Elevated concentrations of atmospheric bromine are known to cause ozone depletion in the Arctic, which is most frequently observed during springtime. We implement a detailed description of bromine and chlorine chemistry within the WRF‐Chem 4.1.1 model, and two different descriptions of Arctic bromine activation: (1) heterogeneous chemistry on surface snow on sea ice, triggered by ozone deposition to snow (Toyota et al., 2011
This content will become publicly available on January 1, 2024
- NSF-PAR ID:
- 10451538
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Date Published:
- Journal Name:
- Elem Sci Anth
- Volume:
- 11
- Issue:
- 1
- ISSN:
- 2325-1026
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract https://doi.org/10.5194/acp-11-3949-2011 ), and (2) heterogeneous reactions on sea salt aerosols emitted through the sublimation of lofted blowing snow (Yang et al., 2008,https://doi.org/10.1029/2008gl034536 ). In both mechanisms, bromine activation is sustained by heterogeneous reactions on aerosols and surface snow. Simulations for spring 2012 covering the entire Arctic reproduce frequent and widespread ozone depletion events, and comparisons with observations of ozone show that these developments significantly improve model predictions during the Arctic spring. Simulations show that ozone depletion events can be initiated by both surface snow on sea ice, or by aerosols that originate from blowing snow. On a regional scale, in spring 2012, snow on sea ice dominates halogen activation and ozone depletion at the surface. During this period, blowing snow is a major source of Arctic sea salt aerosols but only triggers a few depletion events. -
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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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Abstract. Bromine radicals influence global tropospheric chemistryby depleting ozone and by oxidizing elemental mercury and reduced sulfurspecies. Observations typically indicate a 50 % depletion of sea saltaerosol (SSA) bromide relative to seawater composition, implying that SSAdebromination could be the dominant global source of tropospheric bromine.However, it has been difficult to reconcile this large source with therelatively low bromine monoxide (BrO) mixing ratios observed in the marineboundary layer (MBL). Here we present a new mechanistic description of SSAdebromination in the GEOS-Chem global atmospheric chemistry model with adetailed representation of halogen (Cl, Br, and I) chemistry. We show thatobserved levels of SSA debromination can be reproduced in a mannerconsistent with observed BrO mixing ratios. Bromine radical sinks from theHOBr + S(IV) heterogeneous reactions and from ocean emission ofacetaldehyde are critical in moderating tropospheric BrO levels. Theresulting HBr is rapidly taken up by SSA and also deposited. Observations of SSA debromination at southern midlatitudes in summer suggest that modeluptake of HBr by SSA may be too fast. The model provides a successfulsimulation of free-tropospheric BrO in the tropics and midlatitudes in summer,where the bromine radical sink from the HOBr + S(IV) reactions iscompensated for by more efficient HOBr-driven recycling in clouds compared toprevious GEOS-Chem versions. Simulated BrO in the MBL is generally muchhigher in winter than in summer due to a combination of greater SSA emissionand slower conversion of bromine radicals to HBr. An outstanding issue inthe model is the overestimate of free-tropospheric BrO in extratropicalwinter–spring, possibly reflecting an overestimate of the HOBr∕HBr ratiounder these conditions where the dominant HOBr source is hydrolysis ofBrNO3.
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