Hydrolysis of N 2 O 5 and ClONO 2 on the H 2 SO 4 /HNO 3 /H 2 O ternary solutions under stratospheric conditions

The reaction probabilities of N 2 O 5 and ClONO 2 with H 2 O on liquid sulfuric acid surfaces have been reexamined to determine the effect of HNO 3 on these two hydrolysis rates, using a fast flow reactor coupled to a chemical ionization mass spectrometer. The measurements were carried out by maintaining constant H 2 O and HNO 3 partial pressures and by varying temperatures between 227 and 195 K in order to mimic compositions representative of stratospheric aerosols. For experiments excluding HNO 3 , the reaction probability of N 2 O 5 hydrolysis was found to be near 0.1, independent of temperature and H 2 SO 4 content. This is in agreement with results previously measured under similar conditions. In the presence of gaseous HNO 3 at stratospheric concentrations, the reaction probability was observed to decrease from about 0.09 at 218 K to about 0.02–0.03 at 195 K for P H2O = 3.8 × 10 −4 −1.0 × 10 −3 Torr, showing that incorporation of HNO 3 into liquid sulfuric acid greatly retarded the N 2 O 5 hydrolysis. The ClONO 2 reaction with H 2 O on liquid sulfuric acid, on the other hand, did not appear to be affected by the presence of HNO 3 .