Differences and Similarities of Central Asian, African, and Arctic Dust Composition from a Single Particle Perspective

Abstract

Mineral dust composition affects a multitude of processes in the atmosphere and adjacent compartments. Dust dry deposition was collected near source in northwest Africa, in Central Asia, and on Svalbard and at three locations of the African outflow regime. Samples were subjected to automated scanning electron microscopy with energy-dispersive X-ray analysis to obtain size and composition of 216,000 individual particles. Results show low temporal variation in estimated optical properties for each location, but considerable differences between the African, Central Asian, and Arctic regimes. No significant difference was found between the K-feldspar relative abundances, indicating comparable related ice-nucleation abilities. The mixing state between calcium and iron compounds was different for near source and transport regimes, potentially in part due to size sorting effects. As a result, in certain situations (high acid availability, limited time) atmospheric processing of the dust is expected to lead to less increased iron solubility for near-source dusts (in particular for Central Asian ones) than for transported ones (in particular of Sahelian origin).Atmosphere 2020, 11, 269 2 of 16 Dust composition also affects the marine and terrestrial biosphere by supplying nutrients, but also supplying substances with adverse health effects [20]. Tropical as well as extra-tropical ecosystems apparently rely in part on atmospheric inputs [21,22]. Ocean surface waters can be depleted in essential nutrients supplied by the dust [23,24], thus composition plays an important role [25,26].Several of these effects are not only affected by the overall composition, but also by the distribution of the compounds between the particles (i.e., internal or external mixing). For example, optical properties are strongly dependent on the mixing state [27,28]. In addition, chemical processes might be considerably affected by the particle mixing state [29].Consequently, a more detailed knowledge of dust composition is expected to yield a better understanding and increased model quality. Information on bulk aerosol is available with respect to different properties (e.g., [6,7,30,31]) and finds its way into models [32]. In contrast, detailed properties like the aerosol mixing state are generally not yet regarded, probably due to scarcity of this information.In the present study, dust from different transport regimes-African near-source and outflow, Central Asian near-source, and a high-latitude source-is analyzed to provide information on its composition and variation. With respect to the importance of the mixing state, a single particle attempt was chosen. A particular focus of this study is the distribution of iron amongst individual particles, and its internal mixture with calcium compounds, as the iron compounds are of high interest for different processes. These processes include radiation absorption, photocatalytic reactions, and ocean fertilization.

A review of coarse mineral dust in the Earth system

“…Ultimately, atmospheric processing has an impact on the properties of mineral dust. Chemical aging can modify the dust hygroscopicity (e.g., Laskin et al, 2005;Tobo et al, 2010), henceforth its capability of acting as cloud or ice condensation nuclei (e.g., Levin and Ganor, 1996;Kulkarni et al, 2015;Kumar et al, 2011;Sullivan et al, 2009;Tang et al, 2016;Krueger et al, 2003) as well as its solubility in water, altering its fertilization capabilities for the oceans (e.g., Meskhidze et al, 2005;Paris et al, 2011;Shi et al, 2012;Kandler et al, 2020).…”

Newly identified climatically and environmentally significant high latitude dust sources

“…In the same area, near Longyearbyen, the presence of dust emissions from an active coal mine has been documented in Khan et al (2017). Kandler et al (2020) also report Svalbard measurements in Longyearbyen, in September 2017, with high iron and chlorite-like contributions in dust.…”

“…On the other hand, chemical-mineralogical investigation and single particle analysis made it possible to recognize and estimate the contribution of Icelandic dust in Ny-Alesund (Moroni et al, 2018). Kandler et al (2020) collected dry dust deposition near source in northwest Africa, in Central Asia, and on Svalbard and at three locations of the African outflow regime and studied particle sizes and composition. Their results showed low temporal variation in estimated optical properties for each location, but considerable differences between the African, Central Asian, and Arctic regimes.…”

A review of coarse mineral dust in the Earth system

“…Ultimately, atmospheric processing has an impact on the properties of mineral dust. Chemical aging can modify the dust hygroscopicity (e. g., Laskin et al, 2005;Tobo et al, 2010), henceforth its capability of acting as cloud or ice condensation nuclei (e.g., Levin and Ganor, 1996;Kulkarni et al, 2015;Kumar et al, 2011;Sullivan et al, 2009;Tang et al, 2016;Krueger et al, 2003) as well as its solubility in water, altering its fertilization capabilities for the oceans (e. g., Meskhidze et al, 2005;Paris et al, 2011;Shi et al, 2012;Kandler et al, 2020). The size of mineral dust particles conditions, directly and indirectly, its chemical aging, and the impacts on atmospheric chemistry that result from it.…”