Abstract
African mineral dust is transported many thousands of kilometres from its source regions and, because of its ability to nucleate ice, it plays a major role in cloud glaciation around the globe. The ice-nucleating activity of desert dust is influenced by its mineralogy, which varies substantially between source regions and across particle sizes. However, in models it is often assumed that the activity (expressed as active sites per unit surface area as a function of temperature) of atmospheric mineral dust is the same everywhere on the globe. Here, we find that the ice-nucleating activity of African desert dust sampled in the summertime marine boundary layer of Barbados (July and August, 2017) is substantially lower than parameterizations based on soil from specific locations in the Saharan desert or dust sedimented from dust storms. We conclude that the activity of dust in Barbados’ boundary layer is primarily defined by the low K-feldspar content of the dust, which is around 1 %. We propose that the dust we sampled in the Caribbean was from a region in West Africa (in and around the Sahel in Mauritania and Mali), which has a much lower feldspar content than other African sources across the Sahara and Sahel.
Highlights
The formation and growth of ice crystals strongly affects the properties of clouds and has important implications for cloudclimate feedbacks [Storelvmo, 2017]
Our results show that transported mineral dust in the Caribbean marine boundary layer (MBL) has a relatively low activity compared to dust samples in the African sources, parameterisations based on the icenucleating activity of surface samples from those sources will produce ice-nucleating particles (INPs) concentrations that are too high
The activity of African dust in Barbados, in terms of active sites per unit surface area, is several orders of magnitude lower than parameterisations based on dusts sampled from the surface in Africa that were later analysed in a laboratory
Summary
The formation and growth of ice crystals strongly affects the properties of clouds and has important implications for cloudclimate feedbacks [Storelvmo, 2017]. Mineral dusts generated from desert soils are composed of various minerals, with the three most abundant groups in the atmosphere being clay, quartz and feldspar [Murray et al, 2012; Perlwitz et al, 2015] These dusts are created by the physical and chemical weathering of the Earth’s surface and are commonly sourced from arid regions in Africa, the Middle East and 55 Asia [Prospero et al, 2002a]. Maring et al 115 [2003a] point out that wet scavenging was a minor loss route, since the small cumulus clouds which form in dusty air do not regularly precipitate These small cumulus clouds are not supercooled and INPs are not preferentially scavenged through growth and precipitation of ice. The size distribution of African dust is remarkably stable across the Atlantic. It is clear that the properties of dust in the Caribbean MBL may be distinct from those in 125 the SAL since the sources and transport pathways are distinct
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
