Thermodynamics and Kinetics of the Solid Solution of HNO₃ in Ice

Abstract

The diffusion and solubility of gaseous HNO3 in ice have been measured as a function of temperature and HNO3 partial pressure between −8 and −35 °C. The diffusion coefficient of HNO3 follows the Arrhenius expression D = 1.37 × 10-2610/T cm2 s-1, but these values probably represent upper limits because of the existence of diffusion short circuits. The solubility of HNO3 in ice, , is about 5 × 10-7 mole fraction at −15 °C and PHNO3 = 10-3 Pa, and its temperature and partial pressure dependences are = 2.37 × 10-12 e(3532.2/T)(PHNO3)1/2.3 mole fraction, where PHNO3 is the HNO3 partial pressure in Pa, and T is the temperature in Kelvin. These solubility data have been used to build the partial pressure versus inverse temperature phase diagram and to calculate the solidus of the temperature−composition phase diagram and the ice-to-water partition coefficient K. K varies with temperature between 3 × 10-6 and 1.6 × 10-5. Implications for ice cloud chemistry and for the interpretation of ice core analyses are briefly discussed.