TY  - JOUR
A1  - Boose, Yvonne
A1  - Welti, André
A1  - Atkinson, James
A1  - Ramelli, Fabiola
A1  - Danielczok, Anja
A1  - Bingemer, Heinz
A1  - Plötze, Michael
A1  - Sierau, Berko
A1  - Kanji, Zamin A.
A1  - Lohmann, Ulrike
T1  - Heterogeneous ice nucleation on dust particles sourced from 9
deserts worldwide - Part 1: Immersion freezing
T2  - Atmospheric chemistry and physics. Discussions
N2  - Desert dust is one of the most abundant ice nucleating particle types in the atmosphere. Tra ditionally, clay minerals were assumed to determine the ice nucleation ability of desert dust and constituted the focus of ice nucleation studies. Only recently some feldspar species were identified to be ice-active at much higher temperatures than clay minerals, redirecting studies to investigate the contribution of feldspar to ice nucleation on desert dust. However, so far no study has shown the atmospheric relevance of this mineral phase.
For this study four dust samples were collected after airborne transport in the troposphere from the Sahara to different locations (Crete, the Peloponnese, Canary Islands and the Sinai Peninsula). Additionally, eleven dust samples were collected from the surface from nine of the biggest deserts worldwide. The samples were used to study the ice nucleation behavior specific to different desert dusts. Furthermore we investigated how representative ice nucleation on surface-collected dust is for that in the atmosphere by comparing to the ice nucleation activity of the airborne samples. We used the IMCA-ZINC set-up to form droplets on single aerosol particles which were subsequently exposed to temperatures between 233 - 250 K. Dust particles were collected in parallel on filters for offline cold stage ice nucleation experiments at 253 - 263 K. To help the interpretation of the results from the ice nucleation experiments the mineralogical composition of the dusts was investigated.We found that a higher ice nucleation activity in a given sample can be attributed at 253 K to the K-feldspar content present in this sample whereas at temperatures between 238 - 245 K it is attributed to the sum of feldspar and quartz content present. A high clay content on the other hand is associated with a lower ice nucleation activity of a sample. This confirms the importance of feldspar at T > 250 K and the role of quartz and feldspars determining the ice nucleation activities at lower T as found by earlier studies for monomineral dust surrogates. Furthermore, we find that milling may lead to a decrease in the ice nucleation ability of polymineral samples due to a change in mineralogical composition in the atmospherically relevant size fraction arising from the different hardness and cleavage of individual mineral phases. Comparison of our comprehensive data set to an existing desert dust parameterization confirms its applicability for climate models. Our results suggest that for an improved prediction of the ice nucleation ability of desert dust in the atmosphere, the modelling of emission and atmospheric transport of the feldspar and quartz mineral phases would be key while other minerals are only of minor importance.
Y1  - 2016
UR  - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/42612
UR  - https://nbn-resolving.org/urn:nbn:de:hebis:30:3-426121
SN  - 1680-7375
N1  - © Author(s) 2016. This work is distributed under the Creative Commons Attribution 3.0 License.
VL  - 16
IS  - 438
SP  - 1
EP  - 32
PB  - European Geosciences Union
CY  - Katlenburg-Lindau.
ER  -