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Data Description GGG2009

TCCON Dry Column-Averaged Mixing Ratios of CO2, CO, N2O, CH4 and H2O

Version: GGG2009. The archived GGG2009 data can be found on the GGG2009 Archive. The most recent data are described on the main Data Description page.

CONTENTS

INTRODUCTION

Column-average Dry Mole Fractions (DMF) reported in this database were acquired using a Fourier Transform Spectrometer (FTS). Direct solar spectra
were acquired in the near-infrared spectral region. These spectra were used to retrieve column abundances of CO2, O2, CH4, N2O, H2O.

GENERAL COMMENTS ON THE DATA

Dry column-average Gas G DMF has been calculated according to

Column CO2 is retrieved for two CO2 bands centered at 6228 cm-1 and 6348 cm-1. The average of the two calculated CO2 DMFs is presented here.

Column O2 is retrieved from the electronic band centered at 7882 cm-1.

Column CH4 is retrieved for three CH4 bands centered at 5938 cm-1, 6002 cm-1 and 6076 cm-1. The average is presented here.

Column N2O is retrieved for bands centered at 4389 cm-1 and 4429 cm-1.

Column CO is retrieved for bands centered at 4233 cm-1 and 4290 cm-1.

Column H2O is retrieved from bands centered at 6076, 6177, 6392, 6099, 6255, 6401, 6125, 6301 and 6469 cm-1.

Sources of Error

The dry column-averaged DMF () is affected by three main sources of error:

Measurement precision (repeatability)

The TCCON measurement precision is <0.25% under clear or partly cloudy skies (up to 5% fractional variation in solar intensity), and solar zenith angles <82 degrees.

Spectroscopic errors

The retrieved O2 columns were NOT reduced by 2.27% to bring them into agreement with the dry surface pressure, as described in Washenfelder et al. (2006). The absolute accuracy of the retrievals was calibrated by comparison to integrated aircraft profiles, resulting in the corrections listed below. The aircraft profiles were performed with the sun at lower airmasses, and the column-average DMF are now well-calibrated for these values. However, additional systematic errors may be present at higher airmass due to errors in the spectroscopy of the gas of interest and/or O2.

Systematic instrumental changes over time

There are known drifts in these instruments, and care is taken to minimize and correct for these errors.

Data Comparisons

TCCON data should be compared with other data using the Rodgers and Connor (2003) approach. Column averaging kernels and a priori profiles are available either on the Auxiliary Data page or from the individual principal investigators.

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CORRECTIONS AND CALIBRATIONS

The data are corrected for airmass-dependent and airmass-independent (in situ) errors. These correction factors are applied to the column-averaged
mole fractions.

The former (ADCF) is determined offline from the symmetric component of the diurnal variation. The latter (AICF) is determined offline by comparisons
with in situ profiles measured over TCCON sites with aircraft equipped with WMO-standard instrumentation.

Gas ADCF AICF AICF Error (2sigma)
xco2 -0.0075 0.989 0.002
xch4 0.0000 0.978 0.004
xn2o 0.0000 0.958 0.01
xco 0.0000 0.98 0.04
xh2o 0.0000 1.03 0.1

The airmass-dependent calibration is described in the supplementary material to:

Wunch, D., G. C. Toon, J.-F. L. Blavier, R. A. Washenfelder, J. Notholt, B. J. Connor, D. W. T. Griffith, V. Sherlock, P. O. Wennberg. The Total Carbon
Column Observing Network, doi: 10.1098/rsta.2010.0240 Phil. Trans. R. Soc. A 28 May 2011 vol. 369 no. 1943 2087-2112

The in situ calibration factors were developed and described in:

Wunch, D., Toon, G. C., Wennberg, P. O., Wofsy, S. C., Stephens, B. B., Fischer, M. L., Uchino, O., Abshire, J. B., Bernath, P., Biraud, S. C.,
Blavier, J.-F. L., Boone, C., Bowman, K. P., Browell, E. V., Campos, T., Connor, B. J., Daube, B. C., Deutscher, N. M., Diao, M., Elkins, J. W.,
Gerbig, C., Gottlieb, E., Griffith, D. W. T., Hurst, D. F., Jimenez, R., Keppel-Aleks, G., Kort, E. A., Macatangay, R., Machida, T., Matsueda, H.,
Moore, F., Morino, I., Park, S., Robinson, J., Roehl, C. M., Sawa, Y., Sherlock, V., Sweeney, C., Tanaka, T., and Zondlo, M. A.: Calibration of the
Total Carbon Column Observing Network using aircraft profile data, Atmos. Meas. Tech., 3, 1351-1362, doi:10.5194/amt-3-1351-2010, 2010.

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SITE-SPECIFIC NOTES

Lamont

The wind speed and direction sensor was faulty until March 26, 2009. It is possible that the wind speed values prior to March 26, 2009 are valid but noisy, but the wind direction values are not. All values since March 26, 2009 are valid.

The spectroscopic line list used to process the Lamont data changed on November 2, 2009. The data processed on that date and after are higher by ~0.5 ppm in XCO2. The newer line list is better, but unfortunately does not match with the line list used by the other TCCON sites.

New laser detector boards and laser were installed on April 14, 2011 to eliminate the effect of mis-sampling ('ghosts'). The magnitude of the change has not yet been quantified, but it is likely <1 ppm in XCO2.

Lauder

Please refer to the official output file header information (ascii files) for the two Lauder FTS instruments attached below

Tsukuba

The bias for the Tsukuba data measured with an old FTS (Bruker IFS 120 HR) using the 2010 aircraft calibration campaign over Tsukuba was estimated. We did three overpasses and a bias for the Tsukuba FTS value obtained with the TCCON common data processing is -1.32 ppm +/- 0.46 ppm (1 sigma) for XCO2. The 1.32 ppm bias was added to these XCO2 data.

A bias for XCH4 likely exists but its magnitude has not yet been estimated.
 

Reference: Tanaka, T. et al.: The 2010 Aircraft Calibration Campaign over Tsukuba, Japan, in preparation, 2011. 

Park Falls

New laser detector boards were installed on June 23, 2011 to eliminate the effect of mis-sampling ('ghosts'). The magnitude of the change has not yet been quantified, but it is likely <1 ppm in XCO2.

Bialystok

XCO2

Prior to September 27, 2009, a laser sampling error ('ghosts') caused a bias in XCO2. On this date, the bias was minimized, and the magnitude of the effect quantified as being 0.96 ppm in XCO2. Originally, it was inferred that this bias resulted in an XCO2 that was too high before the ghost minimization, and therefore XCO2 before September 27, 2009 was reduced by 0.96 ppm. However more recent evidence suggests that this correction was in fact in the wrong direction.

On September 30, 2011, new data were uploaded to the TCCON data archive, where the XCO2 before September 27, 2009 was corrected by +0.96 ppm. 

XCH4

In the original release of Bialystok data to the TCCON data archive it was later discovered that one of the XCH4 microwindows had not been retrieved for ~3 months early in the Bialystok timeseries. Due to the relative biases between the microwindows, this resulted in an underestimate of XCH4 of ~10 ppb. This was rectified in the July 2011 data release.

Izana

For measurements from 2007-2010 the O2-column is affected by ghosts. On September 23, 2011, new data with a preliminary ghost-correction (based on the ratio O2-column/pressureground) was uploaded to the TCCON data archive.

 

Bremen

The next release (post- October 2011) of Bremen data will feature an update to the pressure associated with some of the spectra. This is due to a correction implemented to account for the height difference between the pressure measured at the instrument, and that measured at Bremen airport. The Bremen airport meteorological data are used in the case where no in situ data are available at the time of the spectrum. This mostly affects the earliest data, and occasional spectra at other times. The affect of this on the retrievals has not yet been quantified, but the pressure difference is generally ~3hPa, with the correction resulting in a decreased pressure (the instrument is at a higher altitude than the airport).

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