Kinetic model for reaction of ClONO2 with H2O and HCl and HOCl with HCl insulfuric acid solutions

The heterogeneous reactions ClONO2 + H2O --> HOCl + HNO3 (1), ClONO2 + HCl --> Cl-2 + HNO3 (2), and HOCl + HCl + Cl-2 + H2O (3) on stratospheric aeros ols convert ClONO2 and HCl to photo-labile species, producing reactive CI a nd CIO which are responsible for catalyzing ozone destruction in the lower stratosphere. The extent of the resulting ozone loss mirrors the steep nega tive temperature dependence of these reactions, which strongly depend on th e solubility of ClONO2, HCl, and HOCl, and on the activity of H2O. Predicti ng the effect of these heterogeneous processes throughout the stratosphere requires detailed modeling of liquid phase solubility, diffusion, and react ion kinetics. A series of recent experiments from a number of laboratories have refined measurements of liquid diffusion coefficients, HCl and HOCl so lubilities, and the reactivity of ClONO2 + H2O, ClONO2 + HCl and HCl + HOCl on liquid films, droplets, and aerosols. On the basis of those measurement s we present a phenomenological uptake model in which parameterizations of ClONO2, HCl, and HOCl heterogeneous kinetics appropriate for stratospheric H2SO4/H2O aerosols are addressed. In this model we suggest that under high acid concentration conditions both HOCl and ClONO2 are protonated before th ey react with HCl. Data for all three reactions in concentrated H2SO4 solut ion indicate an acid-catalyzed reaction channel, which had previously been inferred for ClONO2 hydrolysis. This updated parameterization is most signi ficant at relatively high temperatures above 205 K which produce H2SO4 aero sols of > 60 acid wt%, where the acid-catalyzed reaction channels dominate. The comparisons between our new formulation and other recent formulations are presented.