Based on Atmospheric Physics and Ecological Principle to Assess the Accuracies of Field CO2/H2O Measurements From Infrared Gas Analyzers in Closed-Path Eddy-Covariance Systems

Xinhua Zhou, Tian Gao, Yunchao Pang, Hayden Mahan, Xiufen Li, Ning Zheng, Andrew E. Suyker, Tala Awada, Jiaojun Zhu

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Field CO2/H2O measurements from infrared gas analyzers in closed-path eddy-covariance systems have wide applications in earth sciences. Knowledge about exactness of these measurements is required to assess measurement applicability. Although the analyzers are specified with uncertainty components (zero drift, gain drift, cross-sensitivities, and precision), exactness for individual measurements is unavailable due to an absence of methodology to comprehend the components as an overall uncertainty. Adopting an advanced definition of accuracy as a range of all measurement uncertainty sources, the specified components are composited into a model formulated for studying analyzers’ CO2/H2O accuracy equations. Based on atmospheric physics and environmental parameters, the analyzers are evaluated using the equations for CO2 accuracy (±0.78 µmolCO2 mol−1, relatively ±0.18%) and H2O accuracy (±0.15 mmolH2O mol−1). Evaluation shows that precision and cross-sensitivity are minor uncertainties while zero and gain drifts are major uncertainties. Both drifts need adjusting through zero/span procedures during field maintenance. The equations provide rationales to guide and assess the procedures. H2O span needs more attentions under humid conditions. Under freezing conditions while H2O span is impractical, this span is fortunately unnecessary. Under the same conditions, H2O zero drift dominates H2O measurement uncertainty. Therefore, automatic zero becomes a more applicable and necessary tactic. In general cases of atmospheric CO2 background, automatic CO2 zero/span procedures can narrow CO2 accuracy by 36% (±0.74 to ± 0.47 µmolCO2 mol−1). Automatic/manual H2O zero/span procedures can narrow H2O accuracy by 27% (±0.15 to ±0.11 mmolH2O mol−1). While ensuring system specifications, the procedures guided by equations improve measurement accuracies.

Original languageEnglish (US)
Article numbere2021EA001763
JournalEarth and Space Science
Volume8
Issue number10
DOIs
StatePublished - Oct 2021
Externally publishedYes

ASJC Scopus subject areas

  • Environmental Science (miscellaneous)
  • Earth and Planetary Sciences(all)

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