Retrieval of vertical profiles and tropospheric CO columns based on high-resolution FTIR over Hefei, China.

High-resolution solar absorption spectra, observed by ground-based Fourier Transform Infrared spectroscopy (FTIR), are used to retrieve vertical profiles and partial or total column concentrations of many trace gases. In this study, we present the tropospheric CO columns retrieved by mid-infrared solar spectra over Hefei, China. To reduce the influence of stratospheric CO cross-dependencies on tropospheric CO, an a posteriori optimization method based on a simple matrix multiplication is used to correct the tropospheric CO profiles and columns. The corrected tropospheric CO time series show an obvious annual increase and seasonal variation. The tropospheric CO annual increase rate is 2.71 ± 0.36 ppm yr, with the annual peak value in January, and CO decreases to a minimum in August. Further, the corrected tropospheric CO from GEOS-Chem simulations are in good agreement with the coincident FTIR data, with a correlation coefficient between GEOS-chem model and FTS of 0.89. The annual increase rate of XCO observed from near-infrared solar absorption spectra is in good agreement with the tropospheric CO but the annual seasonal amplitude of XCO is only about 1/3 of dry-air averaged mole fractions (DMF) of tropospheric CO. This is mostly attributed to the seasonal variation of CO being mainly dominated by sources near the surface.