Reactive uptake of ClNO2 on aqueous bromide solutions

The reactive uptake of ClNO2 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, gamma(expt), varied between approximately 1 x 10(-5) and 1 x 10(-4), depending on the aqueous salt concentration. Parameters governing the reactive uptake on NaBr solutions were determined interdependently as H(2)D(1)k(Br)(II), = (0.101 +/- 0.015) M cm(2) atm(-2) s(-2). The accommodation coefficient, alpha, for ClNO2 on aqueous solutions at 275 K was found to be (9 +/- 4) x 10(-3). The major gas-phase products of the uptake and reaction of ClNO2 and Br- were found to be Br-2 and BrNO2. BrNO2 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 ClNO2 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.