Cloud microphysics; Ice crystal formation; Fresh and aged mineral dust aerosols; Laboratory studies
Nagare Baban, Marcolli Claudia, Welti Andre, Stetzer Olaf, Lohmann Ulrike (2016), Comparing contact and immersion freezing from continuous flow diffusion chambers, in Atmospheric Chemistry and Physics
, 16, 8899-8914.
Boose Yvonne, Kanji Zamin A., Kohn Monika, Sierau Berko, Zipori Assaf, Crawford Ian, Lloyd Gary, Bukowiecki Nicolas, Herrmann Erik, Kupiszewski Piotr, Steinbacher Martin, Lohmann Ulrike (2016), Ice Nucleating Particle Measurements at 241 K during Winter Months at 3580 m MSL in the Swiss Alps, in Journal of the Atmospheric Sciences
, 73, 2203-2228.
Boose Yvonne, Sierau Berko, Garcia Isabel M, Rodríguez Sergio, Alastuey Andrés, Linke Claudia, Schnaiter Martin, Kupiszewski Piotr, Kanji Zamin A, Lohmann Ulrike (2016), Ice nucleating particles in the Saharan Air Layer, in Atmospheric Physics and Chemistry
, 16, 9067-9087.
Marcolli Claudia, Nagare Baban, Welti Andre, Lohmann Ulrike (2016), Ice nucleation efficiency of AgI: review and new insights, in Atmospheric Chemistry and Physics
, 2016, 8915-8937.
Nagare Baban, Marcella Claudia, Stetzer Olaf, Lohmann Ulrike (2015), Comparison of measured and calculated collision efficiencies at low temperatures, in Atmospheric Chemistry and Physics
, 15, 13759-13776.
Kanji Zamin A., Welti Andre, Chou Cedric, Stetzer Olaf, Lohmann Ulrike (2013), Laboratory studies of immersion and deposition mode ice nucleation of ozone aged mineral dust particles, in Atmospheric Chemistry and Physics
, 13, 909-9118.
Boose Yvonne, Welti Andre, Atkinson James, Ramelli Fabiola, Danielczok Anja, Bingemer Heinz G., Plötze Michael, Sierau Berko, Kanji Zamin A., Lohmann Ulrike, Heterogeneous ice nucleation on dust particles sourced from 9 deserts worldwide – Part 1: Immersion freezing, in Atmospheric Chemistry and Physics
, Accepted(N/A), N/A-N/A.
Clouds can be composed of ice crystals and/or water droplets. The relative abundance, sizes and shapes of these hydrometeors determine the radiative properties of clouds. The Earth’s climate is a strong function of the balance of incoming and outgoing radiation and therefore if cloud composition changes due to anthropogenic emissions it is important to assess the climate impact of these emissions. A detailed knowledge of all underlying and contributing processes to the radiative balance is necessary for this assessment. Ice in clouds forms via homogeneous and heterogeneous ice nucleation. For the latter, insoluble particles termed ice nuclei (IN) are required as catalysts to aid the ice formation process. Of the four heterogeneous ice nucleation processes, contact freezing is the least understood mechanism for which only limited experimental data is available. One reason for this is that contact freezing is a two-step process and to fully understand and quantify contact freezing, both steps need to be treated and preferentially measured independently. The two steps are the collision of a droplet with an aerosol particle, followed by the freezing of the droplet as a result of the collision, which in turn depends on ambient temperature conditions. Ultimately, a full microphysical characterization of an ice nucleus in all heterogeneous nucleation modes is needed to improve our understanding of the relative importance of the different nucleation modes for cloud formation processes.The most important IN in the atmosphere are mineral dust particles originating from desert regions such as the Sahara and Gobi deserts. Through anthropogenic activities, reactive trace gases such as O3, SO2, and NOx (nitric oxides) can be emitted into the atmosphere either directly or be formed by secondary processes caused by emissions of precursors. These reactive trace gases can also interact with existing particles like mineral dust and modify their properties such as hygroscopicity and chemical composition such that they can aid warm cloud formation by acting as condensation nuclei (CCN) or cold cloud formation by acting as IN. Motivated by such interactions in the troposphere we propose the following research objectives for this project: 1.To better quantify the collision of an aerosol particle with a supercooled droplet, using systematic laboratory measurements of the collisions between droplets and particles2.To measure contact freezing experimentally and infer from these the experiment-independent particle property “freezing efficiency” by using the data from objective 1 to de-convolve the collision from the freezing step in contact freezing.3.To quantify how reactions with trace gases modify the properties of dust samples (surrogates and Saharan dust sampled from the atmosphere) and their abilities to act as CCN and IN in all four heterogeneous ice nucleation modes.4.To characterize airborne Saharan dust sampled from the atmosphere chemically, physically, and mineralogically complementing the experiments mentioned under objective 3.