Laboratory measurements of the optical properties of sea salt aerosol

摘要

The extinction spectra of laboratory generated sea salt aerosols have beenmeasured from 1 μm to 20 μm using a Bruker 66v/S FTIR spectrometer.Concomitant measurements include temperature, pressure, relative humidity andthe aerosol size distribution. The refractive indices of the sea salt aerosolhave been determined using a simple harmonic oscillator band model(Thomas et al., 2004) for aerosol with relative humidities at eight different valuesbetween 0.4% to 86%. The resulting refractive index spectra showsignificant discrepancies when compared to existing sea salt refractiveindices calculated using volume mixing rules (Shettleand Fenn, 1979). Specifically, anadditional band is found in the refractive indices of dry sea salt aerosoland the new data shows increased values of refractive index at almost allwavelengths. This implies that the volume mixing rules, currently used tocalculate the refractive indices of wet sea salt aerosols, are inadequate.Furthermore, the existing data for the real and imaginary parts of therefractive indices of dry sea salt aerosol are found not to display theKramers-Kronig relationship. This implies that the original data used for thevolume mixing calculations is also inaccurate.