SADDU Meeting, 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.

SADDU Meeting, 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)

SADDU Meeting, 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, , 2008

SADDU Meeting, 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 % ( )

SADDU Meeting, 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

SADDU Meeting, 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: 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

SADDU Meeting, 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.

SADDU Meeting, 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 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 (%)

SADDU Meeting, 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)

SADDU Meeting, March 2009, SRON, Utrecht10 Status of CH 2 O retrievals I. De Smedt, BIRA

SADDU Meeting, 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, K.  NO 2 : Vandaele, K, i0 correction.  O 3 : Brion, K and 243 K, i0 correction.  BrO: Fleischmann, K.  OClO: Bogumil, K.  Ring: Gaussian slit function, SCIAMACHY irradiance of , KPNO solar spectrum.  Polarisation: SCIAMACHY u2 and u3 vectors in channel 2.  Analysis windows: nm.  Reference spectrum: average of 20 radiance spectra selected daily in the Pacific Ocean ([-10 10]-[ ]).

SADDU Meeting, March 2009, SRON, Utrecht12 Review of CH 2 O cross-sections in the CH 2 O retrieval region ( 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 !

SADDU Meeting, 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.

SADDU Meeting, 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.

SADDU Meeting, 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.

SADDU Meeting, 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

SADDU Meeting, 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)

SADDU Meeting, 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

SADDU Meeting, March 2009, SRON, Utrecht19 Validation Ground-based (60°N) km BrO partial columns SCIAMACHY limb km BrO partial columns (zonal mean) LPMA/DOAS balloon

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

SADDU Meeting, March 2009, SRON, Utrecht21 Thank you for your attention