Black Carbon Ageing in the CCCma AGCM

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-s levels to 50 hPa.
• Prognostic variables include T, qv, ln(ps),
  vorticity, divergence, liquid and ice water
  content.

5
BC treatment in CCCma GCM

• 80
  20
  
  
• 
  
• ?24h

Primary Emissions
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

• Aerosols
  
• 
  
• 
  H2SO4
• 
  HNO3
• 
  
• OH
  
• O3
  

Coagulation
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
(No Transcript)
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
red obs black-o- FIX-LIFE green
COND-COAG-OXID black OXID
blue -o- NO-AGEING
20
Model to observation comparison
21
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.