Carbonaceous aerosols – a global modeling view 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 Modeling and Analysis University of Victoria,
25
Embed
Carbonaceous aerosols – a global modeling view Betty Croft and Ulrike Lohmann * Department of Physics and Atmospheric Science Dalhousie University, Halifax,
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Carbonaceous aerosols – a global modeling view
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 Modeling and Analysis
University of Victoria, Victoria, B.C. Canada
September Retreat – Propstei St Gerold, Austria – September 21, 2005
Physical and chemical ageing Insoluble BC/POM Soluble/mixed
Aerosols H2SO4 HNO3 OH O3
Coagulation Condensation
Oxidation
BC and POM ageing in GCMs• Insoluble Soluble/mixed• Treatment options 1) Fixed exponential decay 2) Stier et al. (2005) condensation and coagulation explicit 3) Riemer et al. (2003) day: condensation – fixed e-folding time night: coagulation – e-folding time ~ number 4) Oxidation based on Pöschl et al. (2001)
GCM description
• Horizontal resolution: T47 (3.75° x 3.75°).
• Vertical resolution: 35 levels up to 50 hPa.
• Prognostic variables: temperature, specific humidity, surface pressure, vorticity, divergence, and liquid and ice water content.
• 3-year simulations following 5 month spin-up using the CCCma AGCM.
Summary• Global and annual mean burdens (lifetimes) are 0.11 Tg C
(5.0 days) and 0.80 Tg POM (4.4 days) for BC and POM, respectively.
• Physically based ageing is faster than use of a fixed e-folding time (24 h half life) and gives lower burdens.• Chemically based ageing is not well understood and not
modelled.• BC and POM tend to be under-predicted at continental sites
but over-predicted at remote sites. This suggests that emissions are low, but also either the transport is too diffusive or the deposition is too slow.
Future work
• Validation of carbon fields – (AERONET, satellite).
• Validation/improvement of scavenging parameterizations.
• Future climate studies– relatively more open burning emissions while sulphate production is controlled. What is the impact of increasing “carbon domination” on aerosol ageing, removal and concentrations?
Aerosol modeling questions
• What are the main chemical ageing processes for BC and POM?
• How does condensation compete with nucleation?• Relative importance of physical versus chemical
ageing on global scale (BC, POM and dust)?• What are the main secondary organic aerosol
production pathways and global yields?• Can emissions inventory uncertainty be reduced,
and how good are the assumptions about the insoluble fraction of BC and POM emissions?