1. Comparison of the aerosol extinction coefficient retrieved from MAX-DOAS measurements to in-situ measurements P. Zieger 1, K. Clemer 2, S. Yilmaz 3, R. Fierz-Schmidhauser 1, U. Friess 3, H. Irie 4, B. Henzing 5, G. de Leeuw 5,6,7, J. Mikkila 7, T. Wagner 8, U. Baltensperger 1, and E.Weingartner 1 1 Paul Scherrer Institut, 2 Belgium Institute for Space Aeronomy, 3 University of Heidelberg, 4 JAMSTEC, 5 TNO, 6 Finnish Meteorological Institute, 7 University of Helsinki, 8 MPI Mainz CINDI workshop at BIRA, 10-12 March 2010, Brussels, Belgium

2. 2 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Rel. humidity Global Atmosphere Watch (GAW) guideline for aerosol light scattering measurements: RH < 30 - 40% To keep continuous light scattering measurements comparable.

3. 3 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Humidified nephelometer (WetNeph) Definition: Scattering enhancement factor WetNeph DryNeph Fierz-Schmidhauser et al., 2010 (AMT)  s scattering coefficient;wavelength Set-up in the Cabauw tower

4. 4 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Measurement example (Cabauw) 02 July 0903 July 0904 July 09 Aerosol scattering coefficient

5. 5 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Measurement example (Cabauw) 02 July 0903 July 0904 July 09 Aerosol scattering coefficient

6. 6 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Measurement example (Cabauw) Scattering enhancement factor

7. 7 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Comparison to MAX-DOAS data Comparison of ambient in-situ measurements with MAX-DOAS measurements (lowest height level 0-200m) Instruments so far: *retrieval height varied 1.Belgian Institute for Space Aeronomy (BIRA) 2.University of Heidelberg (IUPHD) 3.Japan Agency for Marine-Earth Science and Technology (JAMSTEC) 4.Max Planck Institut (MPI)*

8. 8 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Comparison to MAX-DOAS data Ambient aerosol extinction coefficient Absorption coefficientAmbient scattering coefficient  Multi-Angle Absorption Photometer (= 660nm)   =1.05 (Collaud et al., 2010)  No change with hygroscopic growth assumed  DryNeph, WetNeph (=450, 550, 700nm)  RH amb from tower measurements (10-200m)  Interpolation to MAX-DOAS wavelengths (Ångström law)

9. 9 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Comparison to MAX-DOAS data Golden day 24 June 2009

10. 10 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Comparison to MAX-DOAS data Golden day 24 June 2009

11. 11 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Comparison to MAX-DOAS data Golden day 24 June 2009 Ceilometer 24 June 09 (H. Klein Baltink, KNMI)

12. 12 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Comparison to MAX-DOAS data BIRA: entire campaign  BIRA with Cimel retrieval (asymmetry factor and single scattering albedo as input parameter)  Clouds don’t really influence comparison AERONET

13. 13 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Comparison to MAX-DOAS data All instruments MPI retrieval height varied BIRA retrieval repeated with in-situ measured input parameters

14. 14 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Comparison to MAX-DOAS data All instruments – hour of day

15. 15 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Comparison to MAX-DOAS data All instruments – AOD from sun photometer

16. 16 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Comparison to MAX-DOAS data All instruments – PBL height PBL height from ceilometer (H. Klein Baltink, KNMI)

17. 17 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Conclusions -MAX-DOAS and in-situ measurements agree better than expected -Agreement better for low AOD and low PBL cases -Retrieval for BIRA improves with ambient in-situ measurements as input -Possible reasons: - Stability of boundary layer, influence of upper layers, influence of homogeneous gradient of aerosol concentration, influence of clouds (unlikely, checked with AERONET data), … - Losses in the inlet system (unlikely), calibration issues (very unlikely), parameterization of f(RH) (small effect), … - Influence of nitrate partitioning ? -> Bas

18. 18 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Outlook -Further analysis, possibly with additional MAX-DOAS instruments (KNMI and IUPB?), MAX-DOAS: unified assumptions, time grid, etc … -Longer time series will bring further insights and might help to prove or disprove our hypotheses (e.g. IUPHD measured until October) -Add Lidar profiles in comparison -Paper on in-situ comparison will be submitted by the end of June 2010 together with the profile paper

19. 19 Paul Zieger, 2nd CINDI workshop, 10-11 March 2010, Brussels, Belgium Thank you for your attention! … and thank you to all contributors and the CINDI organizers!