Validation of OMI and SCIAMACHY tropospheric NO 2 columns using DANDELIONS ground-based data

1. Validation of OMI and SCIAMACHY tropospheric NO2 columns using DANDELIONS ground-based data J. Hains1, H. Volten2, F. Boersma1, F. Wittrock3, A. Richter3, T.Wagner4, M. Van Roozendael5, R. Dirksen1, M. Kroon1, and P. Levelt1 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 NO2 observations. • Comparisons among ground based instruments. • Compare ground based instruments with satellite. • Investigate influence of measurements on OMI tropospheric NO2 retrieval. • Introduce possible NO2 instrument comparison – Summer 2009

3. DANDELIONS 2006 Dutch Aerosol and Nitrogen Dioxide Experiments for vaLIdation of OMI and SCIAMACHY • 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. CESAR Clean air Cabauw industry industry The Site industry

5. OMI and SCIAMACHY DOMINO Tropospheric NO2 vertical column (VCt) SCIAMACHY pixel size 30x60 km2. OMI pixel size 13x24 km2 (nadir). VCt = VCpbl + VCft Scattering In-situ MAX DOAS Lidar PBL Concentration (0, 200 m) + PBL height (aerosol lidar)  VCpbl Slant column + geo AMF  VCt Conc. (7 altitudes) + PBL height (aerosol lidar)  VCpbl

6. Comparisons among ground based instruments 1:1 1:1

7. Comparisons among ground based instruments 1:1 1:1 In-situ observes more NO2 than lidar  NOy bias (PAN, HNO3 etc.)

8. Comparisons among ground based instruments 1:1 1:1 Comparisons are good (instruments sample different directions). MAXDOAS observes more NO2 than lidar  in lidar integration free tropospheric NO2 = 0.

9. Comparisons with satellite 1:1 + pixel size <650 km2 + pixel size > 650 km2 + SCIAMACHY 1:1 Comparisons are good considering differences in spatial and temporal resolution.

10. Comparisons with satellite 1:1 + pixel size <650 km2 + pixel size > 650 km2 + SCIAMACHY 1:1

11. 1:1 + pixel size <650 km2 + pixel size > 650 km2 + SCIAMACHY 3 MAXDOAS, lidar and in-situ 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 NOy interference. • OMI and SCIAMACHY are affected by clouds. • Satellite observations represent a large ground pixel (e.g. OMI nadir pixel is 13 x 24 km2) 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. OMI tropospheric NO2 algorithm TM4-DOMINO Level 1B Slant column NO2 Tropospheric Slant column NO2 TM4-DOMINO Stratospheric Slant column NO2 TM4-DOMINO AMF Strat AMF Trop Tropospheric Vertical column NO2 Stratospheric Vertical column NO2 • TM4- global chemistry transport model run with assimilated OMI products • TM4 produces NO2 profiles • These NO2 profiles are used to calculate AMFs (air mass factors).

14. Can we improve the algorithm ? • Examine a-priori profile shape in TM4 model. • Compare TM4 profile with lidar profile • How does NO2 change with revised AMF.

15. Steps to Compare lidar with TM4 NO2 • Interpolate/Extrapolate Lidar. • Regrid observation to 1hpa grid. • Integrate NO2 between TM4 levels  partial columns.

16. OMI (original and revised AMF) and average ground based NO2 observations. Small changes.  TM4 profiles are good assumptions. Statistics for comparisons

17. OMI pixel width < 50 km

18. Compare TM4 and lidar profiles TM4 NO2 peaks at lower level than lidar. OMI less sensitive to original TM4 profile.  AMF is too small.  OMI NO2 is too large.

19. Conclusions • Ground based NO2 instruments compare well with each other (r ~ .6). • OMI and SCIAMACHY (DOMINO) compare well with average ground based NO2 (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 NO2 profiles in the AMF calculation did not affect the AMF  TM4 profiles are good assumptions.

20. Tentative plans for CEOS/GEOMON NO2 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. • 1st part - compare instruments. • 2nd part - move the instruments to sites wihtin a pixel. Improve understanding of NO2 variability in the area of a satellite pixel. Location: Europe, possibly Cabauw, The Netherlands When: Summer 2009 Participants: Europe, N. America, Asia

21. Operational + pixel size <650 km2 + pixel size > 650 km2 + SCIAMACHY DOMINO

22. Comparisons with DOMINO Comparisons with Standard product

23. Compare TM4 with lidar profile

24. Compare TM4 with lidar profile

25. SCDzen SCDoff NO2 layer LOS Lidar profile measurements MAXDOAS Tropospheric NO2 VCD retrieved using geometric AMF