Journal article

Analysis of reactive bromine production and ozone depletion in the Arctic boundary layer using 3-D simulations with GEM-AQ: Inference from synoptic-scale patterns

Toyota K, McConnell J, Lupu A, Neary L, McLinden C, Richter A, Kwok R, Semeniuk K, Kaminski J, Gong S, Jarosz J, Chipperfield M, Sioris C ...see all

Atmospheric Chemistry and Physics, vol. 11, issue 8 (2011) pp. 3949-3979

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Abstract

Episodes of high bromine levels and surface ozone depletion in the
springtime Arctic are simulated by an online air-quality model, GEM-AQ,
with gas-phase and heterogeneous reactions of inorganic bromine species
and a simple scheme of air-snowpack chemical interactions implemented
for this study. Snowpack on sea ice is assumed to be the only source of
bromine to the atmosphere and to be capable of converting relatively
stable bromine species to photolabile Br(2) via air-snowpack
interactions. A set of sensitivity model runs are performed for April
2001 at a horizontal resolution of approximately 100 kmx100 km in the
Arctic, to provide insights into the effects of temperature and the age
(first-year, FY, versus multi-year, MY) of sea ice on the release of
reactive bromine to the atmosphere. The model simulations capture much
of the temporal variations in surface ozone mixing ratios as observed at
stations in the high Arctic and the synoptic-scale evolution of areas
with enhanced BrO column amount ({''}BrO clouds{''}) as estimated from
satellite observations. The simulated ``BrO clouds{''} are in modestly
better agreement with the satellite measurements when the FY sea ice is
assumed to be more efficient at releasing reactive bromine to the
atmosphere than on the MY sea ice. Surface ozone data from coastal
stations used in this study are not sufficient to evaluate unambiguously
the difference between the FY sea ice and the MY sea ice as a source of
bromine. The results strongly suggest that reactive bromine is released
ubiquitously from the snow on the sea ice during the Arctic spring while
the timing and location of the bromine release are largely controlled by
meteorological factors. It appears that a rapid advection and an
enhanced turbulent diffusion associated with strong boundary-layer winds
drive transport and dispersion of ozone to the near-surface air over the
sea ice, increasing the oxidation rate of bromide (Br(-)) in the surface
snow. Also, if indeed the surface snowpack does supply most of the
reactive bromine in the Arctic boundary layer, it appears to be capable
of releasing reactive bromine at temperatures as high as -10 degrees C,
particularly on the sea ice in the central and eastern Arctic Ocean.
Dynamically-induced BrO column variability in the lower-most
stratosphere appears to interfere with the use of satellite BrO column
measurements for interpreting BrO variability in the lower troposphere
but probably not to the extent of totally obscuring ``BrO clouds{''}
that originate from the surface snow/ice source of bromine in the high
Arctic. A budget analysis of the simulated air-surface exchange of
bromine compounds suggests that a ``bromine explosion{''} occurs in the
interstitial air of the snowpack and/or is accelerated by heterogeneous
reactions on the surface of wind-blown snow in ambient air, both of
which are not represented explicitly in our simple model but could have
been approximated by a parameter adjustment for the yield of Br2 from
the trigger.

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