Laboratory study of the interaction of HO2 radicals with the NaCl, NaBr, MgCl2·6H2O and sea salt surfaces

Abstract

The uptake of HO₂ radicals on synthetic sea salt, NaCl, NaBr and MgCl₂·6H₂O 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 × 10⁻⁹ exp[(3990 ± 200)/T], 2.2 × 10⁻⁸ exp[(3340 ± 180)/T], 1.2 × 10⁻⁸ exp[(3570 ± 180)/T] and 3.8 × 10⁻⁵ exp[(1710 ± 60)/T] on sea salt, NaCl, NaBr and MgCl₂·6H₂O, respectively (quoted uncertainty is 2σ 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.