Determination of the refractive index of insoluble organic extracts from atmospheric aerosol over the visible wavelength range using optical tweezers

Optical tweezers were combined with Mie spectroscopy to determine the real refractive index of insoluble organic material extracted from atmospheric aerosols over a wide wavelength interval. The real refractive index of the extracts followed a Cauchy equation between 460-700 nm for organic aerosol extracts collected from urban (London), remote (Antarctica) and wood burning environments. The refractive index values compare well with previous monochromatic or very small wavelength range measurements of refractive index. In addition, the real refractive index values were used in a one-dimensional radiative-transfer calculation of the top-of-the atmosphere albedo comprising of an atmosphere containing a 3 km thick layer of aerosol comprising either pure water, insoluble organic aerosol, or aqueous core-organic shell aerosol.