Absorption Spectra and Optical Constants of Binary and Ternary Solutions of H₂SO₄, HNO₃, and H₂O in the Mid Infrared at Atmospheric Temperatures

Abstract

Fourier transform infrared transmission (FTIR) measurements of thin films of aqueous sulfuric and nitric acid and their ternary mixture were performed over a wide range of composition and temperature. On the basis of a systematic study of the spectra a database of optical constants for sulfuric acid (c ≤ 80 wt %) and nitric acid (c ≤ 50 wt %) for temperatures 183 ≤ T ≤ 293 K were obtained. A mixing rule is presented to calculate k(ν̄) and n(ν̄) spectra for H2SO4/HNO3/H2O solutions and validated against the new FTIR measurements of ternary solutions. This covers optical constants in the entire range of atmospheric relevance and is easily accessible for various applications, e.g., satellite aerosol observations.