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

The heterogeneous interactions of ClONO₂, HCl and HNO₃ 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% H₂SO₄ solutions at temperatures in the range -63 to -43°C. Heterogeneous loss, but not reaction, of HNO₃ 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 HNO₃. ClONO₂ also reacted with HCl dissolved in the 65% H₂SO₄ solution at -63°C, forming gaseous Cl₂. In all cases studied, the sticking and/or reaction coefficients were much larger for the 65% H₂SO₄ solution at -63°C than for the 75% solution at -43°C.