title: Improved membrane-based sensor network for reliable gas monitoring in the subsurface.
abstract: A conceptually improved sensor network to monitor the partial pressure of CO(2) in different soil horizons was designed. Consisting of five membrane-based linear sensors (line-sensors) each with 10 m length, the set-up enables us to integrate over the locally fluctuating CO(2) concentrations (typically lower 5%(vol)) up to the meter-scale gaining valuable concentration means with a repetition time of about 1 min. Preparatory tests in the laboratory resulted in a unexpected highly increased accuracy of better than 0.03%(vol) with respect to the previously published 0.08%(vol). Thereby, the statistical uncertainties (standard deviations) of the line-sensors and the reference sensor (nondispersive infrared  CO(2)-sensor) were close to each other. Whereas the uncertainty of the reference increases with the measurement value, the line-sensors show an inverse uncertainty trend resulting in a comparatively enhanced accuracy for concentrations >1%(vol). Furthermore, a method for in situ maintenance was developed, enabling a proof of sensor quality and its effective calibration without demounting the line-sensors from the soil which would disturb the established structures and ongoing processes.
authors.affiliation: Helmholtz-Centre for Environmental Research, T.-Lieser-Strasse 4, 06120 Halle, Germany. detlef.lazik@ufz.de
authors.forename: Detlef
authors.initials: D
authors.lastname: Lazik
authors.forename: Sebastian
authors.initials: S
authors.lastname: Ebert
mesh_terms: D002245:Carbon Dioxide / Q000302:isolation & purification*; D004784:Environmental Monitoring; D005740:Gases / Q000302:isolation & purification*; D006801:Humans; D012987:Soil / Q000737:chemistry
chemical_list: D005740:Gases; D012987:Soil; D002245:Carbon Dioxide