Automated Near‐Continuous Measurement of Carbon Dioxide and Nitrous Oxide Fluxes from Soil

Abstract

AbstractTrace gas fluxes often show temporal variability on the order of hours and accurate quantification may be difficult without continuous or near‐continuous measurements. We developed an automated near‐continuous trace gas analysis system (NCTGAS) to measure soil‐atmosphere gas fluxes on a several‐times‐per‐day basis. In this system, air is circulated in a closed sample loop between fully automated flow‐through chambers and a photoacoustic infrared trace gas analyzer (TGA). The TGA quantifies infrared active gases at ambient levels within 2 to 3 min. We tested sensitivity, stability, and calibration of the TGA, and the ability of the NCTGAS to measure fluxes of CO2 and N2O. In addition to static tests, fluxes of CO2 and N2O were simulated by bleeding known quantities of these gases into a test chamber. Gas samples were simultaneously analyzed by TGA and removed for independent analysis of CO2 by conventional infrared gas analysis and for N2O by gas chromatography. The TGA‐based flux measurements were statistically identical to the independent measurements of both CO2 and N2O. In situ fluxes of CO2 and N2O measured by the NCTGAS were 105 ± 6 and 93 ± 10%, respectively, of those measured from hand‐drawn samples. The TGA was as or more stable than conventional means for measuring CO2 and N2O in air at ambient concentrations, and was equally sensitive across the range of concentrations normally encountered in field measurements. Fast response time and ease of use offers significant advantages over conventional gas chromatography.