1. SADDU Meeting, 10-11 March 2009, SRON, Utrecht1 Recent progress on nadir UV-Vis retrievals at BIRA M. Van Roozendael 1 C. Lerot 1, I. De Smedt 1, N. Theys 1, J. van Gent 1, R.S. Spurr 2 1 Belgian Institute for Space Aeronomy (IASB-BIRA) 2 RT-Solutions, Inc.

2. SADDU Meeting, 10-11 March 2009, SRON, Utrecht2 Content  Highlights of BIRA activities within SQWG (C. Lerot)  Progress on total ozone retrieval (GDP-5 project)  Status of CH 2 O retrievals (I. De Smedt)  Recent progress on tropospheric BrO retrievals (N. Theys)

3. SADDU Meeting, 10-11 March 2009, SRON, Utrecht3 BIRA contribution to the SQWG (1) Total ozone  The BIRA algorithm SDOAS has been implemented in the SCIAMACHY operational processor OL v3.  Comparisons with independent measurements from other instruments show consistent results (GOME, OMI, ground-based stations).  Slight decreasing trend (approx. -2% over full period) probably related to calibration issues. Currently investigated by level 1 experts of the SQWG. SCIAMACHY - OMI (%) SCIAMACHY - reference (%) GOME OMI TOSOMI/SCIAMACHY Ground-based C. Lerot et al., Atmos. Meas. Tech. Discuss., 1, 249-279, 2008

4. SADDU Meeting, 10-11 March 2009, SRON, Utrecht4 BIRA contribution to the SQWG (1) Very preliminary: A slight positive trend is observed in the differences between columns retrieved using L1 v8 and L1 v6 data (very limited sample of orbits).  Using the L1 v8 files could improve the temporal stability of the retrieved SCIAMACHY total O 3 columns. To be confirmed with more data !! Impact of new level-1 version 8 (O 3 (L1 v8) - O3(L1 v6.03) Total ozone + 2 % (2002-2008)

5. SADDU Meeting, 10-11 March 2009, SRON, Utrecht5 BIRA contribution to the SQWG (2) Total NO 2  Recommendation of retrieval settings to derive high-quality total columns. SCIAMACHY total NO 2 columns (molec/cm²)  Temporal stability of measurements, allowing for detection of geophysical change in the NO 2 abundances (e.g. impact of the Quasi-Biennial Oscillation on the NO 2 background in equatorial regions). QBO impact GOME-2 SCIAMACHY  Consistency of the SCIAMACHY NO 2 columns with the measurements from other instruments

6. SADDU Meeting, 10-11 March 2009, SRON, Utrecht6 BIRA contribution to the SQWG (3) Total BrO  Test of different retrieval settings to establish baseline for BrO SCD retrieval.  Recommended interval: 336- 351 nm  BrO cross-sections Fleischmann et al.  Consistency of the SCIAMACHY BrO columns with measurements from other instruments ? Average SCDs in a 20° latitude zone around equator 7.69 molec/cm 2 9.78

7. SADDU Meeting, 10-11 March 2009, SRON, Utrecht7 BIRA contribution to the SQWG (3) Total BrO  GDOAS SCIAMACHY BrO  Preliminary comparison for 2 GB stations  Good agreement in Harestua, less good in Lauder. More work ongoing.

8. SADDU Meeting, 10-11 March 2009, SRON, Utrecht8 GDP-5 project (PI. D. Loyola, DLR)  Implementation of GODFIT code in the GOME operational processor v5.  Total ozone derived by direct-fitting to GOME radiances in 325-335 nm using on-line LIDORT calculations of spectral radiances and O 3 column Jacobians.  The derived columns are more accurate than obtained with simple DOAS approach (GDP-4), especially at high solar zenith angles. Residual cyclic signatures in the satellite/ ground-based differences are reduced. GOME – Ground-based (%)

9. SADDU Meeting, 10-11 March 2009, SRON, Utrecht9 GDP-5 project (T-shift scheme) Demonstration of new T-shift retrieval procedure in GODFIT O 3 layer - One supplementary parameter is introduced in the fit: T shift. - The original a-priori input temperature profile is shifted by the value derived in the fit. Effective temperatures  T-shift leads to effective temperatures close to the ones derived from ECMWF profiles.  T-shift is stable, converges in all cases, and is weakly dependent on a-priori input (ECMWF T-field are not needed any more).  T-shift is more accurate in case ECMWF fails (e.g. O 3 hole conditions)

10. SADDU Meeting, 10-11 March 2009, SRON, Utrecht10 Status of CH 2 O retrievals 2003-2008 I. De Smedt, BIRA

11. SADDU Meeting, 10-11 March 2009, SRON, Utrecht11 Consolidation of SCIAMACHY settings  Reprocessing of the offline LV1 dataset (version 6.03).  Calibration options: 0,1,2,3,4,5,6 (no radiometric calibration).  For consistency purposes, GOME and SCIAMACHY have been reprocessed with the same datasets of high resolution absorption cross-sections.  CH 2 O: Meller, 1992. 298K.  NO 2 : Vandaele, 2002. 220K, i0 correction.  O 3 : Brion, 1998. 228K and 243 K, i0 correction.  BrO: Fleischmann, 2004. 223K.  OClO: Bogumil, 2003. 293K.  Ring: Gaussian slit function, SCIAMACHY irradiance of 20030329, KPNO solar spectrum.  Polarisation: SCIAMACHY u2 and u3 vectors in channel 2.  Analysis windows: 328.5-346 nm.  Reference spectrum: average of 20 radiance spectra selected daily in the Pacific Ocean ([-10 10]-[180 220]).

12. SADDU Meeting, 10-11 March 2009, SRON, Utrecht12 Review of CH 2 O cross-sections in the CH 2 O retrieval region (320-360 nm). at SCIAMACHY resolution. Compared to Meller, 2000 which is the current reference Cantrell (1990) is 10% lower. Bogumil (2003) agrees within 1%. Gratien (2007) is 11% higher !

13. SADDU Meeting, 10-11 March 2009, SRON, Utrecht13 How does SCIAMACHY perform compared to GOME? Tropospheric columns: Regional Mean. Monthly averages. Pixels with CF<=40%. Comparison with IMAGES. GOME and SCIAMACHY VCDs agree.

14. SADDU Meeting, 10-11 March 2009, SRON, Utrecht14 How does SCIAMACHY perform compared to GOME? Fitting residuals/ number of observations: Shorter integration time for SCIAMACHY pixels  less favorable S/N ratio than for GOME  higher fitting residuals. Trend follows degradation. SCIAMACHY pixels 7x smaller than GOME pixels but nadir-limb views alternate  ~ 3,5x more SCIAMACHY pixels.

15. SADDU Meeting, 10-11 March 2009, SRON, Utrecht15 Retrieval of tropospheric BrO  Aim: develop generic tropospheric BrO retrieval algorithm, applicable to e.g. GOME, SCIAMACHY, GOME-2, etc.  Method: residual tropospheric BrO retrieved in three steps: - Retrieval of BrO SCDs using the DOAS method  harmonization of BrO DOAS settings - Stratospheric BrO columns determined from new dynamical climatology of stratospheric BrO using, as input parameters, O 3 and NO 2 columns measured by same sensor. (Theys et al., ACP, 2009) - Air mass factors are applied to account for changes in measurement vertical sensitivity due to clouds and surface reflectivity.

16. SADDU Meeting, 10-11 March 2009, SRON, Utrecht16 Dynamical BrO climatology Stratospheric BrO concentrations are driven by: the dynamic of the atmosphere and the photochemistry Concept: develop two distinguished climatologies  Br y (dynamical aspect)  BrO/Br y (photochemistry) Theys et al., A global stratospheric bromine monoxide climatology based on the BASCOE chemical transport model, Atmos. Chem. Phys., 2009 (accepted)  Based on BASCOE 3D-CTM

17. SADDU Meeting, 10-11 March 2009, SRON, Utrecht17 Photochemistry: BrO/Br y climatology In the lower stratosphere, BrO/Br y depends to the 1 st order on the NO 2 concentration : - : reaction rate coeff. BrO+NO 2 +M→BrONO 2 +M - : loss rate of BrONO 2 (mainly photolysis) → BrO/Br y profile climatology can be constructed using a parameterization based on: ■ stratospheric NO 2 VCD ■ solar zenith angle (diurnal variation)

18. SADDU Meeting, 10-11 March 2009, SRON, Utrecht18 Results Stratospheric BrO columns +error (%) from the climatology for typical O 3 and NO 2 columns at GOME overpass (monthly zonal mean) SZA<80°  monthly-zonal version generated for SQWG

19. SADDU Meeting, 10-11 March 2009, SRON, Utrecht19 Validation Ground-based (60°N) 12-20 km BrO partial columns SCIAMACHY limb 15-30 km BrO partial columns (zonal mean) LPMA/DOAS balloon

20. SADDU Meeting, 10-11 March 2009, SRON, Utrecht20 Application  e.g. GOME-2 BrO Total StratoTropo

21. SADDU Meeting, 10-11 March 2009, SRON, Utrecht21 Thank you for your attention