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Volume 16, issue 21
Atmos. Chem. Phys., 16, 13911–13928, 2016
https://doi.org/10.5194/acp-16-13911-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Results from the ice nucleation research unit (INUIT) (ACP/AMT...

Atmos. Chem. Phys., 16, 13911–13928, 2016
https://doi.org/10.5194/acp-16-13911-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 10 Nov 2016

Research article | 10 Nov 2016

The immersion freezing behavior of ash particles from wood and brown coal burning

Sarah Grawe1, Stefanie Augustin-Bauditz1, Susan Hartmann1, Lisa Hellner1, Jan B. C. Pettersson2, Andrea Prager3, Frank Stratmann1, and Heike Wex1 Sarah Grawe et al.
  • 1Leibniz Institute for Tropospheric Research, Leipzig, Germany
  • 2Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
  • 3Leibniz Institute of Surface Modification, Leipzig, Germany

Abstract. It is generally known that ash particles from coal combustion can trigger ice nucleation when they interact with water vapor and/or supercooled droplets. However, data on the ice nucleation of ash particles from different sources, including both anthropogenic and natural combustion processes, are still scarce. As fossil energy sources still fuel the largest proportion of electric power production worldwide, and biomass burning contributes significantly to the global aerosol loading, further data are needed to better assess the ice nucleating efficiency of ash particles. In the framework of this study, we found that ash particles from brown coal (i.e., lignite) burning are up to 2 orders of magnitude more ice active in the immersion mode below −32 °C than those from wood burning. Fly ash from a coal-fired power plant was shown to be the most efficient at nucleating ice. Furthermore, the influence of various particle generation methods on the freezing behavior was studied. For instance, particles were generated either by dispersion of dry sample material, or by atomization of ash–water suspensions, and then led into the Leipzig Aerosol Cloud Interaction Simulator (LACIS) where the immersion freezing behavior was examined. Whereas the immersion freezing behavior of ashes from wood burning was not affected by the particle generation method, it depended on the type of particle generation for ash from brown coal. It was also found that the common practice of treating prepared suspensions in an ultrasonic bath to avoid aggregation of particles led to an enhanced ice nucleation activity. The findings of this study suggest (a) that ash from brown coal burning may influence immersion freezing in clouds close to the source and (b) that the freezing behavior of ash particles may be altered by a change in sample preparation and/or particle generation.

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Short summary
In this study the freezing behavior of ash particles immersed in supercooled cloud droplets was investigated. It was found that ash from coal burning initiates freezing well above the limit for homogeneous ice nucleation and may contribute to cloud glaciation and precipitation formation on a regional scale. Furthermore, the experimental results were influenced by a change in sample preparation and/or particle generation which must be accounted for when comparing to previous studies.
In this study the freezing behavior of ash particles immersed in supercooled cloud droplets was...
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