Page 1 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 Validation of OMI trace gas products Main contributors (this work): Michel Van Roozendael 1, I. De Smedt 1, N. Theys 1, G. Pinardi 1, F. Goutail 2, T. Wagner 3 1 BIRA-IASB 2 CNRS-SA 3 IUP Heidelberg AO 2931 (cont.)

Page 2 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 Content F Objectives F First results on validation of OMI: u BrO columns u HCHO columns u Tropospheric NO 2 columns F Summary and outlook

Page 3 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 OMI trace gas validation within AO 2931 F Aim: assess the geophysical consistency of the OMI trace gas products based on: u Inspection of general behaviour: are there obvious artefacts? u OMI versus other satellites: are there systematic deviations? u OMI versus correlative ground-based data: are the products in line with reference ground-based data sets? u Scientific retrievals: help interpreting validation results and support OMI algorithm teams with F Target OMI trace gas products: (O 3, NO 2 ), BrO, HCHO, tropospheric NO 2, (OClO, SO 2 )

Page 4 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 Means  correlative data sets (1) F Satellites products (BrO, HCHO, tropospheric NO 2 ) u N UV-vis scientific products developed at IFE Bremen, IUP Heidelberg, KNMI and BIRA-IASB u GOME (global until June 2003, afterwards NH) u SCIAMACHY (global from Jan 2003 onwards) F Ground-based DOAS/MaxDOAS monitoring stations u SAOZ network u BIRA stations (Harestua 60°; OHP 44°N; Reunion 22°S) u BREMDOM network (~ 6 sites) u Heidelberg stations (~ 4 sites) F Campaigns  DANDELIONS, SAUNA, etc

Page 5 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 Polarstern Cruise ANTXXI/1 Differences between measured Slant Column densities for elevation angles 3 or 10 and that of zenith indicate tropospheric BrO concentration during ANTXI/1 Enhanced tropospheric BrO in regions where also organic Br compounds are enhanced O. Ibrahim, T. Wagner, IUP Heidelberg University of Heidelberg

Page 6 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006

Page 7 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 BrO columns validation F Polar plumes not covered by AVDC overpass stations F Only 6 months of OMI data (Nov 2005  May 2006) F “Single pixel” overpass noisy  monthly averaging required F Lots of “outliers” that must be filtered out from the product Overpass data available from AVDC

Page 8 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 BrO columns: OMI vs GOME and SCIAMACHY

Page 9 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 BrO columns: OMI vs ground-based DOAS

Page 10 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 BrO columns: summary F Good correlation with GOME and SCIAMACHY BrO F …but OMI columns are systematically lower by approx. 50% F Origin of the discrepancy?? u Instrumental issue? u OMBrO fitting interval? u Lv1 data awaited by validation teams…

Page 11 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 HCHO columns validation Overpass data available from AVDC GOME HCHO

Page 12 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 HCHO columns: OMI vs GOME and IMAGES

Page 13 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 HCHO columns: summary F Strong seasonal pattern in OMI HCHO F Largest in summer and Northern Hemisphere. F Basically cancels at 4O°S F Possible origin?? u Instrumental effect? u Daily reference spectra taken around 40°S? u Lv1 data awaited by validation teams…

Page 14 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 Tropospheric NO 2 F Challenging aspects of tropospheric NO 2 validation: u Large small-scale gradients in both time and space (4-D)  Co-location and representativity issues: H Spatial extent of satellite footprint H Time coincidence H Adequacy of vertical sampling H Cloud sensitivity etc F Approach for this AO: make use of available ground- based DOAS and MaxDOAS observations 1)NO 2 pollution monitoring using SAOZ in Paris 2)MaxDOAS during DANDELIONS

Page 15 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 NO 2 pollution monitoring above Paris using SAOZ measurements (1) Uv-visible zenith sky spectrometer, nm, O 3, NO 2, located inside Paris (on the roof of Univ.) F. Goutail, F. Borchi, A. Bazureau, D. Ionov, J. Abadie, M. Valamanesh Service d’Aéronomie CNRS/IPSL, F. Meleux, INERIS Tropospheric NO 2 Tropospheric NO 2 calculated from total column NO 2 minus stratospheric NO 2 (strat. NO 2 from OHP clean air station in southern France). Validated using Airparif in- situ data.

Page 16 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 NO 2 pollution monitoring above Paris using SAOZ measurements (2) One year of comparison: There are periods with very good agreement and periods with underestimation by OMI. Zoom on period after October 23, 2005: 2 sets of OMI data: - AVDC (Tropospheric NO2) - TEMIS (from the plots on website)

Page 17 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 MAXDOAS during DANDELIONS F Cabauw NL, May-June 2005 F 3 MaxDOAS (IFE, IUP, BIRA) u Tropospheric NO 2 columns retrieved using geometrical assumption u No dependency on NO 2 profile shape u Retrieval possible under cloudy conditions (high clouds, above NO 2 layer) A. Richter, IFE

Page 18 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 IFE Bremen vs BIRA MaxDOAS NO 2 Correlation coeff: 0.81

Page 19 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 MaxDOAS vs OMI and SCIAMACHY NO 2  Good matching with GB MaxDOAS for both OMI NO 2 products

Page 20 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 Comparison of cloud top pressure data products  SCIAMACHY FRESCO “sees” higher clouds than OMI cloud products

Page 21 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 Impact of spatial averaging effect? F SCIAMACHY NO 2 possibly biased due to its larger footprint size.  OMI might help quantifying this effect SCIAMACHY footprint

Page 22 OMI ST Meeting #11, KNMI, De Bilt, The Netherlands, June 2006 Summary F BrO columns: OMI underestimates GOME, SCIAMACHY and ground-based data by approx. 50% F HCHO columns: large seasonal artefact, mostly prominent in Northern hemisphere F Tropospheric NO 2 : u Urban region (Paris)  tendency to underestimate local columns u Cabauw DANDELIONS  good agreement with MaxDOAS