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Halogen chemistry in Eureka: What are the sources of reactive bromine?

Bromine explosions and corresponding ozone depletion events are common in the Arctic spring. The sources of reactive bromine include the snowpack and aerosols, but the exact conditions and mechanisms required for bromine release are not well understood. Here we present a four-year time series of springtime BrO columns at Eureka, Nunavut. We find that wind direction controls the types of BrO events we observe. Winds from the north bring air from the Arctic Ocean, and snow on all sea ice (as opposed to snow on first-year ice only) is likely the source of the observed BrO. Winds from the southeast, on the other hand, often correspond to storms, and aerosols play an important role in maintaining high BrO during these events. We find that, contrary to previous studies, wind speed and atmospheric stability have a limited influence on BrO, due to the elevation of the measurement site. We show that high coarse mode aerosol concentrations are necessary and sufficient for the presence of high BrO columns in Eureka, and argue that these aerosols are an important source of reactive bromine in the Arctic.