Highly efficient colorimetric CO₂ sensors for monitoring CO₂ leakage from carbon capture and storage sites

Carbon capture and storage (CCS) technology used for reducing anthropogenic CO₂ emissions involves the capture of CO₂ from industrial sources and its injection into geological sinks, such as oil reservoirs and abandoned gas fields. To ensure environmental and public safety in implementing CCS technology, efficient CO₂-monitoring technology must be developed to detect potential CO₂ leakage from CCS sites. Conventional CO₂ sensors used for monitoring CCS sites are typically high in cost and require professional staff for maintenance. In this study, we developed a portable and low-cost colorimetric CO₂ sensor with high soil CO₂ detection efficiency for CCS sites. The sensor consists of a detection solution that contains the pH indicator cresol red encapsulated with a gas-permeable membrane. When CO₂ enters the sensor through the membrane, the color of the pH indicator changes and this was quantified using an RGB (red, green, blue) application (app), an app that measures the RGB values of a given color. The change in G and B values of the detection solution showed a significant linear relationship with soil CO₂ concentration determined via non-dispersive infra-red (NDIR) CO₂ sensor (r² = 0.98, p = 0.001), and thus these values were used for quantification of CO₂ concentration. Tests using CO₂-injection chamber showed that the optical CO₂ sensors can detect soil CO₂ concentration of 0.1 to 30% within a few minutes. Field studies conducted at a natural CO₂ vent and an artificial CO₂ leakage site showed that the optical CO₂ sensors can be applied in analyzing surficial CO₂ leakage patterns. The advantage of this optical CO₂ sensor when applied to field monitoring is that it is inexpensive and has few installation restrictions. Therefore, this optical CO₂ sensor has a strong potential for use in monitoring CO₂ leakages from CCS sites.