Effective Refractive Index Values and Single Scattering Albedo Implications for Dry-Generated Clays As Retrieved from Cavity Ring-Down Spectroscopy

Despite the widespread atmospheric presence of mineral dust and clay aerosol, there is still much uncertainty associated with their contribution to climate forcing especially as related to their nonspherical shape and rough surface. This paper provides a method for retrieving effective refractive indices for a series of clay aerosols produced via dry-generation, which more closely captures natural emission mechanisms. Aerosols were generated using a wrist-action shaker, size determined via tandem differential mobility analysis and optically interrogated with a cavity ring-down spectrometer. The three specific aerosols studied are montmorillonite, Na-rich montmorillonite, and illite. The retrieved refractive indices at 532 nm, room temperature, and <2% relative humidity are m = 1.55­(3) + 0.15(6)i, m = 1.60(2) + 0.00(4)i, and m = 1.27(4) + 0.31(7)i, respectively. The effective and bulk refractive index values were then used to calculate single scattering albedo, which shows the changed warming potential of montmorillonite and illite based on effective values. These results may be used to refine the inclusion of dust components in climate models.