Water molecules in the atmosphere are too small to combine on their own to form cloud droplets. To form condensation, they need something larger to condense on (preferably flatter surface and at least one micrometer in size). That’s where cloud condensation nuclei (CCN) come in, otherwise known as cloud seeds.

 

Cloud seeds, or cloud condensation nuclei (CCN), are created by new particle formation (NPF), which are created by even smaller particles forming together.

 

“Nucleation” sums up this process, where extremely small aerosol particles form larger particles in the sky. 

 

The scale of nucleation in the atmosphere ranges in the pico-/nano- scale of measurement. NPF may sometimes begin as tiny as picoparticles, build into nanoparticles, then cluster into bigger microparticles.

 

Atmospheric nanoparticles are referred to as Aitken nuclei by The American Meteorological Society (named after John Aitken).

 

• "It's easier for water vapor to condense into water droplets when it has a particle to condense upon. These particles, such as dust and pollen, are called condensation nuclei. Eventually, enough water vapor condenses on pieces of dust, pollen, and other condensation nuclei to form a cloud." Clouds and How They Form​

• “There are two ingredients needed for clouds to form: water and nuclei.” How Clouds Form​

• “The smallest long lived nanoparticles in the atmosphere (radius<2 nm) condense from evaporated meteoric material in the mesopause region (h~85 km).” KIT- Atmospheric Aerosol Research​​

• “Atmospheric nanoparticles can be formed either via nucleation in atmosphere or be directly emitted to the atmosphere.” Overview of Sources and Characteristics of Nanoparticles in Urban Traffic-Influenced Areas​

• An invention for cloud seeding using nanotechnology, involving graphene oxide and silica dioxide nanoparticles: “3d reduced graphene oxide/sio 2 composite for ice nucleation”

• Scientists advance cloud-seeding capabilities with nanotechnology

• National Center of Meteorology: UAE Rain Enhancement Program on the use of (titanium dioxide) salt/TiOz core-shell nanoparticles in the sky

• Using nanotechnology to accelerate the water condensation nucleation and growth for rain enhancement

• Nucleation and Growth of Nanoparticles in the Atmosphere

• Journal of Aerosol Science- A tutorial guide on new particle formation experiments using a laminar flow reactor​

• Patent: Laminar microjet atomizer and method of aerial spraying of liquids

• "The hygroscopic seeding material was detected in cloud droplets" CAIPEEX: Indian Cloud Seeding Scientific Experiment (2023)

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​"Releasing charge into natural droplet systems such as fog and clouds offers a route to influence their properties. To facilitate charge release across a wide range of altitudes and meteorological circumstances—such as developing clouds—a charge emitter has been developed for integration with the conventional cloud-seeding flares carried by crewed cloud-seeding aircraft. This allows charge emitters to be used alongside, or instead of, conventional particle releasing flares.”