Retrieval of Atmospheric COand CHVariations Using Ground-Based High Resolution Fourier Transform Infrared Spectra

Abstract

High resolution Fourier transform near IR solar spectra are used to estimate the column-averaged dry-air mole fraction (DMF) of COand CH 4 variations in the atmosphere. The preliminary retrieval results for COand CH 4 variations in the area of Hefei, China, are presented, and the underlying error sources are also analyzed. Both a forward analysis and an inversion algorithm are included in the retrieval. The forward analysis uses the modeled atmospheric transmittance to line-by-line (LBL) convolute the instrument line shape function. The influences of the temperature, pressure, humidity, and a priori gases are considered in the atmospheric transmittance model. The inversion algorithm is based on the nonlinear iterative and nonlinear least squares spectral fitting, which is used to obtain VC D CO 2 and VC D CH 4 (which represent vertical column density of COand CH 4, resp.). Furthermore, the VC D O 2 is also retrieved for converting the VCDs into DMFs. DMFs are final products of data analysis. The inversion results can clearly resolve the tiny variations of COand CH 4 under strong atmospheric background. Spectral fitting residuals for both VC D CO 2 and VC D CH 4 are less than 0.5%. Finally, COand CH 4 diurnal variations are investigated based on a typical observation. About 2 ppm amplitude for DMF C O 2 diurnal variations and less than 15 ppb amplitude for D MF CH 4 are observed.