TABLE OF CONTENTS Aerosols are, by their nature, multiphase, and equilibrium thermodynamics provides constraints and limiting conditions on particle interaction with the surrounding gas. Thermodynamic factors play a major role in atmospheric nucleation processes including fog and cloud formation. They are also important in the synthesis of small solid particles, affecting particle size and crystalline properties.
The ability of small particles to serve as condensation nuclei depends in a complex way on the thermodynamic path of the gas (pressure and temperature as a function of time), the vapor pressure curve, and the particle properties. Examples are given in this chapter of two common processes whose paths can lead to a supersaturated state, namely, isentropic expansion and the mixing of hot vapors with cold gases. The vapor pressure of a substance normally cited in the literature is the value in equilibrium with a planar surface of the material. However, a small particle suspended in the vapor may equilibrate with a vapor at a pressure that is larger or smaller than the planar equivalent value, depending on the particle surface tension, charge, and/or chemical composition. How these factors affect the equilibrium vapor pressure is reviewed in this chapter. The same factors that influence the particle equilibrium vapor pressure also reduce the melting temperature of small solid particles and affect the composition of a reacting gas mixture in equilibrium with small particles.
The thermodynamics of interacting clouds of molecular clusters is discussed at the end of this chapter. The equilibrium size distribution of the clusters...
