ALBERT

Description: A ground-based high resolution Fourier Transform Spectrometer (FTS) station has been established in Hefei, China to remotely measure CO2, CO and other trace gases based on near-infrared solar absorption spectra. Total columns of atmospheric CO2 and CO have been successfully measured from July 2014 to April 2016. Daily and monthly average column-averaged dry air mole fraction of CO2 showed a clear seasonal cycle, while the daily and monthly average of XCO displayed no seasonal variation. The spectra collected with an InSb detector in the first year were compared with those collected by an InGaAs detector from July 2015, demonstrating that InGaAs spectra have better signal-to-noise ratios and RMS spectral fitting residuals relative to InSb spectra. Consequently, the measurement precision of the retrieved XCO2 and XCO for InGaAs spectra is superior to InSb spectra, with about 0.04 % and 0.09 % for XCO2, 1.07 % and 2.00 % for XCO within clear sky days, respectively. We analyzed the relationship of daily average XCO2 and XCO on seasonal scale, found that although there was very weak correlation between them in summer and fall, there existed strong correlation in winter and spring. The CO2/CO correlation slope was 126.62 and 94.32 ppm/ppm in winter and spring for 2014–2015 and 2015–2016, respectively. The direct comparison of our observations with GOSAT data shows good agreement of daily average and monthly average XCO2, with biases of -0.64 ppm and -0.49 ppm, and standard deviations of 1.27 ppm and 1.12 ppm, respectively. The correlation coefficient (R2) is 0.87 and 0.92 for daily and monthly average XCO2 between our FTS and GOSAT observations, respectively. Daily average OCO-2 data produce a positive bias of 1.00 ppm and standard deviation of 1.92 ppm relative to our ground-based data, and the monthly average OCO-2 data give a bias of 1.07 ppm and standard deviation of 1.62 ppm. Our daily and monthly average XCO2 also show strong correlation with OCO-2 data, with correlation coefficient (R2) of 0.81 and 0.85, respectively. Although there were a limited number of data during the observations due to instrument failure and adverse weather, the results confirm the suitability of the observatory for long term measurements of greenhouse gases with high precision and accuracy.