1. Validation of OMI and SCIAMACHY tropospheric NO 2 columns using DANDELIONS ground-based data J. Hains 1, H. Volten 2, F. Boersma 1, F. Wittrock 3, A. Richter 3, T.Wagner 4, M. Van Roozendael 5, R. Dirksen 1, M. Kroon 1, and P. Levelt 1 1. KNMI, De Bilt, The Netherlands, contact:hains@knmi 2. RIVM, Bilthoven, The Netherlands 3. University of Bremen, Bremen, Germany 4. Max-Planck Institute for Chemistry 5. BIRA-IASB, Brussels, Belgium OMI Science Team Meeting June 25, 2008

2. Outline Describe tropospheric NO 2 observations. Comparisons among ground based instruments. Compare ground based instruments with satellite. Investigate influence of measurements on OMI tropospheric NO 2 retrieval. Introduce possible NO 2 instrument comparison – Summer 2009

3. Dutch Aerosol and Nitrogen Dioxide Experiments for vaLIdation of OMI and SCIAMACHY DANDELIONS 2006 Time  8-13 and 20-22 September 2006. Conditions  Clear skies and fair weather, Cabauw The Netherlands. Ground based instruments  3 MAXDOAS (BIRA, University of Bremen and University of Heidelberg), RIVM lidar profiles and in-situ concentrations from chemiluminescence instruments at surface and on top of 200 m tower. –RIVM aerosol lidar observed the planetary boundary layer height (PBL). –Ground based instruments sample different directions. Satellites  OMI and SCIAMACHY DOMINO products.

4. Cabauw industry Clean air CESAR The Site industry

5. PBL In- situ MAX DOAS Lidar Scattering Conc. (7 altitudes) + PBL height (aerosol lidar)  VC pbl OMI and SCIAMACHY DOMINO Tropospheric NO 2 vertical column (VC t ) SCIAMACHY pixel size 30x60 km 2. OMI pixel size 13x24 km 2 (nadir). VC t = VC pbl + VC ft Concentration (0, 200 m) + PBL height (aerosol lidar)  VC pbl Slant column + geo AMF  VC t

6. Comparisons among ground based instruments 1:1

7. Comparisons among ground based instruments 1:1 In-situ observes more NO 2 than lidar  NOy bias (PAN, HNO3 etc.)

8. 1:1 Comparisons among ground based instruments 1:1 Comparisons are good (instruments sample different directions). MAXDOAS observes more NO 2 than lidar  in lidar integration free tropospheric NO 2 = 0.

9. Comparisons with satellite Comparisons are good considering differences in spatial and temporal resolution. + pixel size <650 km 2 + pixel size > 650 km 2 + SCIAMACHY 1:1

10. Comparisons with satellite + pixel size <650 km 2 + pixel size > 650 km 2 + SCIAMACHY

11. 1:1 3 MAXDOAS, lidar and in-situ + pixel size <650 km 2 + pixel size > 650 km 2 + SCIAMACHY OMI and SCIAMACHY DOMINO products are within 33% of ground based observations.

12. Plausible explanations for the difference MAXDOAS and satellite use different AMF. In-situ has positive bias due to NO y interference. OMI and SCIAMACHY are affected by clouds. Satellite observations represent a large ground pixel (e.g. OMI nadir pixel is 13 x 24 km 2 ) while ground- based observations are point measurements. Ground based instruments have not been thoroughly compared with each other or compared with in-situ aircraft profiles - plan for future campaign.

13. Level 1B Slant column NO 2 Stratospheric Slant column NO 2 Tropospheric Slant column NO 2 Stratospheric Vertical column NO 2 Tropospheric Vertical column NO 2 TM4- DOMINO AMF Strat AMF Trop TM4- global chemistry transport model run with assimilated OMI products TM4 produces NO 2 profiles These NO 2 profiles are used to calculate AMFs (air mass factors). OMI tropospheric NO 2 algorithm TM4- DOMINO

14. Can we improve the algorithm ? Examine a-priori profile shape in TM4 model. Compare TM4 profile with lidar profile How does NO 2 change with revised AMF.

15. Steps to Compare lidar with TM4 NO 2 1.Interpolate/Extrapolate Lidar. 2.Regrid observation to 1hpa grid. 3.Integrate NO 2 between TM4 levels  partial columns.

16. OMI (original and revised AMF) and average ground based NO 2 observations.  Small changes.  TM4 profiles are good assumptions. Statistics for comparisons Percent difference standard deviation Correlation coefficient Original36%29%0.76 Revised35%30%0.77

17. OMI pixel width < 50 km

18. Compare TM4 and lidar profiles TM4 NO 2 peaks at lower level than lidar. OMI less sensitive to original TM4 profile.  AMF is too small.  OMI NO 2 is too large.

19. Conclusions Ground based NO 2 instruments compare well with each other (r ~.6). OMI and SCIAMACHY (DOMINO) compare well with average ground based NO 2 (within 33%). Comparisons among instruments are good considering the differences in retrieval techniques and temporal and spatial resolution. These results are fair weather biased. Including lidar tropospheric NO 2 profiles in the AMF calculation did not affect the AMF  TM4 profiles are good assumptions.

20. Tentative plans for CEOS/GEOMON NO 2 instrument comparison Possible Goals: Surface campaign (like DANDELIONS) ~15 instruments (MAXDOAS, lidar and in-situ monitors). –NDACC blind test. Observations support OMI and SCIAMACHY validation. 1 st part - compare instruments. 2 nd part - move the instruments to sites wihtin a pixel. Improve understanding of NO 2 variability in the area of a satellite pixel. Location: Europe, possibly Cabauw, The Netherlands When: Summer 2009 Participants: Europe, N. America, Asia

21. + pixel size <650 km 2 + pixel size > 650 km 2 + SCIAMACHY Operational DOMINO

22. Comparisons with DOMINO Comparisons with Standard product

23. Compare TM4 with lidar profile

25. Lidar profile measurements MAXDOAS Tropospheric NO 2 VCD retrieved using geometric AMF NO 2 layer LOS SCD off SCD zen