Experimental study on the release of Cl₂ from NaCl upon OH radical uptake

An experimental study using a bead-filled flow tube system coupled to a high-pressure chemical ionization mass spectrometer was performed to characterize the products and kinetic mechanism of the release of chlorine containing species by the heterogeneous reaction of OH radicals on a NaCl surface. Although only species corresponding to HCl were observed, the kinetic model and an experiment with O₃ verified that Cl₂, the sole product of the heterogeneous reaction, was converted to HCl in the presence of H. The yield of Cl₂ per OH was determined to be 0.020±0.002 and 0.022±0.002 at 0 and 6% of relative humidity (RH), respectively. The XPS study indicated that the chlorine deficit caused by OH uptake was enhanced under wet conditions. An enhancement in Cl₂ production was observed under wet conditions, which was consistent with the measured chlorine deficit in NaCl. Two reaction mechanisms were proposed to describe the heterogeneous uptake of OH by NaCl.