González-Flórez, Cristina ; Klose, Martina ; Alastuey, Andrés ; Dupont, Sylvain ; Escribano, Jerónimo ; Etyemezian, Vicken ; Gonzalez-Romero, Adolfo ; Huang, Yue ; Kandler, Konrad ; Nikolich, George ; Panta, Agnesh ; Querol, Xavier ; Reche, Cristina ; Yus-Díez, Jesús ; Pérez García-Pando, Carlos (2023)
Insights into the size-resolved dust emission from field measurements in the Moroccan Sahara.
In: Atmospheric Chemistry and Physics, 23 (12)
doi: 10.5194/acp-23-7177-2023
Article, Bibliographie

Abstract

The particle size distribution (PSD) of mineral dust has a strong effect on the impacts of dust on climate. However, our understanding of the emitted dust PSD, including its variability and the fraction of super-coarse dust (diameter >10 µm), remains limited. Here, we provide new insights into the size-resolved dust emission process based on a field campaign performed in the Moroccan Sahara in September 2019 in the context of the FRontiers in dust minerAloGical coMposition and its Effects upoN climaTe (FRAGMENT) project. The obtained dust concentration and diffusive flux PSDs show significant dependencies upon the friction velocity (u*), wind direction and type of event (regular events versus haboob events). For instance, the number fraction of sub-micrometre particles increases with u*, along with a large decrease in the mass fraction of super-coarse dust. We identify dry deposition, which is modulated by u* and fetch length, as a potential cause for this PSD variability. Using a resistance model constrained with field observations to estimate the dry deposition flux and thereby also the emitted dust flux, we show that deposition could represent up to ∼90% of the emission of super-coarse particles (>10 µm) and up to ∼65% of the emission of particles as small as ∼5 µm in diameter. Importantly, removing the deposition component significantly reduces the variability with u* in the PSD of the emitted dust flux compared with the diffusive flux, particularly for super-coarse dust. The differences between regular and haboob event concentration and diffusive flux PSDs are suspected to result from a smaller and variable dust source fetch during the haboob events, and/or an increased resistance of soil aggregates to fragmentation associated with the observed increase in relative humidity along the haboob outflow. Finally, compared to the invariant emitted dust flux PSD estimated based on brittle fragmentation theory, we obtain a substantially higher proportion of super-micrometre particles in the dust flux. Overall, our results suggest that dry deposition needs to be adequately considered to estimate the emitted PSD, even in studies limited to the fine and coarse size ranges (<10 µm).

Item Type:	Article
Erschienen:	2023
Creators:	González-Flórez, Cristina ; Klose, Martina ; Alastuey, Andrés ; Dupont, Sylvain ; Escribano, Jerónimo ; Etyemezian, Vicken ; Gonzalez-Romero, Adolfo ; Huang, Yue ; Kandler, Konrad ; Nikolich, George ; Panta, Agnesh ; Querol, Xavier ; Reche, Cristina ; Yus-Díez, Jesús ; Pérez García-Pando, Carlos
Type of entry:	Bibliographie
Title:	Insights into the size-resolved dust emission from field measurements in the Moroccan Sahara
Language:	English
Date:	2023
Place of Publication:	Göttingen
Publisher:	Copernicus Publications
Journal or Publication Title:	Atmospheric Chemistry and Physics
Volume of the journal:	23
Issue Number:	12
DOI:	10.5194/acp-23-7177-2023
Corresponding Links:	TUprints secondary publication Supplements Supplements
Abstract:	The particle size distribution (PSD) of mineral dust has a strong effect on the impacts of dust on climate. However, our understanding of the emitted dust PSD, including its variability and the fraction of super-coarse dust (diameter >10 µm), remains limited. Here, we provide new insights into the size-resolved dust emission process based on a field campaign performed in the Moroccan Sahara in September 2019 in the context of the FRontiers in dust minerAloGical coMposition and its Effects upoN climaTe (FRAGMENT) project. The obtained dust concentration and diffusive flux PSDs show significant dependencies upon the friction velocity (u*), wind direction and type of event (regular events versus haboob events). For instance, the number fraction of sub-micrometre particles increases with u*, along with a large decrease in the mass fraction of super-coarse dust. We identify dry deposition, which is modulated by u* and fetch length, as a potential cause for this PSD variability. Using a resistance model constrained with field observations to estimate the dry deposition flux and thereby also the emitted dust flux, we show that deposition could represent up to ∼90% of the emission of super-coarse particles (>10 µm) and up to ∼65% of the emission of particles as small as ∼5 µm in diameter. Importantly, removing the deposition component significantly reduces the variability with u* in the PSD of the emitted dust flux compared with the diffusive flux, particularly for super-coarse dust. The differences between regular and haboob event concentration and diffusive flux PSDs are suspected to result from a smaller and variable dust source fetch during the haboob events, and/or an increased resistance of soil aggregates to fragmentation associated with the observed increase in relative humidity along the haboob outflow. Finally, compared to the invariant emitted dust flux PSD estimated based on brittle fragmentation theory, we obtain a substantially higher proportion of super-micrometre particles in the dust flux. Overall, our results suggest that dry deposition needs to be adequately considered to estimate the emitted PSD, even in studies limited to the fine and coarse size ranges (<10 µm).
Alternative Abstract:	Alternative abstract Language Atmospheric mineral dust consists of tiny mineral particles that are emitted by wind erosion from arid regions. Its particle size distribution (PSD) affects its impact on the Earth's system. Nowadays, there is an incomplete understanding of the emitted dust PSD and a lot of debate about its variability. Here, we try to address these issues based on the measurements performed during a wind erosion and dust emission field campaign in the Moroccan Sahara within the framework of FRAGMENT project. English
Additional Information:	Special Issue: Dust aerosol measurements, modeling and multidisciplinary effects (AMT/ACP inter-journal SI)
Classification DDC:	500 Science and mathematics > 550 Earth sciences and geology 600 Technology, medicine, applied sciences > 624 Civil engineering and environmental protection engineering
Divisions:	11 Department of Materials and Earth Sciences 11 Department of Materials and Earth Sciences > Earth Science 11 Department of Materials and Earth Sciences > Earth Science > Atmospheric Aerosol
Date Deposited:	17 Jan 2024 09:11
Last Modified:	17 Jan 2024 09:11
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