Continuous Observational Data of Atmospheric CH4 Mixing Ratios at Cape Ochi-ishi

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The present data set is time series data of atmospheric methane (CH4) mixing ratios measured at Cape Ochi-ishi situated at the base of Nemuro Peninsula in eastern Hokkaido, Japan. The monitoring station is located on top of a cliff 50 m above ground at the southern tip of the cape facing the Pacific Ocean. Air is sampled from an intake placed on a tower adjacent to the observation station about 50 m above ground level, and the CH4 mixing ratios are measured semi-continuously by using a gas chromatographic system. The winds tend to be predominantly northwesterly in winter and southwesterly in summer, whereas in spring and autumn no predominant wind direction has been observed. Because Hokkaido’s eastern part is dotted with swamps and grazing lands which are methane sources, and two cities, Nemuro and Kushiro are situated 20 km north and 100 km west, respectively, of the station, the influence from local methane emission sources is frequently observed.

Description

Supervisor
Release date
2016/09/01
Temporal coverage
1995/01/01 - 2015/12/31
Data provider
NIES
Email: cgerdb_admin(at)nies.go.jp
DOI
File format
Data volume
6.8MiB
Version
Ver.1.0 (Last updated: 2016/09/01)
Language
English

Data Set

Parameters
CH4 mixing ratios
Time resolution
1 hour (60 minutes preceding the hour)
Accuracy
2 ppb
Observation period
From 1995 (ongoing)
Location
43.1603°N, 145.4974°E
Altitude
Elevation: 42.5 m;
Sampling height: 51.5 m above ground
Measurement method
From an air intake placed on a steel monitoring tower 51.5 m above ground, outside air is drawn in through a stainless tube to a ground-based observation room using a diaphragm pump. A part of the sampled air is led into a Nafion® tube dryer and a cold trap at -40 °C to reduce water vapor in the sample air. Then the CH4 mixing ratio of the dried air sample is determined by a gas chromatograph equipped with a flame ionization detector (GC/FID).
Every 2 hours, 3 standard gases, which are CH4-in-air mixtures stored in high-pressure cylinders, are measured and calibration curves for the calculation of CH4 mixing ratios are determined. The CH4 mixing ratios of the standard gases is determined against the NIES94 standard scale developed by the National Institute for Environmental Studies (NIES). Please refer to the webpage "GHGs Monitoring at Hateruma Island and Cape Ochi-ishi" for pictures of the measuring equipment.
Calculation method
The basic GC cycle consists of 12 injections of 3 working standard gases with different CH4 mixing ratios followed by 9 air samples at 10-min intervals for each GC analysis. The atmospheric CH4 mixing ratios are determined by repeating this basic GC cycle. Every calibration curve for 9 consecutive air samples is determined by the 2 sets of the working standard gas analyses before and after the air sample analyses. The 1-hour value of methane mixing ratios is the mean mixing ratio of 3-6 air samples.
Keywords
[GCMD_Platform]
In Situ Land-based Platforms > GROUND STATIONS
[GCMD_Science]
Atmosphere > Atmospheric Chemistry > Carbon and Hydrocarbon Compounds > Methane
[Free keywords]
Greenhouse gases, methane, CH4, global warming, Ochi-ishi, continuous observations
Update history
[2016/09/01]
The data from 1995 to 2015 have been compiled in NASA Ames Format 1001. Ver.1.0.

References

References
Tohjima et al. (2002), Analysis and presentation of in situ atmospheric methane measurements from Cape Ochi-ishi and Hateruma Island, J. Geophys. Res., 107, 4148, DOI:10.1029/2001JD001003.

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Tohjima et al. (2002), Analysis and presentation of in situ atmospheric methane measurements from Cape Ochi-ishi and Hateruma Island, J. Geophys. Res., 107, 4148, DOI:10.1029/2001JD001003.
Tohjima et al. (2016), Continuous observational data of atmospheric CH4 mixing ratios at Cape Ochi-ishi, Ver. x.x (*1), Center for Global Environmental Research, National Institute for Environmental Studies, DOI:10.17595/20160901.004. (Reference date: YYYY/MM/DD)(*2)
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