AuthorsMizoguchi, Y., Ohtani, Y.
TitleComparison of Response Characteristics of Small CO2 Sensors and an Improved Method Based on the Sensor Response
JournalJournal of agricultural meteorology
KeywordsCO2 sensor, diffusion, flow-through, nonlinear regression, response time
AbstractPortable infrared CO2 sensors, such as GMT222 (VAISALA) and LI-820 (LI-COR), are often used for soil CO2 efflux measurements; however, in general, these inexpensive small sensors are relatively inaccurate and slow to respond. The output signals are delayed as a result of diffusion processes in the sample cell and internal averaging calculations to ensure stable data output. Accurate estimations of CO2 efflux require calculating the actual increase in CO2 concentration in a chamber without these composite delays.
Laboratory experiments were conducted to determine the response characteristics of several sensors under two different conditions: diffusion and flow-through. The data obtained in the experiments indicated that attachment of a dust filter substantially delayed the sensor response. Furthermore, the sensor response time under the diffusion condition was longer than under the flow-through condition. When the soil CO2 efflux was calculated using a nonlinear regression method, a long response time led to large CO2 efflux estimation errors; for example, a 10% underestimation occurred when CO2 concentrations were measured using GMM222C with a sampling interval of 300 seconds. We developed a backward estimation method for recovering the actual increase in CO2 concentration from the delayed sensor outputs. Correction of the sensor response with the backward estimation provides an effective solution for achieving an accurate estimation of the soil CO2 efflux using inexpensive sensors.