An ice nucleus, also known as an ice nucleating particle (INP), is a particle which acts as the

nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: * Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...

for the formation of an

ice crystal Ice crystals are solid ice exhibiting atomic ordering on various length scales and include hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust. Formation The hugely symmetric shapes are due to depositional growth, n ...

in the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...

Ice Nucleation Mechanisms

There are a number of mechanisms of ice nucleation in the atmosphere through which ice nuclei can catalyse the formation of ice particles. In the upper

troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. Fro ...

, water vapor can deposit directly onto solid particles. In clouds warmer than about −37 °C where liquid water can persist in a

supercooled Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its melting point without it becoming a solid. It achieves this in the absence of a seed crystal or nucleus around which a crysta ...

state, ice nuclei can trigger droplets to freeze. Contact nucleation can occur if an ice nucleus collides with a supercooled droplet, but the more important mechanism of freezing is when an ice nucleus becomes immersed in a supercooled water droplet and then triggers freezing. In the absence of an ice nucleating particle, pure water droplets can persist in a supercooled state to temperatures approaching −37 °C where they freeze homogeneously. As per Web of Science, the key word "ice nucleation" that appeared under Met Atm Sci and Env Sci categories till Dec 2021 was plotted using number of papers published. Growth of number of papers with keyword Ice Nucleation

Growth of number of papers with keyword Ice Nucleation

There are several research groups that study ice nucleating properties of atmospheric aerosols (for example see FIN-02 research article by DeMott et al. 2018 o
The FIN-02 INP measurement intercomparison study
. The ice nucleation research capability is also available through user facility call at EMSL, PNNL (se
User facility
).

Cloud dynamics

Ice particles can have a significant effect on

cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...

dynamics. They are known to be important in the processes by which clouds can become electrified, which causes

lightning Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an average ...

. They are also known to be able to form the seeds for rain droplets. It has become clear that the concentration of ice nucleating particles in shallow clouds is a key factor in cloud-climate feedbacks.

Atmospheric particulate matter

Many different types of

atmospheric particulate matter Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The te ...

can act as ice nuclei, both natural and anthropogenic, including those composed of desert dust, soot, organic matter, bacteria (e.g. ''

Pseudomonas syringae ''Pseudomonas syringae'' is a rod-shaped, Gram-negative bacterium with polar flagella. As a plant pathogen, it can infect a wide range of species, and exists as over 50 different pathovars, all of which are available to researchers from inte ...

''), pollen, fungal spores and volcanic ash amongst others. However, the exact

nucleation In thermodynamics, nucleation is the first step in the formation of either a new thermodynamic phase or structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically defined to be the process that deter ...

potential of each type varies greatly, depending on the exact atmospheric conditions. Very little is known about the spatial distribution of these particles, their overall importance for global climate through ice cloud formation, and whether human activity has played a major role in changing these effects.

References

{{Authority control Cloud and fog physics Particulates

Ice Nucleation Mechanisms

Cloud dynamics

Atmospheric particulate matter

See also

References