Direct Sun measurements of NO_2 column abundances from Table Mountain, California: Intercomparison of low- and high-resolution spectrometers

Creators: Wang, Shuhui; Pongetti, Thomas J.; Sander, Stanley P.; Spinei, Elena; Mount, George H.; Cede, Alexander; Herman, Jay

Abstract

The NO_2 total column abundance, C_(NO_2) was measured with a direct Sun viewing technique using three different instruments at NASA Jet Propulsion Laboratory's (JPL) Table Mountain Facility in California during an instrument intercomparison campaign in July 2007. The instruments are a high‐resolution (∼0.001 nm) Fourier transform ultraviolet spectrometer (FTUVS) from JPL and two moderate‐resolution grating spectrometers, multifunction differential optical absorption spectroscopy (MF‐DOAS) (∼0.8 nm) from Washington State University and Pandora (∼0.4 nm) from NASA Goddard Space Flight Center. FTUVS uses high spectral resolution to determine the absolute NO_2 column abundance independently from the exoatmospheric solar irradiance using rovibrational NO_2 absorption lines. The NO_2 total column is retrieved after removing the solar background using Doppler‐shifted spectra from the east and west limbs of the Sun. The FTUVS measurements were used to validate the independently calibrated measurements of multifunction differential optical absorption spectroscopy (MF‐DOAS) and Pandora. The latter two instruments start with measured high‐Sun spectra as solar references to retrieve relative NO_2 columns and then apply modified Langley or "bootstrap" methods to determine the amounts of NO_2 in the references to obtain the absolute NO_2 columns. The calibration offset derived from the FTUVS measurements is consistent with the values derived from Langley and bootstrap calibration plots of the NO_2 slant column measured by the grating spectrometers. The calibrated total vertical column abundances of NO_2, C_(NO_2) from all three instruments are compared showing that MF‐DOAS and Pandora data agree well with each other, and both data sets agree with FTUVS data to within (1.5 ± 4.1)% and (6.0 ± 6.0)%, respectively.

Additional Information

© 2010 by the American Geophysical Union. Received 4 November 2009; revised 3 March 2010; accepted 10 March 2010; published 15 July 2010. We acknowledge the support of the NASA Upper Atmosphere Research and Aura Validation programs to each of these groups: JPL, WSU, and GSFC. We also wish to thank the staff at JPL's Table Mountain Facility, especially Pam Glatfelter and Bruce Williamson, for their exceptional support during the intercomparison campaign. The WSU group thanks Robert Gibson for help in the field. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology; Washington State University; and the Goddard Space Flight Center under contract to the National Aeronautics and Space Administration.