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).