Atmospheric CH4 and N2O data from the flask air sampling over Surgut

Motoki Sasakawa ^*1 (orcid.org/0000-0003-2273-5131),Toshinobu Machida ^*1
*1Earth System Division, National Institute for Environmental Studies (NIES)

2024/01/16

1993/07/23 - 2021/12/26

NIES
Email: cgerdb_admin(at)nies.go.jp

514 KB

ver.1.0 (Last updated: 2024/01/16)

English

From Jul. 23rd, 1993 (ongoing)

Vertical: 0.5 - 7.0 km

Air sampling was carried out approximately once per month using a chartered aircraft (AN-24) at the altitudes of 7.0, 5.5, 4.0, 3.0, 2.0, 1.5, 1.0, and 0.5 km within a 130 km distance from Surgut International Airport (61°20′36″ N, 73°24′12″ E). Since 21 April 2018, the flight was made from a different airfield (61°23′26″ N, 73°12′18″ E) using a Cessna aircraft. Air was sampled upwind of Surgut to avoid direct contamination from the city. Two samples were collected at each altitude during the level flight, and the sampling interval was 2–3 min. It took 40–50 min to collect all samples from 7.0 to 0.5 km. Flights were performed around noon or in the afternoon of local time. The air sample was introduced into the cockpit through an inlet placed in front of the engine exhaust and pressurized into a Pyrex glass flask at about +0.2 MPa over cabin pressure by using an electric diaphragm pump (MOA-P101-JH or DOA-P501, GAST Manufacturing Inc.). The stopcocks of the glass flasks and the diaphragm pump were operated manually.
Until February 2005, the air samples were sent to Tohoku University and analyzed for CH₄ concentration using a gas chromatograph equipped with a flame ionization detector (GC-FID). The GC systems used were a GC-9A (Shimadzu Corp.) in earlier years and an Agilent 6890 (Agilent Technologies, Inc.) since November 2002. Each gas sample was analyzed once or twice. Repetitive calibrations using multiple CH₄ standard gas mixtures indicated that the repeatability of our measurements was 3 ppb for the GC-9A and 2 ppb for the Agilent 6890 system (Umezawa et al., 2014). The CH₄ concentration was determined against the TU scale (Aoki et al., 1992), which is ~3.2 ppb higher than the WMO-CH₄-X2004 scale in the concentration range of 1755.5–1820.2 ppb (Round Robin Comparison Experiment; http://www.esrl.noaa.gov/gmd/ccgg/wmorr/).
The N₂O concentrations of the air samples were determined using a GC equipped with an electron capture detector (ECD) at Tohoku University. Two sets of GC systems were used; one is GC-14A (Shimazu, Japan) for the sample obtained until September 2002, and Agilent 6890 (Agilent Technologies, USA) for the sample obtained after October 2002. The precision was 1 ppb for GC-14A and 0.2 ppb for Agilent 6890. The working standard gases were calibrated against the gravimetrically prepared primary standard gases (Machida et al., 1995).
After March 2005, the air samples were sent to NIES and analyzed for CH₄ concentration using GC-FID. The system used was HP5890 (Hewlett-Packard Comp.) until April 2014, followed by Agilent 7890A (Agilent Technologies, Inc.) for the samples collected after 24 April 2014. Each gas sample was analyzed three times if possible. The repeatability of the measurements was 1.3 ppb and 0.9 ppb based on the repeated measurements of dry cylinder air. The concentration was determined against the NIES 94 CH₄ scale, which is ~3.7 ppb higher than the WMO-CH₄-X2004 scale in the concentration range of 1755.5–1820.2 ppb (Round Robin Comparison Experiment). Both the TU and NIES scales showed good agreement in their precision.
The N₂O measurements at NIES were done by Agilent 6890 with an ECD for the sample obtained until 24 November 2011 and µECD from 28 December 2011. The precision was 0.18 ppb for the ECD and 0.43 ppb for the µECD based on the repeated measurements of dry cylinder air. The working standard gases were calibrated against the NIES 96 N₂O scale.
[References]
Aoki, S., T. Nakazawa, S. Murayama, and S. Kawaguchi (1992), Measurements of atmospheric methane at the Japanese Antarctic Station, Syowa, Tellus B, 44(4), 273-281, doi:10.3402/tellusb.v44i4.15455.
Machida, T., T. Nakazawa, Y. Fujii, S. Aoki, and O. Watanabe (1995), Increase in the atmospheric nitrous oxide concentration during the last 250 years, Geophys. Res. Lett., 22(21), 2921-2924, doi:10.1029/95GL02822.
Umezawa, T., D. Goto, S. Aoki, K. Ishijima, P. K. Patra, S. Sugawara, S. Morimoto, and T. Nakazawa (2014), Variations of tropospheric methane over Japan during 1988–2010, Tellus B, 66(0), doi:10.3402/tellusb.v66.23837.

The average value is described for samples with multiple measurements; the analysis value is expressed as is for samples with a single measurement. For the samples measured repeatedly, we set a criterion that the standard deviation (SD) of repeated measurements of less than two times the precision was valid (dependent on the GC systems); that is, we did not show the CH₄ data whose SD was more significant than 2.6 ppb for the period from March 2005 to January 2014, and 1.8 ppb from April 2014 to December 2021. As for N₂O, 0.36 ppb from March 2005 to November 2011 and 0.86 ppb from December 2011 to December 2021. In the measurement at Tohoku University, at most, two analyses were performed, so if the difference between the two analysis values exceeded four times the repeatability, the instrument was considered unstable, and we did not show the values.

[Free keywords]

[2024/01/16]

Miyuki Yanai
National Institute for Environmental Studies (NIES)

Kentaro Ishijima ^*1, Shinji Morimoto ^*2
*1 Meteorological Research Institute (MRI)
^*2 Tohoku University

Sasakawa, M., T. Machida, K. Ishijima, M. Arshinov, P. K. Patra, A. Ito, S. Aoki, and V. Petrov (2017), Temporal Characteristics of CH₄ Vertical Profiles Observed in the West Siberian Lowland Over Surgut From 1993 to 2015 and Novosibirsk From 1997 to 2015, Journal of Geophysical Research-Atmospheres, 122(20), 11261-11273, doi:10.1002/2017jd026836.

The observations were supported by a fund for global environmental monitoring by CGER, NIES.

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