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Title: Sulfate production by reactive bromine: Implications for the global sulfur and reactive bromine budgets: Sulfur-Halogen Interactions
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Journal Name:
Geophysical Research Letters
Medium: X
Sponsoring Org:
National Science Foundation
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  1. Abstract

    Snowpack emissions are recognized as an important source of gas‐phase reactive bromine in the Arctic and are necessary to explain ozone depletion events in spring caused by the catalytic destruction of ozone by halogen radicals. Quantifying bromine emissions from snowpack is essential for interpretation of ice‐core bromine. We present ice‐core bromine records since the pre‐industrial (1750 CE) from six Arctic locations and examine potential post‐depositional loss of snowpack bromine using a global chemical transport model. Trend analysis of the ice‐core records shows that only the high‐latitude coastal Akademii Nauk (AN) ice core from the Russian Arctic preserves significant trends since pre‐industrial times that are consistent with trends in sea ice extent and anthropogenic emissions from source regions. Model simulations suggest that recycling of reactive bromine on the snow skin layer (top 1 mm) results in 9–17% loss of deposited bromine across all six ice‐core locations. Reactive bromine production from below the snow skin layer and within the snow photic zone is potentially more important, but the magnitude of this source is uncertain. Model simulations suggest that the AN core is most likely to preserve an atmospheric signal compared to five Greenland ice cores due to its high latitude location combined with a relatively high snow accumulation rate. Understanding the sources and amount of photochemically reactive snow bromide in the snow photic zone throughout the sunlit period in the high Arctic is essential for interpreting ice‐core bromine, and warrants further lab studies and field observations at inland locations.

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  2. Abstract

    Tropospheric bromine radicals in the Arctic efficiently remove ambient ozone and oxidize gaseous elemental mercury. Ground‐based bromine monoxide (BrO) observations from the Arctic Ocean and Utqiaġvik (formerly Barrow) are combined with Modern Era Retrospective Analysis for Research and Applications version 2 reanalysis meteorological fields to determine how BrO varies with environmental conditions. The mean seasonal BrO abundance varies from year to year (p < 0.001), while regional variance in mean BrO is not statistically significant (p > 0.11). Principal component analysis derived three important principal components from the environmental data set. The third principal component explains the most variance in BrO and is correlated with low ozone and cold temperatures. This principal component is consistent with high BrO during ozone depletion events at cold temperatures and can work concurrently with each of the other two principal components to generate two distinct environmental types of high BrO events. The first principal component consists of a less‐stable, thick, mixed layer and low atmospheric pressure and is consistent with observations of high BrO in low‐pressure systems (e.g., storms). The second principal component consists of cold and stable conditions and is consistent with high BrO under surface‐based temperature inversions. Our principal component regression model predicted the both the vertical column density of BrO in the lowest 2 km of the troposphere (R = 0.45) and the vertical column density of BrO in the lowest 200 m (R = 0.54). This statistical description of two types of reactive bromine events may help to harmonize space‐based and ground‐based observations.

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