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Black Carbon Ageing in the CCCma AGCM

Black Carbon Ageing in the CCCma AGCM. Betty Croft and Ulrike Lohmann * Department of Physics and Atmospheric Science Dalhousie University, Halifax, N.S. Canada

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Black Carbon Ageing in the CCCma AGCM

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  1. Black Carbon Ageing in the CCCma AGCM Betty Croft and Ulrike Lohmann* Department of Physics and Atmospheric Science Dalhousie University, Halifax, N.S. Canada *: now at ETH Zurich, Zurich, Switzerland Knut von Salzen Canadian Centre for Climate Modelling and Analysis University of Victoria, Victoria, B.C. Canada

  2. Outline • Introduction • BC ageing schemes • CCCma GCM burdens, concentrations and lifetimes • Comparison with surface layer observations • Conclusions

  3. Climate Effects of Carbon Aerosol

  4. CCCma AGCM15b overview • 3 year model simulations using T47 horizontal resolution (3.75° x 3.75°). • 35 vertical hybrid p-σ levels to 50 hPa. • Prognostic variables include T, qv, ln(ps), vorticity, divergence, liquid and ice water content.

  5. BC treatment in CCCma GCM Primary Emissions 80% 20% λ=24h Insoluble BC Soluble/Mixed BC Deposition Deposition Transport Transport

  6. BC Emissions • Fossil fuel: 3.04 Tg C/yr • Bio-fuel: 1.64 Tg C/yr (Bond et al. 2004) • Open burning: 3.04 Tg C/yr (van der Werf et al. 2003)

  7. BC emissions (kg C/m2/s)

  8. BC Burden – fixed 24h halflife

  9. 24h Halflife vs. No Ageing Global and annual mean: 0.14 Tg C vs. 2.15 Tg C

  10. Physical Processes related to ageing Condensation Coagulation Aerosols H2SO4 HNO3 OH O3 Oxidation

  11. BC ageing schemes Fixed 24h half life - exponential decay - Lohmann et al. (1999) - Pöschl et al. (2002), Tsigaridis & Kanakidou (2003) - ozone and water vapour compete. • - Riemer et al. (2004) - Day: fixed e-folding time (2h) - Night: use aerosol number concentration Oxidation Condensation/coagulation

  12. BC burdens (mg C/m2)

  13. BC concentrations (ng C/m3)

  14. Percent BC in soluble/mixed state

  15. BC global and annual means

  16. red *: obs black-o-: FIX-LIFE green*: COND-COAG-OXID black*: OXID blue -o-: NO-AGEING

  17. red *: obs black-o-: FIX-LIFE green*: COND-COAG-OXID black*: OXID blue -o-: NO-AGEING

  18. red *:obs black-o-: FIX-LIFE green*: COND-COAG-OXID black*: OXID blue -o-: NO-AGEING

  19. Model to observation comparison

  20. Conclusions • Using year 2000 emissions (8.0 Tg C/yr), the global BC burden is found to be about 0.11 Tg C. • Reasonable BC burdens can be predicted with a coagulation/condensation/oxidation parameterization. • A physically based BC aging treatment allows the BC life to respond to regional conditions in a GCM. • The global BC burden and ultimately the climate forcing is sensitive to the BC ageing parameterization in a global climate model.

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