Most human beings recognize the effects of evaporation, condensation, and gravity as phenomena happening everywhere in nature. Formation and the evaporation of tiny droplets on every flower or leaf is a routine spectacle around the planet. “Breath figures” or dew forms on windows or eye glasses;1 growth of breath figures on liquids,2 on solids,3, 4 and also the influence of wetting conditions in the formation of these figures on fibers5 are common phenomena of daily experience and of technological importance.

Evaporation of seawater, formation of clouds, and transformation of clouds into rain is one of the most important cycles of nature—the water cycle. In oceans the most important particle formation mechanism is condensation on soluble nuclei such as sodium chloride nuclei. They are formed in great numbers by the action of waves and bubbles. These nuclei exist throughout the global atmosphere. Salt dissolved in water raises its boiling point by lowering the equilibrium vapor pressure; therefore, droplet condensation in the gas phase occurs at a lower saturation ratio than in pure water. In additions, ions in the atmosphere promote particle formation and growth. This phenomenon is well observed in a Wilson cloud chamber,6 in which an alpha “particle” which travels a few centimeters through the air leaves behind a wake of thousands of air ions.

Research on aerosol production7 has led to the development of numerous droplet-generating devices,8 which have applications in many different areas of research such as agricultural spraying, spectroscopy, atomization, space operation, spray combustion, the perfume industry, etc. Industrial emissions of aerosols, including aircraft emissions, increase droplet concentration in clouds by increasing the number of particles and affect the nucleation of droplets of different types of clouds. The systematic use of sprays in agriculture causes the contamination of groundwater and of the aquifer systems of different types. These deceptively simple problems, which affect the continuity of humankind and life on the earth, are of considerable interest and pose important questions to be understood from studies in condensed matter physics, thermodynamics, and fluid dynamics.