Radius and refractive index of aqueous inorganic aerosol particles: Accurate approximations for dependence on relative humidity. Lewis E. and Schwartz S. E. 15th ARM Science Team Meeting. Daytona Beach FL. March 14-17, 2005.

The direct influence of aerosol particles on atmospheric radiation through light scattering is determined by their radii and refractive indices, both of which are affected by uptake of water vapor. Previous expressions for these quantities have typically been given in terms of molality or solute mole or mass fraction rather than relative humidity RH, which is the pertinent atmospheric variable. Accurate treatment of the dependencies of these quantities on RH requires consideration also of particle mass (or, equivalently, dry radius) to account for influences of surface tension (Kelvin effect). Here simple expressions are presented for the dependence of radius and index of refraction on RH for a particle of given dry mass, for several inorganic salts and acids of atmospheric importance. These expressions, which are accurate to a few percent over a wide range of RH, are readily applicable in radiation transfer models and climate models.


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