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Two Layer Retrieval Method

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Two Layer Retrieval Method

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  1. Retrieval of NO2 absolute columns in the stratosphere and troposphere from ground-based UV-visible measurements with the Fourier Transform Ultraviolet Spectrometer (FTUVS) at Table Mountain, California: Updated method and comparison to OMI.Thomas J. Pongetti, Shuhui Wang, and Stanley P. SanderJet Propulsion Laboratory California Institute of Technology

  2. Two Layer Retrieval Method Simultaneous fit of stratospheric and tropospheric reference is constrained by the total column method described by Shuhui. 40 km 30 20 10 High resolution Strat/Trop references High resolution measured spectrum Input Strat/Trop partition Sample Spectral fits Total Column Method: Vertical information Reduction As described by Shuhui Simultaneous Two layer Method: High Resolution retrieval constrained by the total column method output not = input output = input Stop Output Strat/Trop partition

  3. Comparison to OMI From April 2005 to Present Terrain image of Table Mountain’s surrounding area looking South West. Including OMI pixel center points that coincide with FTUVS days. The L.A. Mountain Range typically separates the L.A. pollution from the clean desert air. Los Angeles Tejon Pass SW Los Angeles County Mountains Cajon Pass High Desert

  4. Diurnal Variations at Table MountainUnpolluted Polluted Strat Trop Total Strat Trop Total

  5. Comparison of Stratospheric Vertical Column : FTUVS vs. OMI

  6. Comparison of tropospheric Vertical Column : FTUVS vs. OMIShows dependence upon terrain surrounding TMF Generally the OMI and FTUVS show better agreement when the terrain pressure is closer to the pressure at TMF

  7. Tropospheric Terrain Adjustment The adjustment is applied to the FTUVS Tropospheric column TMF Pressure OMI Terrain Pressure

  8. Comparison of tropospheric Vertical Column : FTUVS vs. OMIFTUVS column adjusted to OMI terrain pressure The terrain adjustment allows for a more accurate tropospheric comparisons.

  9. Comparison of total Vertical Column : FTUVS vs. OMIFTUVS stratospheric + adjusted tropospheric OMI total column is compared to the FTUVS total column with the tropospheric terrain adjustment.

  10. NO2 Seasonal Variation Strato Tropo Total April 2005 2006 2007 2008 Seasons are evident in stratospheric columns, not in tropospheric or Total

  11. Summary • FTUVS provides an absolute two layer retrieval which is directly comparable to the OMI two layer product. • OMI and FTUVS have good agreement in the stratosphere and poor agreement, due to the TMF terrain, in the troposphere. • A terrain adjustment method has been shown to estimate the NO2 which lies below TMF, resulting in better trop. agreement. • Future work includes: rigorous testing of retrieval, profiles, and terrain adjustment; continue acquiring data for long term record; possibly have a more comparison campaigns at TMF.

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