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Black Carbon Ageing in the CCCma GCM. Betty Croft and Ulrike Lohmann Department of Physics and Atmospheric Science Dalhousie University, Halifax, N.S. Canada Knut von Salzen Canadian Centre for Climate Modelling and Analysis University of Victoria, Victoria, B.C. Canada - PowerPoint PPT Presentation
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Black Carbon Ageing in the CCCma GCM
Betty Croft and Ulrike Lohmann
Department of Physics and Atmospheric Science
Dalhousie University, Halifax, N.S. Canada
Knut von Salzen
Canadian Centre for Climate Modelling and Analysis
University of Victoria, Victoria, B.C. Canada
8th International Conference on Carbonaceous Particles in the Atmosphere
Vienna, Austria
September 14, 2004
Outline
Introduction
BC ageing schemes
CCCma GCM burdens, concentrations and lifetimes
Comparison with surface layer observations
Conclusions
Direct effect
Indirect cloud lifetime effect
Anthropogenic emissions
SO2
SO4--
BC
OC
Indirect cloud albedo effect
Cloud evaporationSemi-direct effect
Climate Effects of Carbon Aerosol
CCCma AGCM15b overview
3 year model simulations using T47 horizontal resolution (3.75x3.75).
35 vertical hybrid p-σ levels ( lid=50Pa).
Prognostic variables include T, qv, ln(SP), vorticity, divergence, LWC and IWC.
BC treatment in CCCma GCM
80% 20%
λ=24h
Primary Emissions
Hydrophobic BC Hydrophylic BC
Deposition
Transport
Deposition
Transport
BC Burden – fixed 24h halflife
24h Halflife vs. No Ageing
Global and annual mean: 0.23 Tg C vs. 3.26 Tg C
Physical Processes related to ageing
Aerosols
H2SO4
HNO3
O3 OH
Coagulation Condensation
Oxidation
BC ageing schemes
- 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 (8h and 2h) - Night: use aerosol number concentration
Fixed 24h half life
Condensation/coagulation
Oxidation
Oxidative parameterization
Assume ageing occurs by oxidation of a layer of organic material (benzo(a)pyrene) that coats the soot.
Use pseudo-first order decay rate coefficient
Consider - number of surface sites on BC
- surface residence times
- sticking coefficients of O3 and H2O
- O3 and H2O concentrations.
Condensation/coagulationbased parameterization
Day-time: above 250m τ = 2h below 250m τ = 8h Modification: if N<300 then τ = 35h
Night-time: if N<4100/cm3 then τ = exp(-aN + b) if N>4100/cm3 then τ = (c + d/N) where a = 2.3012e4 ; b = 4.4428 c = 3.8585 ; d = 1.48e5
Internal mixture of:
- sulfate
- BC (hydrophylic)
- OC (hydrophylic)
- dust (acc mode)
- sea salt (acc mode)
Internally mixed concentration
BC global and annual means
No-ageing
Fix-life
Cond-coag
Mod- cond-coag
Oxid Mod-cond-coag-oxid
Emissions (Tg C/yr)
13.09 13.09 13.09 13.09 13.09 13.09
Burden (Tg C)
3.26 0.23 0.17 0.19 0.32 0.18
Lifetime (d)
90.8 6.5 4.7 5.4 8.9 5.1
Wet Deposition (Tg C/yr)
7.74 9.19 9.14 9.12 9.10 9.09
Dry Deposition (Tg C/yr)
4.95 3.90 3.95 3.97 3.99 4.00
Alert, Canada
Data from Sharma et al. (2004)
Amsterdam Island
(Wolff and Cachier 1998)
Mace Head, Ireland
(Cooke et al. 1997)
Uji, Japan
Data from Höller et al. (2002)
IMPROVE USA domain mean
Vienna & Streithfen data
Data courtesy of H. Puxbaum & A. Salam
Model/observations ratios
Ratios of annual mean
surface layer concentration (model/obs)
Austria USA Japan Alert No-ageing
1.96 4.18 0.38 23.85
Fix-life 1.27 0.77 0.18 3.84 Cond-coag
1.11 0.66 0.16 2.99
Mod-cond-coag
1.16 0.73 0.17 3.22
Oxid 1.30 0.84 0.19 4.33 Mod-cond-coag-oxid
1.13 0.63 0.16 3.02
Model/observations ratios
Ratios of annual mean surface layer concentration (model/obs)
Amsterdam Island
Mauna Loa
Mace Head
Antarctica
No-ageing
66.16 157.7 5.83 308.37
Fix-life 3.84 4.04 1.03 19.97 Cond-coag
2.99 2.73 0.86 17.60
Mod-cond-coag
3.22 3.36 0.90 21.64
Oxid 4.33 5.76 1.18 23.68 Mod-cond-coag-oxid
3.02 3.16 0.86 20.15
Conclusions
Preliminary results show that ageing based on a condensation/coagulation scheme (Riemer et al. 2004) gave the lowest annual and global mean burdens.An oxidative scheme gave the highest burdens.A physically based BC aging treatment is desirable in a GCM and allows the BC life to respond to regional conditions.Reasonable BC burdens can be predicted with the coagulation/condensation/oxidation parameterization.The global BC burden and ultimately the climate forcing is highly sensitive to the BC ageing parameterization in a global climate model.
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