1. Assimilation of Aerosol Optical Depth Gé Verver 1, Bas Henzing 1, Peter van Velthoven 1 Cristina Robles-Gonzalez 2, Gerrit de Leeuw 2 1 KNMI, De Bilt, The Netherlands 2 TNO-FEL, The Hague, The Netherlands Retrieval Modeling Assimilation Results Outlook

2. The Assimilation System

3. Retrieval Surface Observations Of aerosol Optical Properties Radiative Transfer Model Lookup Tables Satellite observed radiances at different wavelengths Finding the ‘Optimal’ Combination of Lookup Tables Aerosol Optical Depth (AOD, 

4. Results of AOD retrieval at 659 nm, averaged over February 1999. Retrieval

5. The TM3 model Resolution: 2.5  x 2.5  (fine) or 10  x 7.5  (coarse); 31 layers Chemistry: Background tropospheric chemistry ~100 reactions (gas- and aqueous phase) 26 transported tracers Aerosols: Sulfate and Nitrate Black Carbon (hydrophilic/hydrophobic) Organic Carbon (hydrophilic/hydrophobic) (Dust, Seasalt) Extinction Coefficients: prescribed (for all Carbon species : 9 m 2 /kg, for Sulphate: f(RH)) Transport: ECMWF 6-hourly analysed meteorology Incl. Cloud transport, Turbulent exchange Sources of aerosols: Carbon emission (Cooke, 1999) chemical formation of Sulfate and Nitrate Sinks of aerosols: Dry deposition (Ganzevelt et al., 1998) Wet deposition (Jeuken et al. 2001, Roelofs and Lelieveld, 1995)

6. The Assimilation Procedure Aerosol Optical Depth OI scheme provides: Aerosol mass for each species adjusted following: (Collins et al., 2002) based onand

7. Results for the INDOEX region Without assimilation24 hour forecast ATSR-2 ObservationAnalysis

8. Results for the INDOEX region

9. Conclusion There is a strong impact of the observations on the aerosol distributions The lifetime of the aerosols is long enough to carry the observational information for several days

10. Outlook In the near future major improvements are expected by: 1.Using modeled a priori aerosol profiles in the retrieval 2.Refining and updating source strengths and distributions 3.Better estimations of forecast and observation errors used in the assimilation scheme