Study on Correlation between Tropospheric Bromine Monoxide Level and First-year Sea Ice

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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

€

∂[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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GOME BrO MeasurementGOME BrO Measurement

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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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SeaWind Backscatter MapSeaWind Backscatter Map

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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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Results - Model RunningResults - Model Running

Lifetime: 4h

4ppt/4h

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Results - Model RunningResults - Model Running

Lifetime: 36h

1ppt/6h

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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