Molecular Halogens Above the Arctic Snowpack: Emissions, Diurnal Variations, and Recycling Mechanisms

Elevated levels of reactive bromine and chlorine species in the springtime Arctic boundary layer contribute to ozone depletion and mercury oxidation, as well as reactions with volatile organic compounds. Recent laboratory and field studies have revealed that snowpack photochemistry leads to Br-2 and Cl-2 production, the mechanisms of which remain poorly understood. In this work, we use a photochemical box model, with a simplified snow module, to examine the halogen chemistry occurring during the March 2012 Bromine, Ozone, and Mercury Experiment (BROMEX) near Utqiagvik (Barrow), Alaska. Elevated daytime Br-2 levels (e.g., 6-30 parts per trillion (ppt) at around local noon) reported in previous studies and in this work may be explained by Br + BrNO2/BrONO2 reactions under conditions of depleted O-3 (