Investigating the performance of a greenhouse gas observatory in Hefei, China

Abstract

Abstract. A ground-based high-resolution Fourier transform spectrometer (FTS) station has been established in Hefei, China to remotely measure CO 2 , CO and other greenhouse gases based on near-infrared solar absorption spectra. Total column measurements of atmospheric CO 2 and CO were successfully obtained from July 2014 to April 2016. 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 of spectral fitting residuals relative to InSb spectra. Consequently, the measurement precision of the retrieved XCO 2 and XCO for InGaAs spectra is superior to InSb spectra, with about 0.04 and 0.09 % for XCO 2 , and 1.07 and 2.00 % for XCO within clear-sky days respectively. Daily and monthly averages of columnaveraged dry air mole fraction of CO 2 show a clear seasonal cycle, while the daily and monthly averages of XCO displayed no seasonal variation. Also, we analysed the relationship of the anomalies of XCO and XCO 2 , found that the correlations are only observable for individual days, and the data under different prevailing wind conditions during the observations displayed weak correlation. The observations based on the high-resolution FTS were also compared with the temporally coinciding measurements taken with a low-resolution solar FTS instrument, the EM27/SUN. Ratioing the daily averaged XCO 2 of EM27 and FTS gives an overall calibration factor of 0.996 ± 0.001. We also compared ground-based observations from the Tsukuba TCCON station with our observations, the results showing that the variation in phase and seasonal amplitude of XCO 2 are similar to our results, but the variation of XCO in Tsukuba is quite different from our data in Hefei. To further evaluate our retrieved data, we made use of satellite measurements. The direct comparison of our observations with the Greenhouse Gases Observing Satellite (GOSAT) data shows good agreement of daily median XCO 2 , with a bias of −0.52 ppm and standard deviation of 1.63 ppm. The correlation coefficient (R 2 ) is 0.79 for daily median XCO 2 between our FTS and GOSAT observations. Daily median Orbiting Carbon Observatory 2 (OCO-2) data produce a positive bias of 0.81 ppm and standard deviation of 1.73 ppm relative to our ground-based data. Our daily median XCO 2 also show strong correlation with OCO-2 data, with correlation coefficient (R 2 ) of 0.83. Although there were a limited number of data during the observations due to instrument downtime and adverse weather, the results confirm the suitability of the observatory for ground-based long-term measurements of greenhouse gases with high precision and

Regional uncertainty of GOSAT XCO<sub>2</sub> retrievals in China: quantification and attribution

“…This obvious regional characteristic is most likely to relate to the assumption of a uniform cirrus profile based on latitude in the retrieval algorithm (GHG-CCI group at University of Leicester, 2014), which is, however, unlikely to be reasonable in our study area. A large amount of high clouds exist over the Tibetan Plateau (Chen et al, 2005), which is located south of the study cells 80 to 105 • E. The humidity and atmospheric structure of the study cells are consequently mainly affected by the Tibetan Plateau, and there is a large difference in the cirrus profile between the western cells and the eastern cells throughout our study area (Wang et al, 2012), which indicates that a uniform profile by latitude will inevitably introduce errors.…”

Analysis of CO<sub>2</sub> spatio-temporal variations in China using a weather–biosphere online coupled model

“…Our findings are consistent with recent measurements and inverse modelling studies but provide process-based estimates for anthropogenic emission and the terrestrial flux. Wu et al (2012) reported that measured CO 2 concentration at the Changbai Mountain forest site in northeast China increased by 1.76 ppmv yr −1 between 2003 and 2010. With the atmospheric inversion modelling method, Z. estimated that surface CO 2 in East Asia increased by 2-3 ppmv yr −1 between 2004 and 2012.…”

Ozone seasonal evolution and photochemical production regime in the polluted troposphere in eastern China derived from high-resolution Fourier transform spectrometry (FTS) observations

“…Human health, terrestrial ecosystems, and material degradation are impacted by poor air quality resulting from high photochemical ozone (O 3 ) levels (Wennberg and Dabdub, 2008;Edwards et al, 2013;Schroeder et al, 2017). In polluted areas, tropospheric O 3 is generated from a series of complex reactions in the presence of sunlight involving carbon monoxide (CO), nitrogen oxides (NO x ≡ NO (nitric oxide) + NO 2 (nitrogen dioxide)), and volatile organic compounds (VOCs) (Oltmans et al, 2006;Schroeder et al, 2017).…”