A quantitative test of infrared optical constants for supercooled sulphuric and nitric acid droplet aerosols

[摘要] In situ Fourier transform infrared (FTIR) extinction spectra of supercooledH₂SO₄/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 fora range of aerosol compositions and at temperatures extending down to 192K. The measured spectra were quantitatively analysed in terms of aerosol composition and mass concentrationby using Mie theory in combination with published refractive index data as input parameters.Simultaneously, total sulphuric acid and nitric acid mass concentrations from filter analysisand total water concentrations measured with the Lyman-a hygrometer of ForschungszentrumJülich were used to calculate the aerosol composition at thermodynamic equilibrium insidethe aerosol chamber. By comparing these measured aerosol parameters with those retrievedfrom the analysis of the FTIR spectra, the accuracy of the literature data sets of refractiveindices could be assessed. In summary, four data sets were tested in the H₂SO₄/H₂O system aswell as two data sets in the HNO₃/H₂O system, partly revealing significant discrepancies inthe retrieved aerosol properties. Potential explanations for these differences are discussed inthis paper.

[学科分类] 大气科学