THERMODYNAMICS AND KINETICS OF THE SOLID-SOLUTION OF HNO3 IN ICE

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 degrees C. The diffusion coefficient of HNO3, follows the Arrheni us expression D = 1.37 x 10(-2610/T) cm(2) s(-1), but these values pro bably represent upper limits because of the existence of diffusion sho rt circuits. The solubility of HNO3 in ice, X-HNO3(0), is about 5 x 10 (-7) mole fraction at -15 degrees C and P-HNO3 = 10(-3) Pa, and its te mperature and partial pressure dependences are X-HNO3(0) = 2.37 x 10(- 12) e((3532.2/T))(P-HNO3)(1/2.3) mole fraction, where PHNO3 is the HNO 3 partial pressure in Pa, and T is the temperature in Kelvin. These so lubility data have been used to build the partial pressure versus inve rse temperature phase diagram and to calculate the solidus of the temp erature-composition phase diagram and the ice-to-water partition coeff icient K. K varies with temperature between 3 x 10(-6) and 1.6 x 10(-5 ) Implications for ice cloud chemistry and for the interpretation of i ce core analyses are briefly discussed.