Cloud condensation nuclei
small particle (typically 0.2 µm) on which water vapor condenses
Cloud condensation nuclei (CCNs), also known as cloud seeds, are small particles typically 0.2 μm, or one hundredth the size of a cloud droplet. CCNs are a unique subset of aerosols in the atmosphere on which water vapour condenses. This can affect the radiative properties of clouds and the overall atmosphere. Water vapour requires a non-gaseous surface to make the transition to a liquid; this process is called condensation.
In the atmosphere of Earth, this surface presents itself as tiny solid or liquid particles called CCNs. When no CCNs are present, water vapour can be supercooled at about −13 °C (9 °F) for 5–6 hours before droplets spontaneously form. This is the basis of the cloud chamber for detecting subatomic particles.
The concept of CCN (must associate to a supersaturation ratio) is used in cloud seeding, which tries to encourage rainfall by seeding the air with condensation nuclei (CN, which does not associate to supersaturation ratio). It has further been suggested that creating such nuclei could be used for marine cloud brightening, a climate engineering technique. Some natural environmental phenomena, such as the one proposed in the CLAW hypothesis also arise from the interaction between naturally produced CCNs and cloud formation.
The public source identifies “Cloud condensation nuclei” as small particle (typically 0.2 µm) on which water vapor condenses. This brief keeps that definition visible, then builds a research path around Cloud, condensation and nuclei.
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Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Jul 17, 2026. The linked authority identifier is Q906347. The Library of Congress control number is sh85009286. 1 of 1 selected statements include explicit references; 1 carry qualifiers and 0 use preferred rank.
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This entry incorporates text from “Cloud condensation nuclei” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.