Heterogeneous interconversion reactions of BrNO2, ClNO2, Br2, and Cl2

The heterogeneous reactions leading to formation and loss of BrNO2 on salt solutions as a model substrate for atmospheric sea salt aerosol are investigated. Further to the reaction of ClNO2 with bromide solutions, the reaction of Br-2 with nitrite solution was found to be a convenient method for the synthesis of BrNO2. We measured the temperature-dependent lifetime of BrNO2 in a quartz cell and obtained the activation energy E-A = 89 +/- 9 kJ/mol for the unimolecular decay at atmospheric pressure. The reactive uptake of BrNO2 and ClNO2 on water and aqueous solutions was determined using a wetted-wall flow tube technique. We observed the reactions Br-2 + NO2- <----> BrNO2 + Br-, Cl-2 + NO2- --> ClNO2 + Cl-, and the net reaction ClNO2 + Br- <----> BrNO2 + Cl-. BrNO2 and ClNO2 both react with NO2- to release NO2 into the gas phase. Observed concentration profiles in the gas phase and in solution can be described qualitatively by a numerical model of the diffusion and reaction processes in the-experimental setup.