Cloud Condensation Nuclei. Condensed water vapor that is so small that it can only be seen through a microscope. CCN are actually the center of the droplet. Many of these nuclei are tiny salt particles, sulfate or nitrate aerosol, or small particles present in smoke. See dimethyl sulfide. Most droplets measure from 1/2,500 to 1/250 inch (0.01 to 0.1 millimeter) in diameter. [Journal of Applied Meteorology. v 32, 666, 1993.] [Journal of Aerosol Science. v 23 supp. page S865, 1992.] Coarse Mode Particles - are particles that are larger than two ïm in diameter. They come form sea sprays, volcanoes, crushing or grinding of rocks, wind blown soil, and account for about 95% of the aerosol particles in ambient air.