气候变化领域集成服务门户(CCPortal): Soot PCF: Pore condensation and freezing framework for soot aggregates

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DOI	10.5194/acp-21-7791-2021
	Soot PCF: Pore condensation and freezing framework for soot aggregates
	Marcolli C.; Mahrt F.; Kärcher B.
发表日期	2021
ISSN	1680-7316
起始页码	7791
结束页码	7843
卷号	21 期号:10
英文摘要	Atmospheric ice formation in cirrus clouds is often initiated by aerosol particles that act as ice-nucleating particles. The aerosol-cloud interactions of soot and associated feedbacks remain uncertain, in part because a coherent understanding of the ice nucleation mechanism and activity of soot has not yet emerged. Here, we provide a new framework that predicts ice formation on soot particles via pore condensation and freezing (PCF) that, unlike previous approaches, considers soot particle properties, capturing their vastly different pore properties compared to other aerosol species such as mineral dust. During PCF, water is taken up into pores of the soot aggregates by capillary condensation. At cirrus temperatures, the pore water can freeze homogeneously and subsequently grow into a macroscopic ice crystal. In the soot-PCF framework presented here, the relative humidity conditions required for these steps are derived for different pore types as a function of temperature. The pore types considered here encompass n-membered ring pores that form between n individual spheres within the same layer of primary particles as well as pores in the form of inner cavities that form between two layers of primary particles. We treat soot primary particles as perfect spheres and use the contact angle between soot and water (sw), the primary particle diameter (Dpp), and the degree of primary particle overlap (overlap coefficient, Cov) to characterize pore properties. We find that three-membered and four-membered ring pores are of the right size for PCF, assuming primary particle sizes typical of atmospheric soot particles. For these pore types, we derive equations that describe the conditions for all three steps of soot PCF, namely capillary condensation, ice nucleation, and ice growth. Since at typical cirrus conditions homogeneous ice nucleation can be considered immediate as soon as the water volume within the pore is large enough to host a critical ice embryo, soot PCF becomes limited by either capillary condensation or ice crystal growth. We use the soot-PCF framework to derive a new equation to parameterize ice formation on soot particles via PCF, based on soot properties that are routinely measured, including the primary particle size, overlap, and the fractal dimension. These properties, along with the number of primary particles making up an aggregate and the contact angle between water and soot, constrain the parameterization. Applying the new parameterization to previously reported laboratory data of ice formation on soot particles provides direct evidence that ice nucleation on soot aggregates takes place via PCF. We conclude that this new framework clarifies the ice formation mechanism on soot particles in cirrus conditions and provides a new perspective to represent ice formation on soot in climate models. © 2021 Author(s).
语种	英语
来源期刊	ATMOSPHERIC CHEMISTRY AND PHYSICS
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/246871
作者单位	Institute for Atmospheric and Climate Science, Department of Environmental Systems Science, ETH Zurich, Zurich, 8092, Switzerland; Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC V6T1Z1, Canada; Laboratory of Environmental Chemistry, Paul Scherrer Institute, Villigen, 5232, Switzerland; Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft-und Raumfahrt, DLR Oberpfaffenhofen, Weßling, 82234, Germany
推荐引用方式 GB/T 7714	Marcolli C.,Mahrt F.,Kärcher B.. Soot PCF: Pore condensation and freezing framework for soot aggregates[J],2021,21(10).
APA	Marcolli C.,Mahrt F.,&Kärcher B..(2021).Soot PCF: Pore condensation and freezing framework for soot aggregates.ATMOSPHERIC CHEMISTRY AND PHYSICS,21(10).
MLA	Marcolli C.,et al."Soot PCF: Pore condensation and freezing framework for soot aggregates".ATMOSPHERIC CHEMISTRY AND PHYSICS 21.10(2021).