Reaction of ClONO₂with H₂O and HCl in Sulfuric Acid and HNO₃/H₂SO₄/H₂O Mixtures

Measurements of the reaction probabilities (γ) for ClONO 2 onto sulfuric acid solutions at 200−270 K are described. ClONO 2 uptake due to reaction with H 2 O and with HCl in H 2 SO 4 solutions (45−55 wt %) was investigated at 203−205 K. ClONO 2 hydrolysis was also investigated on 36.5, 40, and 75 wt % sulfuric acid solutions over a range of temperatures. The measured γ are generally in good agreement with previously reported values. In addition, the solubility of HCl was determined for 45 and 50 wt % sulfuric acid from 200 to 225 K. The uptake of ClONO 2 onto small sulfuric acid particles was studied resulting in a lower limit to the sticking coefficient of 0.5. ClONO 2 reaction probabilities were also measured on H 2 SO 4 solutions containing significant amounts of HNO 3 . In opposition to previous reports, HNO 3 was found to have a significant effect on γ for ClONO 2: it is as low as one-half of that expected for the comparable HNO 3 -free solutions. The measured γ on sulfuric acid solutions at 203 ± 2 K are discussed in terms of solubility, diffusivity, and bulk and surface reactions. Within this framework, the measured γ were fit as a function of H 2 SO 4 and HCl content, thus allowing for the measurements to be extrapolated to atmospheric conditions.