Laboratory measurements of the optical properties of sea salt aerosol R. Irshad1, R. G. Grainger1, D. M. Peters1, R. A. McPheat2, K. M. Smith2, and G. Thomas1 1Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, University of Oxford, UK 2Space Science and Technology Department, Rutherford Appleton Laboratory, Didcot, UK
Abstract. The extinction spectra of laboratory generated sea salt aerosols have been
measured from 1 μm to 20 μm using a Bruker 66v/S FTIR spectrometer.
Concomitant measurements include temperature, pressure, relative humidity and
the aerosol size distribution. The refractive indices of the sea salt aerosol
have been determined using a simple harmonic oscillator band model
(Thomas et al., 2004) for aerosol with relative humidities at eight different values
between 0.4% to 86%. The resulting refractive index spectra show
significant discrepancies when compared to existing sea salt refractive
indices calculated using volume mixing rules (Shettle
and Fenn, 1979). Specifically, an
additional band is found in the refractive indices of dry sea salt aerosol
and the new data shows increased values of refractive index at almost all
wavelengths. This implies that the volume mixing rules, currently used to
calculate the refractive indices of wet sea salt aerosols, are inadequate.
Furthermore, the existing data for the real and imaginary parts of the
refractive indices of dry sea salt aerosol are found not to display the
Kramers-Kronig relationship. This implies that the original data used for the
volume mixing calculations is also inaccurate.
Citation: Irshad, R., Grainger, R. G., Peters, D. M., McPheat, R. A., Smith, K. M., and Thomas, G.: Laboratory measurements of the optical properties of sea salt aerosol, Atmos. Chem. Phys., 9, 221-230, doi:10.5194/acp-9-221-2009, 2009.