Interaction of Nitrous Acid with Polycrystalline Ice: Adsorption on the Surface and Diffusion into the Bulk

The thermodynamic and kinetic constants needed to model the interactions of nitrous acid (HONO) with ice were measured. The experiments were done in a packed ice bed flow tube at temperatures between 213 and 253 K and at HONO gas phase concentrations between 0.4 and 137 ppbv. The experiments were performed using radioactively labeled HO13NO molecules. The use of the short-lived isotope 13N (t1/2 ≈ 10 min) enabled in situ monitoring of the migration of HO13NO in the flow tube. The measurements showed that the interactions do not only occur through adsorption but also via diffusion into polycrystalline ice. A method is suggested to disentangle the bulk and the surface processes. Using this method, the temperature dependence of the linear partition coefficient was found to be Klin,C,HONO = 7.4 × 10−11 exp(5.4 × 103/T) in units of m. The enthalpy and entropy of adsorption of HONO on ice were ΔHads,HONO = −45(±20) kJ mol−1 and ΔSads,HONO0 = −17(±89) J mol−1 K−1, respectively for the standard conditions Astd/Vs...