Approximation Formulas for the Equilibrium Size of an Aerosol Particle as a Function of Its Dry Size and Composition and the Ambient Relative Humidity

Approximations to the exact equations describing the variation with relative humidity of the equilibrium size of aqueous solution droplets are developed. For relative humidities between 81 and 99.5%, and for droplets formed by particles composed of greater than 60% by mass of any one of nine common electrolytes and having a dry radius in the range of 0.05 to 3.0 μm, the approximation formulas presented are accurate to within 5%. Using these formulas, an expression is obtained for the size distribution of a chemically homogeneous aerosol as a function of relative humidity.