bulk chemical characterization, aerosol samples were collected at ground-level and both above and below cloud base aboard the NOAA Twin Otter aircraft for single-particle analysis. These samples were analyzed using computer controlled-scanning electron microscopy/energy dispersive X-ray spectroscopy (CCSEM/EDX) to elucidate chemical mixing state, particle size, and sphericity. During the campaign, days preceding and following Saharan dust events were primarily influenced by sea spray particles followed by internally mixed dust and sea spray particles. Whereas, during the peak dust event day, characterized by elevated aerosol optical depth (AOD) of ~0.8 and dust mass concentration of ~120 µg/m3, the aerosol composition showed a significant fraction of externally mixed mineral dust followed by internally mixed dust and sea spray particles. Notably, a substantial fraction of submicron biomass burning, and organic aerosols were co-transported alongside the dust. Assessment of the vertical gradient of aerosol measurements revealed altitudinal gradients in size, aging and mixing state of Saharan dust and these results can be used to improve uncertainties in current climate models regarding dust’s role on radiative effects and cloud processing in the tropical North Atlantic.