This animation shows how a cloud is formed on the particle-level. Water droplets and black soot carbon aerosols mix in the air. Water droplets cling to aerosol particles, creating a larger water droplet. The droplet becomes very large and 'pops' into smaller water droplets, each with an aerosol particle inside, thus creating a cloud.
Aerosols are complex particles; they occur in nature and can also be generated by human activity. One important new area of aerosol research involves how aerosols impact clouds. Without aerosols, clouds could not exist. Aerosol particles serve as condensation nuclei for water vapor in the atmosphere. Atmospheric water molecules are drawn to aerosol particles like magnets, forming water droplets and eventually creating a cloud. The introduction of a larger number of aerosols will modify cloud's natural properties, leading to an accumulation of water droplets that are smaller in size but greater in number. Clouds play an important role in regulating Earth's climate; aerosol-rich air masses generate clouds that are bigger, brighter, and longer lasting.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 126.96.36.199.0