Cloud condensation nuclei
Also called: CCN, Hygroscopic nuclei, Hygroscopic condensation nuclei, Condensation nuclei · Topic: Water in the Atmosphere: Humidity, Condensation, Clouds and Precipitation · NCERT: Class 11, Ch 7 "Composition and Structure of Atmosphere"; Class 11, Ch 10 "Water in the Atmosphere"
Meaning
Cloud condensation nuclei (CCN) are tiny particles in the air, such as dust, smoke and sea salt. They are hygroscopic, which means they attract water. Water vapour condenses on them to form the droplets of clouds and fog. Without them, droplets would form only when the air held far more vapour than it normally can, which is very high supersaturation. So more particles in the air can mean more fog and smog. Cloud seeding with salt particles uses the same idea to help droplets grow in warm clouds.
Example
In winter, smoke and dust over Delhi give water vapour countless nuclei to condense on. This helps form the thick smog that hangs over the city.
Don't confuse with
- Ice nuclei: these help ice crystals form in cold clouds. Silver iodide is used for this in cloud seeding. CCN help liquid droplets form.