Direct Detection of Atmospheric Atomic Bromine Leading to Mercury and Ozone Depletion

Bromine atoms play a central role in atmospheric reactive halogen chemistry, depleting ozone and elemental mercury, thereby enhancing deposition of toxic mercury, particularly in the Arctic near-surface troposphere. Yet, direct bromine atom measurements have been missing to date, due to the lack of analytical capability with sufficient sensitivity for ambient measurements. Here we present direct atmospheric bromine atom measurements, conducted in the springtime Arctic near Utqiagvik, Alaska in March 2012. Measured bromine atom levels reached up to 14 ppt (4.2×10⁸ atoms cm^-3) and were up to 3-10 higher than estimates using previous indirect measurements not considering the critical role of molecular bromine. Observed ozone and elemental mercury depletion rates are quantitatively explained by the measured bromine atoms, providing field validation of highly uncertain mercury chemistry. Following complete ozone depletion, elevated bromine concentrations are sustained by photochemical snowpack emissions of molecular bromine and nitrogen oxides, resulting in continued atmospheric mercury depletion. This study shows that measured bromine atoms, resulting from photochemical snowpack production of molecular bromine, can quantitatively explain ozone and mercury loss in the near-surface polar atmosphere.