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

Abstract

This study was conducted to analyze CO2 migration from a shallow CO2 release experiment using a continuous soil CO2 flux measurement system. Approximately 1.8 t CO2 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, CO2 concentration, CO2 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 CO2 concentration, relative humidity, and atmospheric pressure were measured at the chambers. The CO2 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 CO2 flux and environmental factors, described using a temporal correlation analysis, indicated that CO2 flux was primarily driven by soil temperature and had the inverse correlation with relative humidity and atmospheric pressure. Heavy rainfall inhibited in-soil CO2 migration by filling the soil pore with water. The anomalously high CO2 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 CO2. These findings from this shallow CO2 release experiment should be considered as basic information to characterize and model the in-soil CO2 transport related to CO2 leakage.