Chemical transformation of bromine chloride at the air/water interface

The uptake of gaseous bromine chloride (BrCl) on aqueous surfaces was measured, as a function of temperature and liquid composition, using the droplet train technique coupled to a mass spectrometer. The uptake rate on pure water was too slow to be directly measured (i.e., gamma < 10(-3)). In order to increase the uptake kinetics above the detection limit of the experimental set-up, NaBr, NaI and NaOH were used as scavengers. The uptake kinetics on sodium bromide solutions were complicated by the interference of Cl-2 and Br-2 which are in equilibrium with gaseous BrCl. Therefore, we report results on the other two scavengers. On sodium hydroxide solutions, the uptake is driven by the bulk reactivity of BrCI toward OH-yielding an average value of the mass accommodation coefficients alpha of 0.33 +/- 0.18 in the temperature range from 270-285 K. On sodium iodide solutions, the uptake kinetics were again driven by the bulk reactivity of the in-coming bromine chloride but, in addition a surface reaction channel was found. (C) 2001 Elsevier Science Ltd. All rights reserved.