Reactive Uptake of ClNO2on Aqueous Bromide Solutions

The reactive uptake of ClNO 2 on pure water, NaBr, and mixed NaBr/NaCl solutions was studied using a wetted wall flow tube equipped with a quadrupole mass spectrometer. The measured uptake coefficient, γ expt, varied between approximately 1 × 10 -5 and 1 × 10 -4, depending on the aqueous salt concentration. Parameters governing the reactive uptake on NaBr solutions were determined interdependently as H 2 D 1 = (0.101 ± 0.015) M cm 2 atm -2 s -2 . The accommodation coefficient, α, for ClNO 2 on aqueous solutions at 275 K was found to be (9 ± 4) × 10 -3 . The major gas-phase products of the uptake and reaction of ClNO 2 and Br - were found to be Br 2 and BrNO 2 . BrNO 2 is formed initially and is converted to Br 2 in a secondary reaction with Br - in the aqueous phase. BrCl is a minor product. The presence of 1M Cl - had no effect on either the kinetics of uptake or the products formed. By exchanging the halide solutions for 0.1 M OH -, the uptake rate could be increased so that the diffusion limit was reached in the reactor. Variation of the pressure yielded the diffusion coefficients of ClNO 2 in He and N 2 as 275 ± 26 and 75 ± 6 Torr cm 2 s -1, respectively. The implications of these results for the halogen chemistry of the marine boundary layer are discussed.