1. OMI Validation using the Pandora Spectrometer System Jay Herman, Nader Abuhassan, Alexander Cede 1.Validation of OMI satellite data for Ozone is fairly easy using any one of the well calibrated ground-based instruments (for example, Brewer, Dobson, and Pandora) 2.Validation of trace gases generated at the Earth’s surface or in the boundary layer (for example, NO 2 ) is much more difficult. 3.For NO 2, comparisons can be made with single instruments or area distributed groups of instruments.

2. Basic OMI Validation Problem From satellite we get the average total column NO 2 amount over a certain region compared to a “point” retrieval from the ground. For satellite validation  Use several instruments within one satellite pixel to match the air mass. 2 Goals for Pandora Pandora can do both direct sun (no uncertainty in air mass factor) and sky observations (MAX-DOAS). For specific studies, distribute several Pandora instruments over an OMI pixel For good statistics, get long time series at many locations rather than data from campaigns only. Since many instruments are needed, Pandora keeps the costs for hardware, calibration, operation, and maintenance low!

3. Where is Tropospheric NO 2 Look for the Brown Layer Brown Layer In polluted regions, the low altitude of the NO 2 plume and its limited areal extent are the reasons why OMI NO 2 is difficult to validate

4. Successful NO 2 and O 2 O 2 slant column comparisons at CINDI* (Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments) [Pieters et al., Atm. Meas. Tech. 5, 457-485, 2012; Roscoe et al., Atm. Meas. Tech. 3, 1629-1646, 2010] *Funded by EC/ESA in response to CEOS and NDACC actions 4 O2O2O2O2 NO 2 Has Pandora NO 2 been validated? We have had successful NO 2 column comparisons with MFDOAS and FTUVS at GSFC and JPL-Table Mountain Facility [ Herman et al., J. Geophys. Res., 114 (D13307), 2009; Wang et al., J. Geophys. Res., 115 (D13305), 2010] Slide from Cede et al, ACVE 2013, ESRIN, Frascati, 13 March 2013

5. 80km 220km NASA DISCOVER-AQ campaigns 1 and 2 in Maryland and California 12 Pandoras were deployed at the 1 st DISCOVER-AQ campaign during June - July 2011 in the Baltimore- Washington area 15 Pandoras were deployed at the 2 nd DISCOVER-AQ campaign during January-February 2013 in California’s Central Valley OMI Nadir Pixel OMI Nadir Pixel

6. June-July 2011

7. Jan-Feb 2013

8. NASA DISCOVER-AQ missions 3 and 4 in Texas and Colorado Texas Near Houston Colorado Near Denver June – July 2014 Problem: Separations are too Large for OMI Field of View Need multiple Pandoras in OMI FOV 150 km 30 km OMI Pixel OMI Pixel Sept 2013

11. Pandora intercomparison at GSFC After DISCOVER-AQ campaign Baltimore-Washington Figure shows total NO 2 columns from 11 Pandoras for selected clear sky days in fall 2011

12. Compare Pandora with OMI NASA HQ Washington, DC Ozone NO 2

13. Compare Pandora with OMI NASA HQ Washington, DC O 3 NO 2 Mean values appear fairly good for both O 3 and NO 2 However, correlation for NO 2 is poor

14. Compare Pandora with OMI NOAA Building Boulder, Colorado

15. Compare Pandora with OMI NOAA Building Boulder, Colorado

16. Compare Pandora NO 2 with OMI Moody Tower Houston, Texas

17. DISCOVER-AQ Maryland: Three Sites Within an OMI Pixel

18. Compare Pandora with OMI DISCOVER-AQ Campaigns

19. Summary