Mineral Dust Aerosol Measurements throughout the Global Free Troposphere

Mineral dust aerosol particles impact the Earth's radiative balance via direct scattering and absorption of light and by promoting ice cloud formation. Modelling studies suggest that mineral dust is a leading contributor to aerosol optical depth throughout much of the globe. Lab and field studies indicate that dust particles are efficient ice nuclei, and recent airborne measurements confirm the dominant role of mineral dust on cirrus cloud formation in the Northern Hemisphere. However, the net climate impact of mineral dust is not well constrained in part due to the absence of dust abundance measurements above the Earth's surface. We present new airborne mineral dust measurements from the 2016-2017 NASA ATom (Atmospheric Tomography) campaigns that cover the entire Pacific and Atlantic basins from the boundary layer through the free troposphere. This global dataset fills a critical measurement gap for dust concentrations in the background atmosphere. We highlight vertical distributions, hemispheric gradients, and dust's role in cirrus formation. Measured dust concentrations were compared to a global simulation using a sectional aerosol scheme. Although large emission sources such as the Sahara were well described, model-measurement discrepancies were greatest at cirrus altitudes. We investigate these discrepancies though sensitivity studies of dust emission, removal, and vertical transport.