Randall V. Martin, Daniel J. Jacob, Paul I. Palmer Kelly Chance, Thomas P. Kurosu James Gleason

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An Improved Retrieval of Tropospheric Nitrogen
Dioxide from GOME

• Randall V. Martin, Daniel J. Jacob, Paul I.
  Palmer Kelly Chance, Thomas P. Kurosu
  James Gleason
• Harvard University
  Harvard-Smithsonian Center for Astrophysics
  NASA Goddard Space Flight Center
• Tropospheric Air Mass Factor Calculation
• General formulation
• Scattering by clouds
• Application to GOME
• Slant Column Fitting
• Determination of the Non-tropospheric column
• Tropospheric Columns
• Slant columns
• Vertical columns
• Error Analysis

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Scattering Air Mass Factor Formulation (Palmer et
al.)
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Clear and Cloudy Scene Reflectivity (440 nm)
Toward the Nadir
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Spectral Fit

• Nonlinear least-squares inversion between 423-451
  nm
• Interfering species O3, O2-O2, and H2O
• Following Chance 1998 and Chance et al. 2000
  
• Direct fitting of radiance spectra
• Correction for spectral undersampling by the GOME
  instrument
• Wavelength calibration with a Fraunhofer
  reference spectrum
• Explicit treatment of the Ring effect
• Inclusion of a common mode spectrum
• Typical fitting precision 1.2x1015 molecules cm-2

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Error in the retrieval of tropospheric NO2
vertical columns
(1015 molecules cm-2)
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Conclusions

• We have developed an improved retrieval of
  tropospheric NO2 from GOME especially in the
  accounting for Rayleigh and cloud scattering
• GOME is more sensitive to NO2 columns over ocean
  than over land the assumption of zero NO2 over
  ocean would introduce a significant bias
• Fitting precision and AMF calculation are the
  dominant error sources

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Stratospheric Column Instrument Biases
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