Elucidating the age and mixing state of summertime African dust transported across the tropical Atlantic Marine Boundary Layer
EMSL Project ID
61072
Abstract
Every summer, African dust is transported across the North Atlantic Basin causing widespread impacts on aerosol-radiation and aerosol-cloud interactions in addition to depositing critical nutrients to the ocean and Amazon Rainforest. These impacts critically depend on the mixing state of the dust, specifically, whether the dust has reacted with acidic gases or undergone cloud processing that can alter the hygroscopic properties and nutrient solubility of minerals found within the dust. Despite decades of research on African dust, we lack concrete information regarding whether dust is chemically aged after undergoing long-range transport. Single-particle measurements are needed to address this important research question but are lacking in this region. Without knowledge of dust mixing state, global climate models cannot accurately predict the radiative properties of dust transported across the N Atlantic marine boundary layer nor its impact on biogeochemical cycles. To address this gap, we propose to perform microscopy to analyze atmospheric particles (collected on filters and microscopy grids) to determine dust aerosol mixing state. This data will be used to determine chemical associations of aging markers, sea spray, and organic material with dust that alter its hygroscopicity and solubility upon deposition to the surface ocean. We will use samples collected at our site at Ragged Point, Barbados—a site in the eastern Caribbean Basin that has been used for over 50 years to document the long-range transport of African dust. We will also analyze samples collected on aircraft at the same time. We will focus on a one-week period during a major African dust transport event in August 2023. Preliminary analysis of a handful of these samples suggest that dust is externally mixed above cloud and mixed with marine emissions below cloud. However, analysis of more of these samples is urgently needed to complete and publish this dataset as well as generate enough preliminary results to apply for a large-scale proposal. From our preliminary results, we hypothesize that dust exhibits gradients in mixing state with increasing markers of “aging” with decreasing altitude that will impact the altitudinal extent of cloudiness as well as aerosol radiative properties with height. Computer-controlled scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (CCSEM/EDX) will be used to determine the size, source, and mixing state, including the association of dust with markers indicative of sea spray and chemical aging, of individual particles in our samples. The use of state-of-the-art EMSL instrumentation is critical for testing our hypothesis and for the overall success of this project. The CCSEM/EDX needed to distinguish dust aerosol mixing state is only possible through a collaboration with EMSL. This work will improve our understanding of whether dust aging occurs during transport and will motivate a large-scale proposal linking the dust aerosol mixing state with its relevant radiative properties. This proposal also aligns with DOE’s interest in aerosol aging, the physical, chemical, and optical properties of aerosols and the impact of dust on biogeochemical cycles that impact ecosystem health and Earth’s climate.
Project Details
Project type
Limited Scope
Start Date
2024-01-18
End Date
N/A
Status
Active
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members