Production mechanisms of molecular Cl2, Br2, and I2 from the multiphase oxidation of halide-ice surfaces

The release of molecular halogens (particularly Cl2, Br2, and I2) into the Arctic boundary layer can cause the rapid and episodic depletion of surface-level ozone, thus altering the oxidation capacity of the atmosphere. These halogens have long been believed to primarily originate from frozen, saline surfaces, and direct production has been recently observed in situ. However, the oxidation mechanisms responsible for this halogen production remain unclear. Here, we present results from a series of laboratory experiments in which gas-phase Cl2, Br2, and I2 production was observed from the multiphase oxidation of frozen, simulated seawater solutions. For this study, we employed a coated-wall flow tube coupled to a chemical ionization mass spectrometer, and tested the effects of varying the solution pH and halogen oxidant (including O3, NO2-, N2O5, and HOOH).