Heterogeneous interactions of chlorine nitrate, hydrogen chloride, and nitric acid with sulfuric acid surfaces at stratospheric temperatures

The heterogeneous interactions of ClONO 2 , HCl and HNO 3 with sulfuric acid surfaces were studied using a Knudsen cell flow reactor. The surfaces studied, chosen to simulate global stratospheric particulate, were composed of 65‐75% H 2 SO 4 solutions at temperatures in the range −63 to −43°C. Heterogeneous loss, but not reaction, of HNO 3 and HCl occurred on these surfaces and the measured sticking coefficients are reported. Chlorine nitrate reacted on the cold sulfuric acid surfaces, producing gas‐phase HOCl and condensed HNO 3 . ClONO 2 also reacted with HCl dissolved in the 65% H 2 SO 4 solution at −63°C, forming gaseous Cl 2 . In all cases studied, the sticking and/or reaction coefficients were much larger for the 65% H 2 SO 4 solution at −63°C than for the 75% solution at −43°C.