Exploring Aerosol-Climate Interactions over the Benguela Upwelling Zone: A Multifaceted Analysis of DMS Emissions, Aerosol Composition, and Climate Implications

MASHIAT HOSSAIN, Hannah Horowitz, Rebecca Garland, University of Illinois at Urbana-Champaign

     Abstract Number: 607
     Working Group: Aerosol-Ecosystem Interactions

Abstract
The west coast of southern Africa features complex interactions among land, atmospheric, and oceanic components. The diverse aerosol composition along with persistent stratocumulus clouds contribute to significant uncertainties in aerosol radiative forcing and climate sensitivity. While previous research focused on biomass burning during the austral dry season due to its substantial regional aerosol load, it is imperative to examine ocean-atmosphere linkages to predict future climatic trends. Coastal upwelling in the Benguela region supports high phytoplankton production with seasonal blooms generating aerosol precursors such as dimethyl sulfide (DMS). This study explores the intricate relationships among phytoplankton activity, DMS emissions, and aerosol composition, considering seasonal variations for a holistic understanding of the system. Furthermore, the work primarily aims to elucidate the key chemical components, such as sulfate aerosols and sea-salt particles, which potentially contribute to aerosol-cloud interactions within the upwelling region. To achieve this, we employ the GEOS-Chem global three-dimensional chemical transport model within a high-resolution (~50 km) one-way nested grid over the SE Atlantic and Southern Africa. Analysis of the vertical aerosol composition over the ocean uncovers a higher sulfate mass in September compared to January, despite a higher percentage composition during January, which coincides with peak DMS emissions. Conversely, aerosol composition in September is predominantly characterized by total organic aerosols, likely from biomass burning. We perform sensitivity analyses to assess the uncertainty in aerosol composition due to DMS chemical mechanisms and marine primary organic aerosol emissions. Satellite-derived coccolithophore index is used to estimate the impact of uncertainty in DMS emissions. We evaluate modeled aerosols against aircraft campaigns and long-term monitoring stations. This research will contribute to advancements in the parameterization of ocean-atmosphere coupling, refining the representation of marine aerosols in atmospheric models linked to phytoplankton characteristics.