Laboratory study of the interaction of HO2 radicals with the NaCl, NaBr, MgCl2 center dot 6H(2)O and sea salt surfaces

The uptake of HO2 radicals on synthetic sea salt, NaCl, NaBr and MgCl2 center dot 6H(2)O dry solid films was studied over the temperature range 240 to 340 K and at 1 Torr pressure of helium using a discharge flow reactor coupled to a modulated molecular beam mass spectrometer. The Arrhenius expressions (calculated with geometric surface area) were obtained for the uptake coefficient of HO2: 3.1 x 10(-9) exp[(3990 +/- 200)/T], 2.2 x 10(-8) exp[(3340 +/- 180)/T], 1.2 x 10(-8) exp[(3570 +/- 180)/T] and 3.8 x 10(-5) exp[(1710 +/- 60)/T] on sea salt, NaCl, NaBr and MgCl2 center dot 6H(2)O, respectively (quoted uncertainty is 2 sigma statistical). H2O2 was observed as a main product of HO2 interaction with salt surface indicating a heterogeneous HO2 self reaction mechanism. The results show that the HO2 loss through heterogeneous interaction with salt surface is not sufficiently rapid to explain the observed differences between modeled and measured HO2 concentrations in remote coastal areas.