1. Progress on the unification of the SO 2 retrieval for GOME-2A/B and OMI C. Hörmann, S. Beirle, K. Mies and T. Wagner First German S5P Verification Meeting Bremen November 28 and 29, 2013

2. Unification of SO 2 DOAS retrieval - Same DOAS fit properties for all 3 instruments (GOME-2A, GOME-2B, OMI): - Fit range: 312.1-324 nm - Used absorption cross sections: SO 2 223K (Bogumil et al.) O 3 223K (Bogumil et al.) O 3 223K * λ additional O 3 cross sections to correct O 3 223K ^ 2 for AMF wavelength dependence (Pukite et al., 2011) Ring Inverse reference ( straylight correction) - Calibration via single reference spectrum for GOME-2A/B, individual reference spectra for each OMI detector raw

3. New SO 2 DOAS retrieval for OMI Daily de-striping by subtraction of detector raw dependent offset from Pacific reference sector (red orbit stripes on April 1 due to „OMI Zoom Mode“  individual calibration needed?!?)

4. Daily data: OMI SO 2 VCD (geo.) lat. dependent offset still visible eruption of Piton de la Fournaise  Substraction of latitudinal dependent offset (calculated for each grid row, i.e. 0.1°)

5. offset corrected Daily data: OMI SO 2 VCD (geo.)

6. Comparison to GOME-2A SO 2 VCD (geo.)  Good agreement, only small differences because of different overpass time

7. GOME-2A OMI Mean latitudinal SO 2 VCD (without latitudinal offset correction) Latitude [°N] Mean SO 2 VCD

8. GOME-2A OMI Mean latitudinal SO 2 VCD (latitudinal offset corrected) Latitude [°N] Mean SO 2 VCD

9. Monthly mean: OMI SO 2 VCD (geo.) offset corrected lat. dependent offset again visible interference with topography and bright surfaces ice edge visible

10. Comparison to GOME-2A SO 2 VCD (geo.)  Very good agreement  Less interference with topography because of pixel size? less interference with topography

11. GOME-2A OMI Latitude [°N] Mean SO 2 VCD Mean latitudinal SO 2 VCD (without latitudinal offset correction)

12. GOME-2A OMI Latitude [°N] Mean SO 2 VCD Mean latitudinal SO 2 VCD (latitudinal offset corrected)

13. GOME-2A vs. OMI (monthly mean)  Good agreement between GOME-2A and OMI for monthly mean  Best correlation for Norilsk region probably because of fairly constant emissions Popocatépetl/Mexico City Nyiamuragira Norilsk (volcanic/anthropogenic) (volcanic) (anthropogenic) 1:1 slope

14. Comparison of GOME-2A vs. GOME-2B data format problem (contact R. Lang)  GOME-2A data quality decreased due to degradation (σ 2013 ≈ 2 ∙ σ 2007 )  due to narrow swath, global coverage after ≈ 4.5 days

15.  good agreement (almost same overpass time)  GOME-2B data blurred compared to GOME-2A (larger pixel size) GOME-2B SO 2 VCD

16. GOME-2A GOME-2B Latitude [°N] Mean SO 2 VCD Mean latitudinal SO 2 VCD (without latitudinal offset correction) strong latitudinal offset (unknown origin)

17. GOME-2A GOME-2B Latitude [°N] Mean SO 2 VCD Mean latitudinal SO 2 VCD (latitudinal offset corrected) Very good agreement after latitudinal offset correction

18. GOME-2A vs. GOME-2B (monthly mean)  Good agreement between GOME-2A and GOME-2B for monthly mean  Large scatter visible in GOME-2A data Popocatépetl/Mexico City Nyiamuragira Nevado del Ruiz (volcanic/anthropogenic) (volcanic) (volcanic) 1:1 slope

19. Plans for the near future 1)Further improving SO 2 fit (  especially GOME-2A/B) 2)Comparison of timeseries/annual maps (e.g. China, Norilsk…) 3)Evaluation of SCIAMACHY data 4)Implementation of SO 2 DOAS fit at larger wavelengths for OMI + combination approach + intercomparison GOME-2A/B/OMI 5) Analysis and comparison of test data (CAMELOT)