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The internal structure of Saharan dust revealed

The internal structure of Saharan dust revealed

FMI has been involved in a research project that has revealed the internal structure of Saharan dust.

Mineral dust particles, which are emitted in particular from deserts, are among the most important types of atmospheric particles to influence the Earth's radiative balance and atmospheric remote sensing. Ultimately, these impacts depend on the dust particle microphysical properties, including the particles' internal structures.

The internal structure of dust was first revealed in our pioneering study in 2014. The present study extends our pioneering study, which considered Asian dust, to dust originating from the Saharan desert. In the present study, the dust particles' internal structure was investigated by cutting thin, cross-sectional slices from the particles with a focused ion beam and then analyzing the slices with a transmission electron microscope. The analysis revealed that dust particles have abundance of internal structures. Compared to the Asian dust previously studied, however, the Saharan dust had fewer and smaller internal pores. Iron-rich minerals were commonly observed as small grains within the particles, which may enhance the biochemical availability of iron – dust is known to act as a fertilizer in iron-limited ecosystems such as surface ocean waters and the Amazonian rain forest.

Desert dust originates from eroding rocks and consists of tiny particles composed of a variety of different minerals. The particles suspended in the atmosphere are typically 0.01 mm or smaller in diameter. In the atmosphere, the dust particles have a range of impacts: they absorb, emit and scatter electromagnetic radiation; they take part in chemical reactions; and they act as freezing nuclei for ice clouds. Consequently, they influence Earth observations employing electromagnetic radiation, atmospheric radiative balance, atmospheric chemistry and the global water cycle. When deposited on the surface, they may serve as a source of nutrients and thereby influence the biosphere. Through these processes they influence the climate, and when inhaled, they may have adverse health effects.

The detailed characterization of dust particles allows for building realistic model dust particles whose interaction with electromagnetic radiation can then be solved accurately. This enables accurate and reliable identification and monitoring of dust e.g. with satellite instruments, making possible accurate determination of the global dust distribution. The impacts of dust can then be accurately accounted for e.g. in climate models. In addition, the impact of dust can be better corrected for in other atmospheric remote sensing in the presence of dust, improving their accuracy and reliability.

The research has been done in a collaboration between the Finnish Meteorological Institute, the Technical University of Darmstadt, the Kansas State University and the South Korea Andong National University.

Additional information:

Senior researcher Timo Nousiainen, tel +358 50 441 5451, timo.nousiainen@fmi.fi

G.Y. Jeong, M.Y. Park, K. Kandler, T. Nousiainen and O. Kemppinen (2016). Mineralogical properties and internal structures of individual fine particles of Saharan dust, Atmos. Chem. Phys., 16, 12397-12410, doi:10.5194/acp-16-12397-2016.



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