Carbon dioxide retrievals from Atmospheric Chemistry Experiment solar occultation measurements

Abstract

The Atmospheric Chemistry Experiment (ACE) satellite (SCISAT-1) was launched into an inclined orbit on 12 August 2003 and is now recording high signal-to-noise 0.02 cm -1 resolution solar absorption spectra covering 750-4400 cm -1 (2.3-13 μm). A procedure has been developed for retrieving average dry air CO 2 mole fractions (X CO2) in the altitude range 7-10 km from the SCISAT-1 spectra. Using the N 2 continuum absorption in a window region near 2500 cm -1, altitude shifts are applied to the tangent heights retrieved in version 2.2 SCISAT-1 processing, while cloudy or aerosol-impacted measurements are eliminated. Monthly mean X CO2 covering 60°S to 60°N latitude for February 2004 to March 2008 has been analyzed with consistent trends inferred in both hemispheres. The ACE X CO 2 time series have been compared with previously reported surface network measurements, predictions based on upper tropospheric aircraft measurements, and space-based measurements. The retrieved X CO 2 from the ACE-FTS spectra are higher on average by a factor of 1.07 ± 0.025 in the Northern Hemisphere and by a factor of 1.09 ± 0.019 on average in the Southern Hemisphere compared to surface station measurements covering the same time span. The ACE-derived trend is ∼0.2% per year higher than measured at surface stations during the same observation period. Copyright 2010 by the American Geophysical Union.