Articles | Volume 23, issue 12
Research article
 | Highlight paper
20 Jun 2023
Research article | Highlight paper |  | 20 Jun 2023

Particle shapes and infrared extinction spectra of nitric acid dihydrate (NAD) crystals: optical constants of the β-NAD modification

Robert Wagner, Alexander D. James, Victoria L. Frankland, Ottmar Möhler, Benjamin J. Murray, John M. C. Plane, Harald Saathoff, Ralf Weigel, and Martin Schnaiter

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High homogeneous freezing onsets of sulfuric acid aerosol at cirrus temperatures
Julia Schneider, Kristina Höhler, Robert Wagner, Harald Saathoff, Martin Schnaiter, Tobias Schorr, Isabelle Steinke, Stefan Benz, Manuel Baumgartner, Christian Rolf, Martina Krämer, Thomas Leisner, and Ottmar Möhler
Atmos. Chem. Phys., 21, 14403–14425,,, 2021
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Heterogeneous ice nucleation ability of aerosol particles generated from Arctic sea surface microlayer and surface seawater samples at cirrus temperatures
Robert Wagner, Luisa Ickes, Allan K. Bertram, Nora Els, Elena Gorokhova, Ottmar Möhler, Benjamin J. Murray, Nsikanabasi Silas Umo, and Matthew E. Salter
Atmos. Chem. Phys., 21, 13903–13930,,, 2021
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Ice nucleation ability of ammonium sulfate aerosol particles internally mixed with secondary organics
Barbara Bertozzi, Robert Wagner, Junwei Song, Kristina Höhler, Joschka Pfeifer, Harald Saathoff, Thomas Leisner, and Ottmar Möhler
Atmos. Chem. Phys., 21, 10779–10798,,, 2021
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High-resolution optical constants of crystalline ammonium nitrate for infrared remote sensing of the Asian Tropopause Aerosol Layer
Robert Wagner, Baptiste Testa, Michael Höpfner, Alexei Kiselev, Ottmar Möhler, Harald Saathoff, Jörn Ungermann, and Thomas Leisner
Atmos. Meas. Tech., 14, 1977–1991,,, 2021
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The ice-nucleating activity of Arctic sea surface microlayer samples and marine algal cultures
Luisa Ickes, Grace C. E. Porter, Robert Wagner, Michael P. Adams, Sascha Bierbauer, Allan K. Bertram, Merete Bilde, Sigurd Christiansen, Annica M. L. Ekman, Elena Gorokhova, Kristina Höhler, Alexei A. Kiselev, Caroline Leck, Ottmar Möhler, Benjamin J. Murray, Thea Schiebel, Romy Ullrich, and Matthew E. Salter
Atmos. Chem. Phys., 20, 11089–11117,,, 2020
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Related subject area

Subject: Aerosols | Research Activity: Laboratory Studies | Altitude Range: Stratosphere | Science Focus: Physics (physical properties and processes)
Ice-nucleating ability of particulate emissions from solid-biomass-fired cookstoves: an experimental study
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Cited articles

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Barton, N., Rowland, B., and Devlin, J. P.: Infrared-Spectra of Large Acid Hydrate Clusters – Formation Conditions of Submicron Particles of HNO3 2H2O and HNO3 3H2O, J. Phys. Chem., 97, 5848–5851, 1993. 
Benz, S., Megahed, K., Möhler, O., Saathoff, H., Wagner, R., and Schurath, U.: T-dependent rate measurements of homogeneous ice nucleation in cloud droplets using a large atmospheric simulation chamber, J. Photochem. Photobio. A, 176, 208–217, 2005. 
Bertozzi, B.: Ice nucleation ability of secondary aerosol particles at cirrus cloud conditions, PhD, Department of Physics, Karlsruhe Institute of Technology, Karlsruhe,, 2021. 
Executive editor
Polar Stratospheric Clouds (PSCs) catalyze ozone depletion at high latitudes with important impacts on energetic, biologically effective UV radiation. The present study is a unique experiment into PSC particle optical properties and formation performed in a large, coolable cloud chamber. Robert Wagner and his colleagues find evidence that a nitric acid dihydrate can be efficiently crystallized in PSCs through heterogeneous nucleation, for example by mineral dust or micrometeorites. It has a "beta-polymorph" crystalline structure - with distinct optical properties - clearly separable from an alpha-polymorph that forms at low temperatures through homogeneous nucleation. Interestingly, electron microscopy, infrared spectroscopy, X-ray diffraction and calculations all point to the same conclusion. The results have important implications for our understanding and the detection of PSCs.
Short summary
Polar stratospheric clouds (PSCs) play an important role in the depletion of stratospheric ozone. They can consist of different chemical species, including crystalline nitric acid hydrates. We found that mineral dust or meteoric ablation material can efficiently catalyse the formation of a specific phase of nitric acid dihydrate crystals. We determined predominant particle shapes and infrared optical properties of these crystals, which are important inputs for remote sensing detection of PSCs.
Final-revised paper