Continuous Observational Data of Atmospheric CO2 Mixing Ratios on Hateruma Island

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The present data set is a set of continuous observational data of background CO2 mixing ratios in the vicinity of 20°N in the Western Pacific Ocean facing East Asia, measured on Hateruma Island, Okinawa Prefecture, Japan. Hateruma Island is a small island with a diameter of approx. 5 km. Because it is subjected to very small influence from local terrestrial ecosystem and/or anthropogenic CO2 emissions, the daily variations are small and the CO2 mixing ratios observed here can therefore be regarded as representative of the sub-tropics in the East Asian region. The Hateruma data reflects the influence from the Pacific Ocean in summer and from the Asian continent in winter, located downwind from each region, respectively.


Release date
Temporal coverage
1993/01/01 - 2022/12/31
Data provider
Email: cgerdb_admin(at)
File format
Data volume
Ver.1.5 (Last updated: 2023/06/30)

Data Set

CO2 mixing ratios
Time resolution
1 hour (60 minutes preceding the hour)
0.05 ppm
Observation period
From 1993 (ongoing)
24.06069°N, 123.80939°E
Elevation: 10m;
Sampling height:  37m above ground
Altitude: 47m
Measurement method
Air is sampled at a height of 37 m above ground by a sampling inlet mounted on a steel monitoring tower through a stainless tube to a ground-based observation room using a diaphragm pump. The sampled air is led into a measuring line where it goes through primary dehumidification at -45 °C and secondary dehumidification at -70 °C, after which the mixing ratios are determined using a measuring equipment (NDIR).
Every 3 hours, 4 cylinders of standard gases are measured and the CO2 mixing ratios are calibrated. Calibration of the standard gases is carried out using the NIES09 standard gas series developed by NIES.
Please refer to the webpage "GHGs Monitoring at Hateruma Island and Cape Ochi-ishi" for pictures of the measuring equipment.
Calculation method
First, CO2 mixing ratio values measured at 1-second intervals are averaged over 5 seconds, and then 12 such 5-second averages are averaged to produce an average mixing ratio value over a 1-minute period. The hourly values are then calculated by averaging all the 1-minute values in that hour.
The calibrated CO2 mixing ratio values are the time-weighted average values calculated from the calibration curve right before and after the measurements.
In Situ Land-based Platforms > GROUND STATIONS
Atmosphere > Atmospheric Chemistry > Carbon and Hydrocarbon Compounds > Carbon Dioxide
[Free keywords]
Greenhouse gases, carbon dioxide, CO2, global warming, Hateruma, continuous observations, infrared analyzer
Update history
A new data set for the period between November 2022 and December 2022 has been added. Ver.1.5.
A new data set of the period between October 2020 and October 2022 has been added. Supplementary dataset Ver.1.4 is identical to the previous version (Ver.1.2). Ver. 1.4.
A new data set of the CO2 measured by for the NDIR for the period between May 2020 and September 2021 has been added. Supplementary dataset Ver.1.3 is identical to the previous version (Ver.1.2). Ver. 1.3.
A new data set for the period between January 2014 and April 24, 2020 has been added. Since the CO2 data weren't often obtained due to the malfunction of the NDIR after December 2019, the CO2 data after December 2019 measured by a cavity ring-down spectroscopy (CRDS) analyzer have been added as a supplementary data set. Ver.1.2.
A new data set for the period between January 2011 and December 2013 has been added. The data between January 2008 and December 2013 have been corrected for biases. (The biases are arisen from a decrease in mixing ratios due to the use of copper pipes in the measurement equipment. The correction has been made using a function based on the difference with respect to the time series from bottled samples). The Conditions and Terms of Use have been revised as well. Ver.1.1.
The data from 1993 to 2010 have been compiled in NASA Ames Format 1001. Ver.1.0.


Project manager
Data manager
Shigeru Hashimoto (*1), Keiichi Katsumata (*1), Toshinobu Machida (*1), Noritsugu Tsuda(*2)
(*2) Global Environmental Forum

Reference Information

Supplementary data set
Zeng, JY, Nakajima, H., Matsunaga, T., Mukai, H., Hiraki, K., Yokota, Y. (2012), Linking Carbon Dioxide Variability at Hateruma Station to East Asia Emissions by Bayesian Inversion, Lagrangian Modeling of the Atmosphere (edited by Lin, J., Brunner, D., Gerbig, C., Stohl, A., Luhar, A., Webley, P.), Geophysical Monograph Series, 200, 163-172, doi:10.1029/2012GM001245.
Tohjima, Y., Mukai, H., Hashimoto, S., Patra, PK. (2010), Increasing synoptic scale variability in atmospheric CO2 at Hateruma Island associated with increasing East-Asian emissions, Atmos. Chem. Phys., 10, 453-462, doi:10.5194/acp-10-453-2010.
Mukai, H., Katsumoto, M., Ide, R., Machida, T., Fujinuma, Y., Nojiri,Y., Inagaki, M., Oda, N., Watai, T. (2001), Characterization of atmospheric CO2 observed at two-background air monitoring stations (Hateruma and Ochi-ishi) in Japan, Sixth International Carbon Dioxide Conference Extend Abstract, 1, 108-111, Organizing Committee of Sixth International Carbon Dioxide Conference, Sendai, Japan.

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When this data set is referred to in publications, it should, as a general rule, be made in the following format.
Mukai et al. (2014), Continuous observational data of atmospheric CO2 mixing ratios on Hateruma Island, Ver. x.x (*1), Center for Global Environmental Research, National Institute for Environmental Studies, DOI:10.17595/20160901.001. (Reference date: YYYY/MM/DD)(*2)
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