Cloud condensation nuclei

Aerosol pollution over northern India and Bangladesh (Satellite image by NASA)

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.[1] 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.[2] 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.[3]

The concept of CCN is used in cloud seeding, which tries to encourage rainfall by seeding the air with condensation nuclei. It has further been suggested that creating such nuclei could be used for marine cloud brightening, a climate engineering technique.[4] 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.

  1. ^ "Formation of Haze, Fog, and Clouds: Condensation Nuclei". Retrieved 25 November 2014.
  2. ^ Hudson, James G. (1993-04-01). "Cloud Condensation Nuclei". Journal of Applied Meteorology and Climatology. 32 (4): 596–607. Bibcode:1993JApMe..32..596H. doi:10.1175/1520-0450(1993)032<0596:CCN>2.0.CO;2. ISSN 1520-0450.
  3. ^ National Research Council. Division on Earth and Life Studies, National Research Council. Board on Atmospheric Sciences and Climate, National Research Council. Ocean Studies Board (2015). Climate Intervention : reflecting sunlight to cool Earth. Washington, D.C. ISBN 978-0-309-31483-1. OCLC 914166140.{{cite book}}: CS1 maint: location missing publisher (link)
  4. ^ T., Houghton, J. (2001). Climate change 2001 the scientific basis. Cambridge University Press. ISBN 0-521-80767-0. OCLC 1295485860.{{cite book}}: CS1 maint: multiple names: authors list (link)