A temperature- and composition-dependent study of H2SO4 aerosol optical constants using Fourier transform and tunable diode laser infrared spectroscopy

Frequency-dependent optical constants have been determined from the Fourier transform infrared spectra of laboratory-generated liquid sulfuric acid/wa ter aerosols over a range of temperatures and compositions that are relevan t to the upper troposphere and lower stratosphere of Earth. The composition s of the particles were determined in situ using a tunable diode laser to m onitor equilibrium water vapor pressures, The infrared complex refractive i ndices of sulfuric acid are shown to be strongly dependent on temperature a nd composition, because of changes in the equilibrium between sulfate and b isulfate ions. Results from this study also have implications in understand ing: the temperature dependence of intermolecular interactions within ionic solutions. The database presented here is the most extensive yet available for the liquid solutions of sulfuric acid.