"Condensation nuclei" refers to tiny particles or substances present in the air that facilitate the formation of water droplets, clouds, and precipitation. Full definition
The concentration of cloud condensation nuclei in the lower troposphere at a supersaturation of 1 percent ranges from around 100 per cubic centimetre (approximately 1,600 per cubic inch) in size in oceanic air to 500 per cubic centimetre (8,000 per cubic inch) in the atmosphere over a continent. (britannica.com)
Aerosols may influence climate in two ways: directly through scattering and absorbing radiation, and indirectly through acting as condensation nuclei for cloud formation or modifying the optical properties and lifetime of clouds (from the always useful IPCC glossary). (realclimate.org)
The moisture is also robbed from the western US and migrated east by excessive aerosol spraying (too many condensation nuclei for the cloud droplets to combine and fall as rain). (geoengineeringwatch.org)