1. Comparison of OMI NO 2 with Ground-based Direct Sun Measurements at NASA GSFC and JPL Table Mountain during Summer 2007 George H. Mount & Elena Spinei Washington State University Stanley P. Sander, Thomas Pongetti**, and Shuhui Wang** NASA JPL Jay Herman and Alexander Cede NASA GSFC ** = next talks

2. Participating Instruments WSU MultiFunction DOAS (MFDOAS) - basic measurement: slant column observes direct sun or scattered skylight (DS + MAXDOAS) spectral coverage: 281 - 498 nm CCD - 13.5 µm pixel size spectral resolution 0.83 nm spectral sampling on FWHM 7.8 pixels DS uses an integrating sphere integration time: sub-second GSFC PANDORA - basic measurement: slant column observes direct sun spectral coverage: 265 - 500 nm CCD - 25 µm pixels spectral resolution 0.4 nm spectral sampling on FWHM 2 pixels integration time: sub-second time averaged to 20-sec JPL UVFTS - basic measurement absolute slant column observes direct sun spectral regions used for analysis: 488 - 498 nm spectral resolution: 0.001 nm integration time: 17 min - observes opposite limbs of sun

3. data analysis MFDOAS and PANDORA reduce raw data to slant column using a common reference spectrum from a particular date/time nonlinear least squares using common cross section (Harder et al., 1997) --> difference between absolute slant column at time of measurement and the absolute slant column in the reference spectrum determine absolute slant column in the reference spectrum using Langley method, bootstrap method, UVFTS - all are consistent at TMF where clean skies were observed part of the time correction: 0.13 + 0.01 DU at TMF, 0.25 + 0.01 DU at GSFC for the reference spectra used at each location apply AMF from direct sun (simple geometry), remove data with SZA > 80° to avoid problems with layer height in AMF calculation UVFTS Tom Pongetti and Shuhui Wang will talk about the FTS data analysis technique in the next talks

4. Campaigns Goddard Space Flight Center data every day 14 - 25 May 2007 PANDORA - direct sun on ~ 20 sec centers MFDOAS –direct sun on ~ 1 sec centers –direct sun + scattered sky at 4 azimuths and 4 elev angles ~ 20 min about half the days were devoted to scattered sky + DS measurements JPL Table Mountain data every day from 2 July - 12 July 2007 PANDORA and MFDOAS as above UVFTS - 17 min cycles on each of the two solar limbs Only direct sun observations are presented here OMI data is collection 3

5. comparison of MFDOAS and PANDORA at the two locations

6. DS-DOAS vs UVFTS measurements at TMF ground = 0.93 * UVFTS

7. NO 2 Vertical Column Density at GSFC 14 May 2007

8. NO 2 Vertical Column Density at GSFC 15 May 2007

9. NO 2 Vertical Column Density at GSFC 23 May 2007

10. NO 2 Vertical Column Density at GSFC 24 May 2007

11. fitted slope: ~ 1.2 OMI = 1.2 x ground OMI vs. Ground Based Total NO 2 Vertical Column at GSFC

12. Temporal Variability of Total NO 2 Vertical Columns (GSFC: 14-May-07)

13. wave structure of NO2 coming across GSFC of ~ 1 min period

14. NO 2 Vertical Column Density at JPL TMF 3 July 2007

15. NO 2 Vertical Column Density at JPL TMF 6 July 2007

16. NO 2 Vertical Column Density at JPL TMF 7 July 2007

17. NO 2 Vertical Column Density at JPL TMF 12 July 2007

18. 3b __ 9 7 8 11z 2z 6 4 10b 12b 10a 3a 12a TMF region - numbers are dates in July of the OMI observations and are placed at the pixel center; “z” = OMI zoom mode, “a” and “b” indicate overpasses on the same day 10 km JPL

19. OMI vs. Ground Based Total NO 2 Vertical Column at JPL-TMF (July 2007)

20. Conclusions successful campaigns were carried out in summer 2007 at GSFC and JPL TMF with 3 instrument groups measuring NO 2 excellent agreement between instruments was found, even on time scales of minutes UVFTS was extremely valuable --> absolute column & confirmation of calibration for the reference column of NO 2 for PANDORA and MFDOAS need a large number of days to get a solid comparison with OMI comparisons with OMI total NO 2 were difficult due to: –spatial inhomogeneities especially true at TMF - the high elevation and proximity to LA (Tom’s talk next) times when agreement with OMI should have been good and was not wave structure at GSFC showed changes on order 10% in minutes above the site –vertical inhomogeneities movement of polluted air “under” the observing site and inside an OMI pixel OMI NO 2 vertical columns are ~ 15% low at GSFC & poor correlation at TMF use of scattered sky data is valuable (e.g. MFDOAS at PNNL in Washington), but requires a much more difficult interpretation due to calculation of AMF, vertical structure of NO 2, aerosol loading, and spatial inhomogeneities - we are working with PK on use of a combination of near simultaneous DS and scattered sky measurements to improve the analysis

21. Future MFDOAS –detailed reduction of campaign scattered sky data –determinations of ozone and formaldehyde –campaigns which will be used for OMI comparison (DS+scatt sky): WSU fall/winter 2007/2008 PNNL Richland, WA - spring 2008 wildfire measurements late summer 2008 Boise, Idaho December 2008 Houston, Texas April-May 2009 US SE for formaldehyde validation Spain(?) international campaign - summer 2009 or 2010 PANDORA –deployment of PAN-3 for sun, sky, moon –improved tracking and s/n –build network of 15 instruments to map OMI sub-pixel variation and regional variation UVFTS - Tom and Shuhui in next talks

22. NO 2 Vertical Column Density at JPL TMF 4 July 2007

23. NO 2 Vertical Column Density at JPL TMF 8 July 2007

24. NO 2 Vertical Column Density at JPL TMF 11 July 2007

25. NO 2 Vertical Column Density at JPL TMF 9 July 2007

26. NO 2 Vertical Column Density at GSFC (21 May 2007)