The relative importance of chlorine and bromine radicals in the oxidation of atmospheric mercury at Barrow, Alaska

Gaseous elemental mercury (GEM) is relatively long lived in the midlatitudes and can be transported long distances in the atmosphere. In the Polar Regions, mercury can have a much shorter lifetime and is known to experience episodic depletions following polar sunrise in concert with ozone depletion events.

A series of photochemically initiated reactions involving halogen radicals is believed to be the primary pathway responsible for converting elemental mercury to oxidized forms of reactive gaseous mercury (RGM) that are subsequently deposited to snow and ice surfaces. Using field measurements from the Ocean-Atmosphere-Sea Ice-Snowpack (OASIS) 2009 field campaign of GEM, RGM, ozone, and a large suite of both inorganic halogen and volatile organic compounds, we calculated steady state Br and Cl atom concentrations and investigated the contribution of Br, BrO, Cl, ClO, O₃, and OH to the observed decay of GEM for five cases of apparent first-order decay.