A quantitative test of infrared optical constants for supercooled sulphuric and nitric acid droplet aerosols R. Wagner1, A. Mangold2, O. Möhler1, H. Saathoff1, M. Schnaiter1, and U. Schurath1 1Forschungszentrum Karlsruhe, Institute of Meteorology and Climate Research, Karlsruhe, Germany 2Forschungszentrum Jülich, Institute of Chemistry and Dynamics of the Geosphere I (ICG-I): Stratosphere, Jülich, Germany
Abstract. In situ Fourier transform infrared (FTIR) extinction spectra of supercooled
H2SO4/H2O and HNO3/H2O solution droplets were recorded in the large coolable aerosol chamber AIDA
(Aerosol Interactions and Dynamics in the Atmosphere) of Forschungszentrum Karlsruhe for
a range of aerosol compositions and at temperatures extending down to 192
K. The measured spectra were quantitatively analysed in terms of aerosol composition and mass concentration
by using Mie theory in combination with published refractive index data as input parameters.
Simultaneously, total sulphuric acid and nitric acid mass concentrations from filter analysis
and total water concentrations measured with the Lyman-a hygrometer of Forschungszentrum
Jülich were used to calculate the aerosol composition at thermodynamic equilibrium inside
the aerosol chamber. By comparing these measured aerosol parameters with those retrieved
from the analysis of the FTIR spectra, the accuracy of the literature data sets of refractive
indices could be assessed. In summary, four data sets were tested in the H2SO4/H2O system as
well as two data sets in the HNO3/H2O system, partly revealing significant discrepancies in
the retrieved aerosol properties. Potential explanations for these differences are discussed in
Citation: Wagner, R., Mangold, A., Möhler, O., Saathoff, H., Schnaiter, M., and Schurath, U.: A quantitative test of infrared optical constants for supercooled sulphuric and nitric acid droplet aerosols, Atmos. Chem. Phys., 3, 1147-1164, doi:10.5194/acp-3-1147-2003, 2003.