1Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, Mexico
2nstitute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Germany
Received: 24 Dec 2016 – Accepted: 09 Jan 2017 – Published: 11 Jan 2017
Abstract. In this investigation we analyze two common optical configurations to retrieve CO2 total column amounts from solar absorption infrared spectra. The noise errors using either a KBr or a CaF2 beamsplitter, a main component of a Fourier transform infrared (FTIR) spectrometer, are quantified in order to assess the relative precisions of the measurements. The configuration using a CaF2 beamsplitter, as deployed by the instruments which contribute to the Total Carbon Column Observing Network (TCCON), shows a slightly better precision. However, we show that the precisions in XCO2 retrieved from > 96 % of the spectra measured with a KBr beamsplitter, fall well below 0.2 %. A small bias in XCO2 (KBr – CaF2) of +0.56 ± 0.25 ppm was found when using an independent data set as reference. This value, which corresponds to +0.14 ± 0.064 %, is slightly larger than the mean precisions obtained and could be taken into account when homogenizing or comparing data from both beamsplitters. A 3-year XCO2 time series from FTIR measurements at the high-altitude site of Altzomoni in central Mexico presents clear annual and diurnal cycles and a trend of +2.2 ppm/yr could be determined.
Baylon, J. L., Stremme, W., Grutter, M., Hase, F., and Blumenstock, T.: Background CO2 levels and error analysis from ground-based solar absorption IR measurements in central Mexico, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-418, in review, 2017.
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