Atmospheric radiocarbon (¹⁴C) and CO₂ mole fractions observed at Cape Ochiishi

Air samples have been collected every month since 2004 to observe background atmospheric ¹⁴CO₂. The air samples were drawn from the inlet by a diaphragm pump. The air was then passed through a cold trap (–45°C) and collected in Pyrex glass flasks equipped with two glass stopcocks sealed by Viton O-rings at 0.2 MPa in gauge pressure, after a 10-min purge. CO₂ mole fractions in the air samples were measured using a non-dispersive infrared gas analyzer (NDIR). CO₂ was extracted from the remaining whole air in the flask by passing it through a vacuum line. Water vapor was removed using a spiral trap cooled to –110 °C, and CO₂ was cryogenically trapped at –196 °C. The CO₂ samples were subsequently converted into graphite by reduction with hydrogen over an iron catalyst at 650 °C. The ¹⁴C/C ratios were measured using Compact Carbon AMS (CAMS, National Electrostatics Corp., 1.5SDH). Samples collected before 2013 were analyzed at Paleo Labo Co., Ltd., Japan and those collected after 2013 at NIES.

The ¹⁴CO₂ results were reported as Δ¹⁴C values relative to the OXII standard. Corrections were applied for radioactive decay between 1950 and the analysis date and mass-dependent fractionation using δ¹³C (normalized to −25‰) according to Stuiver and Polach (1977). Blank corrections were also applied. The Δ¹⁴C value and its uncertainty were calculated for each run, then final values were obtained by averaging repeated measurements. The analytical precision of Δ¹⁴C measurements (counting statistics and the standard deviation of OXII standards) was 2.1‰, ranging from 1.5‰ to 2.8‰. CO₂ mole fractions were determined against four working standard gases calibrated to the NIES 09 CO₂ standard scale (Machida et al., 2011). The analytical precision of CO₂ mole fractions (the average value of standard deviations for working standard gases) was ~0.02 ppm.

Platforms > Land-based Platforms > Permanent Land Sites >GROUND STATIONS

EARTH SCIENCE > ATMOSPHERE > ATMOSPHERIC CHEMISTRY > CARBON AND HYDROCARBON COMPOUNDS > ATMOSPHERIC CARBON DIOXIDE > CARBON DIOXIDE SURFACE

Carbon Cycle

The data from July 2004 to April 2021 have been compiled. Ver.1.0.

Yukio Terao (orcid.org/0000-0003-2345-7073)

Earth System Division, National Institute for Environmental Studies (NIES)

Hitoshi Mukai

Earth System Division, National Institute for Environmental Studies (NIES)

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

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