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

Scattering Air Mass Factor Formulation (Palmer et al.)

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

AMF

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

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

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