Daily Observational Data of Atmospheric CO2 Mixing Ratios at the Summit of Mt. Fuji

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The present data set is a set of daily observational data of background CO2 mixing ratios in midlatitude Asian region, measured at the summit of Mt. Fuji which is the highest mountain in Japan (3776 m a.s.l.) and located in the middle of mainland Japan. Its summit is located in the free troposphere which means it is not affected directly by air at ground level for most of the year. The daily variations of CO2 mixing ratio was not observed and CO2 mixing ratios of Mt. Fuji and aircraft measurement near Mt. Fuji were in good agreement. Therefore, they suggested that the data at the summit of Mt. Fuji could be considered representative of the free-tropospheric CO2 mixing ratio in the midlatitude Asian Region.


Release date
Temporal coverage
2009/07/21 - 2022/08/22
Data provider
Email: cgerdb_admin(at)nies.go.jp
File format
Data volume
380 KB
Ver.2.0(Last updated: 2022/12/09)

Data Set

CO2 mixing ratios
Time resolution
1 day
0.05 ppm
Observation period
From 2009 (ongoing)
35.3609°N, 138.7271°E
Elevation: 3776 m;
Sampling height: 4 m above ground
Air is sampled at a height of 4 m above ground by a sampling inlet mounted on a water tank which is located next to the building of Mt. Fuji weather station through polytetrafluoroethylene tube to the station room using an air pump. The sampled air is led into a measuring line where it goes through a drying system using a membrane, silica gel of 2000 mL, after which the mixing ratios are determined using a measuring equipment (NDIR).
Because of the limited power supply during winter, the measurement was configured to operate for only about 1.5 h per day. We selected the time period 15:00-16:28 Japan Standard Time (JST) from July 2009 to July 2010. However, we changed the period to 22:00-23:28 JST since August 2010. At 22:00 (or 15:00), room air is introduced into NDIR for 2 minutes. Then outside air is measured for 8 minutes. Next, three working standard gases are measured for 4 minutes each to calibrate the measurement. Generally, this sequence is repeated four times. Calibration of the standard gases is carried out using the NIES09 standard gas series developed by NIES.
Calculation method
The daily values of CO2 mixing ratio was based on the average of the data from the second (time period for the measurement: 22:24-22:32), third (22:46-22:54), and fourth cycles (23:08-23:16); in other words, the daily data is based on 3 x 6 min (because we discarded the first 2 min data for 8 min data) = 18 minutes of observations. The calibrated CO2 mixing ratio values are the time-weighted average values calculated from the calibration curve right before and after the measurements.
[Free keywords]
Carbon Dioxide, CO2, Mt. Fuji, Japan, Asia, Free Troposphere, Mountain Site
In Situ Land-based Platforms > Ground Stations
Atmosphere > Atmospheric Chemistry > Carbon Dioxide
Update history
The data from 2009 to 2022 have been compiled, the sampling height modified 5 m to 4m and the project manager changed Dr Yukio Terao. Ver. 2.0.
The data from 2009 to 2019 have been compiled in NASA Ames Format 1001. Ver.1.1.
The data from 2009 to 2016 have been compiled in NASA Ames Format 1001. Ver.1.0.


Shohei Nomura, Hitoshi Mukai, Yukio Terao, Toshinobu Machida and Yukihiro Nojiri (2017), Six years of atmospheric CO2 observations at Mt. Fuji recorded with a battery-powered measurement system. Atmospheric Measurement Techniques, 10, 667-680, doi:10.5194/amt-10-667-2017.

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Nomura et al. (2017), Daily observational data of atmospheric CO2 mixing ratios at the summit of Mt. Fuji, Ver.x.x *1, Earth System Division, NIES, DOI:10.17595/20170616.001, (Reference date*2: YYYY/MM/DD)
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