Refractive indices of various H2SO4–H2O, HNO3–H2O, and H2SO4–HNO3–H2O solutions were measured at four wavelengths in the visible (351.0, 533.5, 632.9, and 782.6 nm) over a temperature range from 30 to -60 °C. The temperature dependence has been determined for the first time to the authors’ knowledge. This dependence is of importance for applications to atmospheric aerosols at low temperatures. In particular, it is shown that (1) the molar refractivity of the solutions is independent of temperature, whereas the temperature dependence of the refractive index arises solely through the temperature dependence of the solution’s mass density, (2) the molar refractivities of H2SO4 and HNO3 in a ternary solution may be calculated as the weighted sum of the molar refractivities of two binary solutions evaluated at a concentration that corresponds to the total acid concentration, and (3) the H2O molar refractivity in the solutions may be taken equal to that of pure water. Although the data for the ternary system have been used for this model verification, data for binary H2SO4–H2O and HNO3–H2O solutions were used to improve the accuracy of the modeled refractive indices to better than 0.0017% or 0.15% for concentrations of 5–70 wt. % and wavelengths from the near ultraviolet to the near infrared (0.25–2 µm).
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