Measurement of Atmospheric NO₂ Column Density with Kitt Peak Solar Flux Atlas as a Reference

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The vertical column abundance of NO₂ is measured using direct sunlight. The solar spectra in the wavelength region of 430-450 nm observed from the earth's surface are ratioed with a reference spectrum taken from the Kitt Peak Solar Flux Atlas. The large Fraunhofer features (20-40%) are eliminated by wavelength correction, resolution matching and ratioing of observed spectra to the reference. The retrieved values of the NO₂ vertical column density are in a range of (2-15)×10¹⁶ molecules/cm² with an accuracy of better than 3%. This result demonstrates the usefulness of the Kitt Peak Atlas in the study of tropospheric NO₂ concentration, giving a standard extraterrestrial solar spectrum for the case in which the Langley method is not readily applicable.