REACTIVE UPTAKE OF CL2(G) AND BR2(G) BY AQUEOUS SURFACES AS A FUNCTION OF BR- AND I- ION CONCENTRATION - THE EFFECT OF CHEMICAL-REACTION AT THE INTERFACE

The uptake of gas-phase Cl-2 and Br-2 by aqueous NaBr and NaI solutions has been studied as a function of concentration (2.5 x 10(-4) to 0.5 M), temperature (263-293 K), and gas-liquid interaction time (2-15 ms). The uptake of O-3 by aqueous NaI solutions has also been studied for the purpose of comparison. These measurements were conducted in a droplet apparatus in which a stream of well-defined droplets (120-250 mu m in diameter) is passed through a low-pressure flow tube containing the halogen molecules. Since the solubility of the halogen molecules X(2) (X = Cl or Br) is low, the measured uptake is primarily due to the aqueous reaction of the species with the halide ion Y- (Y = Br or I) via X(2) + Y- --> XY + X(-). The magnitude of the measured halogen uptake and its functional dependence on ion concentration are not in accord with a simple bulk-phase reaction mechanism. The data indicate that reactions at the gas-liquid interface have a significant role in the gas uptake process. On the other hand, the O-3 uptake shows no evidence of interfacial reaction. The atmospheric implications of the halogen uptake results are discussed.