Direct detection of atmospheric atomic bromine leading to mercury and ozone depletion

Abstract

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. However, 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. Measured bromine atom levels reached 14 parts per trillion (ppt, pmol mol−1; 4.2 × 108 atoms per cm−3) and were up to 3–10 times 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 provides a breakthrough in quantitatively constraining bromine chemistry in the polar atmosphere, where this chemistry connects the rapidly changing surface to pollutant fate.

Pan-Arctic surface ozone: modelling vs measurements

“…Although our models are not able to reproduce ODEs at all spatial scales, the success of the models in capturing ODEs and BEEs (e.g., at a spatial scale >~500 km) gives additional evidence for the proposed mechanism of SSA production (as well as acting as a source of bromine) from blowing snow on sea ice (Yang et al, 2008;. Therefore, we 30 may predict that changes in sea ice extent and type in a warming climate will influence Arctic boundary layer chemistry and Arctic climate, including the deposition of atmospheric mercury to the surface (Wang et al, 2019).…”

Evaluating the impact of blowing snow sea salt aerosol on springtime BrO and O<sub>3</sub> in the Arctic

“…stable Arctic boundary layer is decoupled from convective exchange with the free troposphere (Moore et al, 2014;Seabrook et al, 2011;Wang et al, 2019). Furthermore as boundary layer O3 reaches very low levels (<4 ppbv), BrO production via R3 530 is suppressed and atomic Br becomes much more abundant than BrO (Neuman et al, 2010;Wang et al, 2019), such that satellites would not necessarily observe co-located O3 depletion and enhanced BrO VCDtropo.…”

“…convective exchange with the free troposphere (Custard et al, 2017;Peterson et al, 2015Peterson et al, , 2017Pratt et al, 2013;Wang et al, 2019). Fig.…”

Long-Term Observations of Atmospheric Speciated Mercury at a Coastal Site in the Northern Gulf of Mexico during 2007–2018

“…In polar regions, GEM can be quickly oxidized by reactive bromine species and its concentration reduction are well correlated with enhanced GOM concentrations [47][48][49][50]. However, during the GEM depletion events that were observed at the Grand Bay site, GOM and PBM concentrations were very low, with a mean concentration of 0.6 pg m −3 for GOM and of 3.4 pg m −3 for PBM ( Figure 13).…”

“…During this event, standard additions of GEM were conducted and the recovery of the GEM standard additions at the inlet on the tower remained relatively constant, which indicated that the observed GEM depletion was not a measurement artifact and it was not due to any potential losses of GEM in the ambient air through the sampling system. In polar regions, GEM can be quickly oxidized by reactive bromine species and its concentration reduction are well correlated with enhanced GOM concentrations [47][48][49][50]. However, during the GEM depletion events that were observed at the Grand Bay site, GOM and PBM concentrations were very low, with a mean concentration of 0.6 pg m −3 for GOM and of 3.4 pg m −3 for PBM ( Figure 13).…”