Aerosols are complex particles; they can occur in nature but can also be generated by humans. One source of naturally-occurring aerosols is the ocean-wave activity which propels salt particles into the air. These particles then serve as cloud condensation nuclei and lead to cloud formation. Sea salt still image courtesy of Chere Petty, University of Maryland, Baltimore County; NSF grant DBI-0722569
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 8.0.0.0.0