Investigating the performance of a greenhouse gas observatory in Hefei, China
A ground-based high-resolution Fourier transform spectrometer (FTS) station has been established in Hefei, China to remotely measure CO<sub>2</sub>, CO and other greenhouse gases based on near-infrared solar absorption spectra. Total column measurements of atmospheric CO<sub>2&l...
Main Authors: | , , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-07-01
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Series: | Atmospheric Measurement Techniques |
Online Access: | https://www.atmos-meas-tech.net/10/2627/2017/amt-10-2627-2017.pdf |
Summary: | A ground-based high-resolution Fourier transform spectrometer (FTS)
station has been established in Hefei, China to remotely measure CO<sub>2</sub>, CO
and other greenhouse gases based on near-infrared solar absorption spectra.
Total column measurements of atmospheric CO<sub>2</sub> 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<sub>2</sub> and XCO for InGaAs spectra is superior to InSb spectra, with about
0.04 and 0.09 % for XCO<sub>2</sub>, and 1.07 and 2.00 % for XCO within
clear-sky days respectively. Daily and monthly averages of column-averaged dry
air mole fraction of CO<sub>2</sub> 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<sub>2</sub>, 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<sub>2</sub> 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<sub>2</sub> 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<sub>2</sub>, with a bias of −0.52 ppm and standard deviation of 1.63 ppm. The correlation coefficient (<i>R</i><sup>2</sup>) is 0.79 for daily median
XCO<sub>2</sub> 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<sub>2</sub> also show strong correlation with
OCO-2 data, with correlation coefficient (<i>R</i><sup>2</sup>) 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 accuracy, and fulfil the requirements of the Total Carbon
Column Observing Network (TCCON). |
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ISSN: | 1867-1381 1867-8548 |