Atmospheric CO₂ retrieved from ground‐based near IR solar spectra

Abstract

The column‐averaged volume mixing ratio (VMR) of CO 2 over Kitt Peak, Arizona, has been retrieved from high‐resolution solar absorption spectra obtained with the Fourier transform spectrometer on the McMath telescope. Simultaneous column measurements of CO 2 at ∼6300 cm −1 and O 2 at ∼7900 cm −1 were ratioed to minimize systematic errors. These column ratios were then scaled by the mean O 2 VMR (0.2095) to yield column‐averaged vmrs of CO 2 . These display similar behavior to the Mauna Loa in situ surface measurements. During the period 1977–1995, the column‐averaged mixing ratio of CO 2 increased at an average rate of 1.49 ± 0.04 ppmv/yr with seasonal variations of ∼7 ppmv peak‐to‐peak. Our retrievals demonstrate that this remote technique is capable of precisions better than 0.5%.