Real‐time monitoring of carbon dioxide emissions from a shallow carbon dioxide release experiment

This study was conducted to analyze CO 2 migration from a shallow CO 2 release experiment using a continuous soil CO 2 flux measurement system. Approximately 1.8 t CO 2 was injected from 1 to 30 June 2016 through the point sources with perforated release wells laid at 2.5‐m soil depth. Using LI‐8100A instruments, CO 2 concentration, CO 2 flux, soil temperature, soil moisture, relative humidity, and atmospheric pressure were continuously measured every 30 min at 0, 1.5, 3.0, 4.5, and 6.0 m from the well from 29 May to 4 August 2016. Typically sensors for soil temperature and moisture were installed at 5‐cm depth, and CO 2 concentration, relative humidity, and atmospheric pressure were measured at the chambers. The CO 2 flux was not maximum directly above the release well. Carbon dioxide flux at 6.0 m from the well was similar to the background level. The relationship between CO 2 flux and environmental factors, described using a temporal correlation analysis, indicated that CO 2 flux was primarily driven by soil temperature and had the inverse correlation with relative humidity and atmospheric pressure. Heavy rainfall inhibited in‐soil CO 2 migration by filling the soil pore with water. The anomalously high CO 2 flux detected at 1.5 m from the well may have been caused by the associated permeability structure, in which a permeability discrepancy leads to the vertical or horizontal flow of in‐soil CO 2 . These findings from this shallow CO 2 release experiment should be considered as basic information to characterize and model the in‐soil CO 2 transport related to CO 2 leakage.