The kinetics of the heterogeneous reaction of BrONO2 with solid alkali halides at ambient temperature. A comparison with the interaction of ClONO2 on NaCl and KBr

The heterogeneous reactions of BrONO2 and ClONO2 with solid alkali halides have been investigated in a Teflon-coated Knudsen flow reactor at ambient temperature. The initial uptake coefficients γ0 of BrONO2 on NaCl and KBr substrates are γ0=0.31±0.12 and γ0=0.33±0.12, respectively. For NaCl substrates BrCl, Br2 and HCl and for KBr both Br2 and HBr are observed as products. HCl and HBr result from the interaction of NaCl and KBr, respectively, with HNO3 generated in the hydrolysis of BrONO2. Using NaCl we observed Br2 which is formed from heterogeneous BrONO2 decomposition which also occurs on solid KBr samples. Halogen exchange reactions are competing with hydrolysis and decomposition which also take place on non-reactive salts such as NaNO3 and Na2SO4. A high rate of initial uptake (0.2⩽γ0⩽0.4) and a Br2-yield of the order of 50% are observed on non-reactive salts with a closed mass balance for Br2. The ClONO2–salt system has been reinvestigated. Experiments on NaCl, KBr (reactive salts) and on NaNO3, Na2SO4 (non-reactive salts) have been performed. The hydrolysis of ClONO2 was not observable in contrast to heterogeneous decomposition which occurred on non-reactive salts with a Cl2-yield of (25±5)%. We fitted our uptake experiments using a simple Langmuir–Hinshelwood model with satisfactory results.