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Ice nucleation ability of ammonium sulfate aerosol particles internally mixed with secondary organics

The abundance of aerosol particles and their ability to catalyze ice nucleation are key parameters to correctly understand and describe the aerosol indirect effect on the climate. Cirrus clouds strongly influence the Earth’s radiative budget, but their effect is highly sensitive to their formation m...

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Autores principales: Bertozzi, Barbara, Wagner, Robert, Song, Junwei, Höhler, Kristina, Pfeifer, Joschka, Saathoff, Harald, Leisner, Thomas, Möhler, Ottmar
Lenguaje:eng
Publicado: 2021
Materias:
Acceso en línea:https://dx.doi.org/10.5194/acp-21-10779-2021
http://cds.cern.ch/record/2808730
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author Bertozzi, Barbara
Wagner, Robert
Song, Junwei
Höhler, Kristina
Pfeifer, Joschka
Saathoff, Harald
Leisner, Thomas
Möhler, Ottmar
author_facet Bertozzi, Barbara
Wagner, Robert
Song, Junwei
Höhler, Kristina
Pfeifer, Joschka
Saathoff, Harald
Leisner, Thomas
Möhler, Ottmar
author_sort Bertozzi, Barbara
collection CERN
description The abundance of aerosol particles and their ability to catalyze ice nucleation are key parameters to correctly understand and describe the aerosol indirect effect on the climate. Cirrus clouds strongly influence the Earth’s radiative budget, but their effect is highly sensitive to their formation mechanism, which is still poorly understood. Sulfate and organics are among the most abundant aerosol components in the troposphere and have also been found in cirrus ice crystal residuals. Most of the studies on ice nucleation at cirrus cloud conditions looked at either purely inorganic or purely organic particles. However, particles in the atmosphere are mostly found as internal mixtures, the ice nucleation ability of which is not yet fully characterized. In this study, we investigated the ice nucleation ability of internally mixed particles composed of crystalline ammonium sulfate (AS) and secondary organic material (SOM) at temperatures between −50 and −65 ◦C. The SOM was generated from the ozonolysis of α-pinene. The experiments were conducted in a large cloud chamber, which also allowed us to simulate various aging processes that the particles may experience during their transport in the atmosphere, like cloud cycling and redistribution of the organic matter. We found that the ice nucleation ability of the mixed AS / SOM particles is strongly dependent on the particle morphology. Small organic mass fractions of 5 wt %–8 wt % condensed on the surface of AS crystals are sufficient to completely suppress the ice nucleation ability of the inorganic component, suggesting that the organic coating is evenly distributed on the surface of the seed particles. In this case, the ice nucleation onset increased from a saturation ratio with respect to ice Sice ∼ 1.30 for the pure AS crystals to ≥ 1.45 for the SOM-coated AS crystals. However, if such SOM-coated AS crystals are subjected to the mentioned aging processes, they show an improved ice nucleation ability with the ice nucleation onset at Sice ∼ 1.35. We suggest that the aging processes change the particle morphology. The organic matter might redistribute on the surface to form a partially engulfed structure, where the ice-nucleation-active sites of the AS crystals are no longer completely masked by the organic coating, or the morphology of the organic coating layer might transform from a compact to a porous structure. Our results underline the complexity in representing the ice nucleation ability of internally mixed particles in cloud models. They also demonstrate the need to further investigate the impact of atmospheric aging and cloud processing on the morphology and related ice nucleation ability of internally mixed particles.
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institution Organización Europea para la Investigación Nuclear
language eng
publishDate 2021
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spelling cern-28087302022-11-01T21:13:30Zdoi:10.5194/acp-21-10779-2021http://cds.cern.ch/record/2808730engBertozzi, BarbaraWagner, RobertSong, JunweiHöhler, KristinaPfeifer, JoschkaSaathoff, HaraldLeisner, ThomasMöhler, OttmarIce nucleation ability of ammonium sulfate aerosol particles internally mixed with secondary organicsChemical Physics and ChemistryThe abundance of aerosol particles and their ability to catalyze ice nucleation are key parameters to correctly understand and describe the aerosol indirect effect on the climate. Cirrus clouds strongly influence the Earth’s radiative budget, but their effect is highly sensitive to their formation mechanism, which is still poorly understood. Sulfate and organics are among the most abundant aerosol components in the troposphere and have also been found in cirrus ice crystal residuals. Most of the studies on ice nucleation at cirrus cloud conditions looked at either purely inorganic or purely organic particles. However, particles in the atmosphere are mostly found as internal mixtures, the ice nucleation ability of which is not yet fully characterized. In this study, we investigated the ice nucleation ability of internally mixed particles composed of crystalline ammonium sulfate (AS) and secondary organic material (SOM) at temperatures between −50 and −65 ◦C. The SOM was generated from the ozonolysis of α-pinene. The experiments were conducted in a large cloud chamber, which also allowed us to simulate various aging processes that the particles may experience during their transport in the atmosphere, like cloud cycling and redistribution of the organic matter. We found that the ice nucleation ability of the mixed AS / SOM particles is strongly dependent on the particle morphology. Small organic mass fractions of 5 wt %–8 wt % condensed on the surface of AS crystals are sufficient to completely suppress the ice nucleation ability of the inorganic component, suggesting that the organic coating is evenly distributed on the surface of the seed particles. In this case, the ice nucleation onset increased from a saturation ratio with respect to ice Sice ∼ 1.30 for the pure AS crystals to ≥ 1.45 for the SOM-coated AS crystals. However, if such SOM-coated AS crystals are subjected to the mentioned aging processes, they show an improved ice nucleation ability with the ice nucleation onset at Sice ∼ 1.35. We suggest that the aging processes change the particle morphology. The organic matter might redistribute on the surface to form a partially engulfed structure, where the ice-nucleation-active sites of the AS crystals are no longer completely masked by the organic coating, or the morphology of the organic coating layer might transform from a compact to a porous structure. Our results underline the complexity in representing the ice nucleation ability of internally mixed particles in cloud models. They also demonstrate the need to further investigate the impact of atmospheric aging and cloud processing on the morphology and related ice nucleation ability of internally mixed particles.oai:cds.cern.ch:28087302021
spellingShingle Chemical Physics and Chemistry
Bertozzi, Barbara
Wagner, Robert
Song, Junwei
Höhler, Kristina
Pfeifer, Joschka
Saathoff, Harald
Leisner, Thomas
Möhler, Ottmar
Ice nucleation ability of ammonium sulfate aerosol particles internally mixed with secondary organics
title Ice nucleation ability of ammonium sulfate aerosol particles internally mixed with secondary organics
title_full Ice nucleation ability of ammonium sulfate aerosol particles internally mixed with secondary organics
title_fullStr Ice nucleation ability of ammonium sulfate aerosol particles internally mixed with secondary organics
title_full_unstemmed Ice nucleation ability of ammonium sulfate aerosol particles internally mixed with secondary organics
title_short Ice nucleation ability of ammonium sulfate aerosol particles internally mixed with secondary organics
title_sort ice nucleation ability of ammonium sulfate aerosol particles internally mixed with secondary organics
topic Chemical Physics and Chemistry
url https://dx.doi.org/10.5194/acp-21-10779-2021
http://cds.cern.ch/record/2808730
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