1. 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

2. Scattering Air Mass Factor Formulation (Palmer et al.)

5. Clear and Cloudy Scene Reflectivity (440 nm) Toward the Nadir

6. AMF

7. 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

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

13. 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

14. THE NEXT SLIDES ARE EXTRA

16. Stratospheric Column & Instrument Biases