Real-time kinetics of the uptake of HOBr and BrONO2 on ice and in the presence of HCl in the temperature range 190-200 K

The uptake kinetics of the title compounds on ice with and without HCl has been measured in a Teflon-coated low-pressure flow reactor (Knudsen cell) at temperatures of 190-200 K. At 190 K, values of the uptake coefficient for BrONO2 are of the order of 0.25 +/- 0.09 at limiting low doses and low flow rates of 10(14) molecules per pulse and 10(14) molecules s(-1), respectively. The reaction leads to the formation of HOBr and also to the secondary product Br2O resulting from the reaction between BrONO2 and HOBr. The reaction of BrONO2 on HCl-doped ice was studied under pulsed and continuous flow conditions. It appears that the formation of both BrCl and HOBr occurs promptly. In contrast to CIONO2 on ice, the reaction of BrONO2 with H2O does not involve the formation of a precursor releasing hypobromous acid. HOBr itself is found to interact with ice: at 190 and 200 K, values of the uptake coefficient are 0.27 +/- 0.04 and 0.15 +/- 0.01 at a residence time of 0.3 s, respectively. These values are higher than the ones previously published. The rate of interaction of HOBr on HCl-doped ice is enhanced with respect to the one on pure ice, and BrCl is observed as a product. Possible atmospheric implications of this work are discussed.