6. EOS-AURA Science Team Meeting 14-17 September 2009, Leiden Comparison of NO 2 profiles derived from MAX-DOAS measurements and model simulations Folkard Wittrock, Katrijn Clémer and the NO 2 profiling team

7. Objectives of the Bremen workshop in November To present the „state of the art“ in tropospheric profiling of NO 2 (and other trace gases) To identify advantages but also limitations of the different methods To collect ideas how to improve the methods and how to move on in the future e.g. harmonize MAXDOAS instruments and retrievals

8. BIRA MAXDOAS VMR surface layer compared to EMPA in situ MAXDOAS vs. in situ courtesy: Katrijn Clémer, BIRA

9. VMR surface layer compared to Bremen in situ MAXDOAS vs. in situ In situ BREAM GL

10. NO 2 Profile Comparison first comparisons sometimes o.k., sometimes not challenge is to identify what causes the differences -> model study 25 June 23 June

11. IASB-BIRA has provided modeled NO 2 slant columns for UV and visible, using 8 different NO 2 scenarios (profiles) 2 aerosol loadings (AOD 0.14 and 0.54 for 477 nm) aerosol information based on CIMEL data from Cabauw HG phasefunction with asymmetry factor of 0.67 Simulations for June 24, 2009 in Cabauw 10 Elevation Angles (1,2,4,5,6,8,10,15,30,89) SCD error based on real DOAS fit errors plus Gaussian noise Calculations with LIDORT Simulation study

12. Fixed settings for OE retrieval algorithms 0 to 4 km Apriori 1 ppb at the surface, 0.01 ppb at the top S a 100% 2 retrievals per situation and wavelength Height grid 50 and 200m -> In total 64 retrievals In total 5 groups (BIRA, MPI, NIWA, iup Bremen, WSU) have calculated data (4 OE, one „simple“ least squares method, only one result for each situation) Simulation study

14. Bremen retrieval of block profile for low aerosol (UV)

15. Simulation study Bremen retrieval of block profile for high aerosol (UV)

16. Simulation study Exponential low pollution, low aerosol

17. Simulation study Exponential high pollution, low aerosol

18. Simulation study Block low pollution, low aerosol

19. Simulation study Block high pollution, low aerosol

20. Simulation study Very shallow layer, low aerosol

21. Simulation study Less shallow layer, low aerosol

22. Simulation study Uplifted layer, low pollution, low aerosol

23. Simulation study Uplifted layer, high pollution, low aerosol

24. Simulation study Exponential low pollution, high aerosol

25. Simulation study Exponential high pollution, high aerosol

26. Simulation study Block low pollution, high aerosol

27. Simulation study Block high pollution, high aerosol

28. Simulation study Very shallow layer, high aerosol

29. Simulation study Less shallow layer, high aerosol

30. Simulation study Uplifted layer, low pollution, high aerosol

31. Simulation study Uplifted layer, high pollution, high aerosol

32. Simulation study

35. Conclusions OE retrieval methods agree quite well to each other, … but not always to „reality“ VC usually captured well also for difficult conditions Viewing directions towards sun and for high SZA difficult to retrieve Best settings for OE still open: Finer grid gives more details, but tends to more oscillations -> Elena has the solution? UV retrieval seems to be more stable Is OE the best method for MAXDOAS retrievals?

36. Outlook Waiting for more groups to contribute (e.g. JAMSTEC on simulated data, MPI on real data), same deadline as for aerosols -> Mid April Profiling paper: NO 2 profile intercomparison focusing on MAXDOAS capabilities and using LIDAR and in situ as complementary data sets (CWG: F. Wittrock, K. Clemer, H. Irie, S. Beirle?) Draft to be written in April 2010 before EGU

37. Bremen - EMPA Slope : 1.11 Correlation : 0.993 Bremen – RIVM Slope : 0.985 Correlation : 0.992 Comparison of Bremen in situ Instrument with Empa and RIVM (at ground level) Empa sees ca. 10 % more NO2 In situ instruments BLC instruments agree quite well

38. In situ instruments deviation between surface in-situ and 200 m in-situ gives information on boundary layer mixing

39. In situ instruments NO 2 often not well mixed even in the lowest 200 m