condensation nuclei

in atmospheric chemistry
https://doi.org/10.1351/goldbook.C01236
Particles, either liquid or solid, or ions upon which condensation of water vapour (or other substances) begins in the atmosphere. Condensation nuclei are usually very small hygroscopic aerosols (\(0.001\ \unicode[Times]{x3BC}\text{m}\) to \(0.1\ \unicode[Times]{x3BC}\text{m}\) in diameter), but these are not as abundant as the smaller particles. The number of CN which are active (initiate condensation) in a given air mass may be a function of the @R05267@. Usually CN are counted as the active nuclei at about 300% @R05267@, while cloud condensation nuclei (CCN) are counted as the number of active nuclei at @R05267@ less than or equal to 102%.
Source:
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2182 [Terms] [Paper]