Measurement report: Method for evaluating CO2 emissions from a cement plant using atmospheric δ(O2/ N2) and CO2 measurements and its implication for future detection of CO2 capture signals.

Continuous observations of atmospheric δ(O2/N2) and CO 2 amount fractions have been carried out at Ryori (RYO), Japan, since August 2017. In these observations, the O 2 : CO 2 exchange ratio (ER, -Δy(O2)Δy(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 substantial effect of CO 2 emissions from a cement plant located about 6 km northwest of RYO. To evaluate this effect quantitatively, we simulated CO 2 amount fractions in the area around RYO by using a fine-scale atmospheric transport model that incorporated CO 2 fluxes from terrestrial biospheric activities, fossil fuel combustion, and cement production. The simulated CO 2 amount fractions were converted to O 2 amount fractions by using the respective ER values of 1.1, 1.4, and 0 for the terrestrial biospheric activities, fossil fuel combustion, and cement production. Thus obtained O 2 and CO 2 amount fraction changes were used to derive a simulated ER for comparison with the observed ER. To extract the contribution of CO 2 emissions from the cement plant, we used y(CO2∗) as an indicator variable, where y(CO2∗) is a conservative variable for terrestrial biospheric activities and fossil fuel combustion obtained by simultaneous analysis of observed δ(O2/N2) and CO 2 amount fractions and simulated ERs. We confirmed that the observed and simulated ER values and also the y(CO2∗) values and simulated CO 2 amount fractions due only to cement production were generally consistent. These results suggest that combined measurements of δ(O2/N2) and CO 2 amount fractions will be useful for evaluating CO 2 capture from flue gas at carbon capture and storage (CCS) plants, which, similar to a cement plant, change CO 2 amount fractions without changing O 2 values, although CCS plants differ from cement plants in the direction of CO 2 exchange with the atmosphere. [ABSTRACT FROM AUTHOR]