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Study on Correlation between Study on Correlation between Tropospheric Bromine Monoxide Tropospheric Bromine Monoxide Level and First-year Sea IceLevel and First-year Sea Ice
Sungyeon Choi
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IntroductionIntroduction
Bromine Monoxide(BrO)– Highly correlated with Ozone Depletion Event
in polar boundary layer in springtime(Evans et al, 2003)
HOBr + Br- + H+ -> H2O + Br2Br2 + hv -> 2BrBr + O3 -> BrO + O2
BrO + HO2 -> HOBr + O2_________________________________________
Net: H+ + Br- + HO2 + O3 -> Br + H2O + 2O2
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MotivationMotivation
Salt contaminated first-year sea-ice(FYI) is suggested to be a source of reactive bromine species
Simpson et at. Investigated this hypothesis using back trajectory analysis and found FYI contact and BrO level is highly correlated [2007]
FYI fraction and trophospheric BrO at Mar 2000 are analyzed
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Model DescriptionModel Description
2D model (X, Y coordinate)Based on mass balance equation
– P ~ FYI fraction, k ~ 1/Lifetime– Including diffusion and advective transport
Domain– 106*106 grids centered at the North Pole– Resolution of 80km
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∂[BrO]
∂t= −k[BrO] + P + D∇[BrO] − v ⋅∇[BrO]
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Model DescriptionModel Description
Stability Issue– Dx = 80000 m, Dt = 3600 sec– D(Diffusion coeff.) = 100m^2/s– Average wind speed ~ 22 m/s– f = 1/2;
• [BrO]P = f([BrO0]N,[BrO0]E,[BrO]S,[BrO]W)
– Dt = 3600 s < (Dx)^2 / D = 6.4E7
Peclet number = v*Dx / D ~ 17600 – Advection dominated codition; Hybrid scheme
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Model DescriptionModel Description
Input data– Vertically averaged wind field from MM5– First-year sea ice map from Seawind
Backscatter coefficient– GOME BrO data is used as Initial BrO
distribution
Boundary condition– [BrO]_domain border = 0.
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GOME BrO MeasurementGOME BrO Measurement
Measures solar backscatter spectra to obtain atmospheric BrO column amount (240-790nm)
Spatial resolution of 320 km * 40 km
K. Chance, 1998K. Chance, 1998
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SeaWind Backscatter MapSeaWind Backscatter Map
Specialized microwave radar (scatterometer) on QuikSCAT satellite
The high backscatter values (>-10 dB) correspond to multi-year sea ice backscatter and vice versa for the First year sea ice (-12 ~ -15 dB) and open water
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Results - Spatial CorrelationResults - Spatial Correlation
Spatial Correlation between monthly averaged tropospheric BrO level and FYI fraction
Does not show a big correlation
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DiscussionDiscussion
Not very significant spatial correlation between FYI and BrO level
In model result, source term is dominant, which disagrees the observation
Another condition is needed to trigger bromine explosion observed, especially chemical mechanism
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ReferenceReference
Simpson et al., 2007, Halogens and polar boundary-layer ozone depletion, Atmos. Chem. Phys., 7, 4375-4418
Simpson et al., 2007, First-year sea-ice contact predicts bromine monoxide(BrO) levels at Barrow, Alaska better than potential frost flower contact, Atmos. Chem. Phys., 7, 621-627
Zeng et al., 2006, Simulation of Arctic O3 and NMHCS Loss, J. Geophys. Res., 11, D17313, doi:10.1029/2005JD006706