[A-AS09] 大気化学

[AAS09-05] Evaluation of CO₂ emissions from a cement plant using atmospheric delta(O₂/N₂) and CO₂ measurements and its implication for future detection of CO₂ capture signals

*石戸谷 重之¹、坪井 一寛²、近藤 裕昭¹、石島 健太郎²、青木 伸行¹、松枝 秀和²、齊藤 和幸³ (1.産業技術総合研究所、2.気象研究所、3.気象庁)

キーワード：大気中O2/N2比、大気中CO2濃度、局所大気輸送モデル、セメント生産CO2排出

Continuous observations of atmospheric delta(O₂/N₂) and CO₂ concentrations have been carried out at Ryori (RYO), Japan since August 2017. In these observations, the O₂:CO₂ exchange ratio (OR, −DeltaO₂ / DeltaCO₂) has frequently been lower than those expected from short-term variations in emissions from terrestrial biospheric activities and fossil fuel combustion. This suggests a substantial effect of CO₂ emissions from a cement plant located about 6 km northwest of RYO. To evaluate this effect quantitatively, we simulated CO₂ concentration in the area around RYO by using a fine-scale atmospheric transport model that incorporated CO₂ fluxes from terrestrial biospheric activities, fossil fuel combustion, and cement production. The simulated CO₂ concentrations were converted to O₂ concentrations by using the respective OR values of 1.1, 1.4, and 0 for the terrestrial biospheric activities, fossil fuel combustion, and cement production. Thus obtained O₂ and CO₂ concentration changes were used to derive simulated OR for comparison with the observed OR. To extract the contribution of CO₂ emissions from the cement plant, we used an indicator closely related to atmospheric potential oxygen (APO = O₂ + 1.1×CO₂) but a conservative variable for terrestrial biospheric activities and fossil fuel combustion, obtained by simultaneous analysis of observed delta(O₂/N₂) and CO₂ concentrations and simulated ORs. We confirmed that the observed and simulated OR values and also the extracted and simulated CO₂ concentrations due to cement production were generally consistent. These results suggest that combined measurements of delta(O₂/N₂) and CO₂concentrations will be useful for evaluating CO₂ capture from flue gas at carbon capture and storage (CCS) plants, which, similar to a cement plant, change CO₂ amount fractions without changing O₂ values, although CCS plants differ from cement plants in the direction of CO₂ exchange with the atmosphere. These findings were reported by Ishidoya et al. (2024) recently, and we also show recent observational results of delta(O₂/N₂) and CO₂ concentrations at RYO in the presentation.

Acknowledgements
We acknowledge the many staff members of the Japan Meteorological Agency. This study was partly supported by JSPS KAKENHI (grant nos. 19H01975, 22H03739, and 22H05006) and the Global Environment Research Coordination System from the Ministry of the Environment, Japan (grant nos. METI1454 and METI1953)

Reference
Ishidoya, S., et al., Measurement report: Method for evaluating CO₂ emissions from a cement plant using atmospheric delta(O₂/N₂) and CO₂ measurements and its implication for future detection of CO₂ capture signals, Atmos. Chem. Phys., 24, 1059–1077, 2024.