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

Study on Correlation between Tropospheric Bromine Monoxide Level and First-year Sea Ice. Sungyeon Choi. Introduction. Bromine Monoxide(BrO) Highly correlated with Ozone Depletion Event in polar boundary layer in springtime(Evans et al, 2003) HOBr + Br- + H+ -> H2O + Br2 Br2 + hv -> 2Br

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

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  1. Study on Correlation between Tropospheric Bromine Monoxide Level and First-year Sea Ice Sungyeon Choi Spring 2008

  2. Introduction • Bromine Monoxide(BrO) • Highly correlated with Ozone Depletion Event in polar boundary layer in springtime(Evans et al, 2003) HOBr + Br- + H+ -> H2O + Br2 Br2 + hv -> 2Br Br + O3 -> BrO + O2 BrO + HO2 -> HOBr + O2 _________________________________________ Net: H+ + Br- + HO2 + O3 -> Br + H2O + 2O2 Spring 2008

  3. Motivation • 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 Spring 2008

  4. Model 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 Spring 2008

  5. Model 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 Spring 2008

  6. Model 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. Spring 2008

  7. GOME BrO Measurement • Measures solar backscatter spectra to obtain atmospheric BrO column amount (240-790nm) • Spatial resolution of 320 km * 40 km K. Chance, 1998 Spring 2008

  8. GOME BrO Measurement Spring 2008

  9. SeaWind 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 Spring 2008

  10. SeaWind Backscatter Map Spring 2008

  11. Results - Spatial Correlation • Spatial Correlation between monthly averaged tropospheric BrO level and FYI fraction • Does not show a big correlation Spring 2008

  12. Results - Model Running Lifetime: 4h 4ppt/4h Spring 2008

  13. Results - Model Running Lifetime: 36h 1ppt/6h Spring 2008

  14. Discussion • 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 Spring 2008

  15. Reference • 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 Spring 2008

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