10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Ice-Nucleating Properties of Coal Fly Ash Particles in Cirrus Cloud Conditions
NSIKANABASI UMO, Robert Wagner, Romy Ullrich, Kristina Höhler, Naruki Hiranuma, Amanda Lea-Langton, Harald Saathoff, Alexei Kiselev, Peter G. Weidler, Heike Wex, Sarah Grawe, Jenny M. Jones, Alan Williams, Benjamin Murray, Thomas Leisner, Ottmar Möhler, Karlsruhe Institute of Technology
Abstract Number: 855 Working Group: Unraveling the Many Facets of Ice Nucleating Particles and Their Interactions with Clouds
Abstract Globally, over 600 Tg of coal fly ash (CFA) are produced annually from coal combustion for industrial and domestic energy production. A certain proportion of these aerosol particles is emitted to the atmosphere and may impact air quality, human health, and radiative transfer through the atmosphere. Coal fly ash can also modify cloud microphysical and optical properties, hence influencing the climatic and the hydrological cycles. However, our understanding of the role of CFA in nucleating ice at conditions relevant to cirrus clouds is lacking and requires research efforts. Here, we investigate the ice-nucleating properties of CFA, obtained from four different sources, in the deposition mode at the AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud simulation chamber. All the CFA samples (particle median diameter ~ 0.6 µm) showed significant ice nucleation activity at ice saturation ratios between 1.04 and 1.38 evaluated at the maximum relative humidity with respect to ice reached during each experiment, in the temperature range from 214 K to 251 K. The ice nucleation active surface site densities of these particles in the deposition mode were estimated between 109 - 1011 m-2 within the same temperature coverage of the experiment. One of the CFA samples studied in this work showed high ice nucleation activity at even lower ice saturation ratios (1.04 - 1.16) at ~ 228K, which suggests that pore condensation and freezing may be the dominant ice formation mechanism as there was no corresponding high activity of this particular CFA in the immersion freezing mode. The results from this study have clearly established that CFA aerosol particles efficiently nucleate ice in the deposition mode. Future study should focus on probing the factors driving their ice-nucleating abilities. CFA particles may contribute to cloud ice formation, in particular, close to the source region where these particles are emitted directly into the atmosphere. Also, future modelling and experimental studies are needed to further investigate and assess the abundance of CFA aerosols and their contribution to cloud ice formation on regional and global scales.