Measurement report: Method for evaluating CO2 emission from a cement plant by atmosphere O2/N2 and CO2 measurements and its applicability to the detection of CO2 capture signals.

Continuous observations of the atmospheric O₂/N₂ ratio and CO₂ amount fractions have been carried out at Ryori (RYO), Japan since August 2017. In these observations, the O₂:CO₂ exchange ratio (oxidative ratio (OR), -Δy(O₂)Δ y(CO₂)^-1) has frequently been lower than expected from short-term variations in emissions from terrestrial biospheric activities and combustion of liquid, gas, and solid fuels. This finding suggests a significant effect of CO₂ emission from a cement plant located about 6 km northwest of RYO. To evaluate this effect quantitatively, we simulated CO₂ amount fractions 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 amount fractions were converted to O₂ amount fractions by using the respective OR values for each of the incorporated CO₂ fluxes, and then simulated OR values were calculated from the calculated O₂ and CO₂ amount fractions. To extract the contribution of CO₂ emissions from the cement plant, we used y(CO₂*) as an indicator variable, where y(CO₂*) is a conservative variable for terrestrial biospheric activity and fossil fuel combustion obtained by simultaneous analyses of observed O₂/N₂ ratios and CO₂ amount fractions and simulated ORs. We confirmed that the observed and simulated OR values and also the y(CO₂*) values and simulated CO₂ amount fractions due only to cement production were generally consistent. These results suggest that combined measurements of O₂/N₂ ratios and CO₂ amount fractions 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. [ABSTRACT FROM AUTHOR]