Open AccessBased on Atmospheric Physics and Ecological Principle to Assess the Accuracies of Field CO 2 /H 2 O Measurements From Infrared Gas Analyzers in Closed‐Path Eddy‐Covariance Systems
Author(s) -
Zhou Xinhua,
Gao Tian,
Pang Yunchao,
Mahan Hayden,
Li Xiufen,
Zheng Ning,
Suyker Andrew E.,
Awada Tala,
Zhu Jiaojun
Publication year - 2021
Publication title -
earth and space science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.843
H-Index - 23
ISSN - 2333-5084
DOI - 10.1029/2021ea001763
Subject(s) - eddy covariance , covariance , range (aeronautics) , field (mathematics) , sensitivity (control systems) , span (engineering) , physics , meteorology , environmental science , mathematics , statistics , aerospace engineering , engineering , ecology , civil engineering , ecosystem , electronic engineering , pure mathematics , biology
Field CO 2 /H 2 O 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’ CO 2 /H 2 O accuracy equations. Based on atmospheric physics and environmental parameters, the analyzers are evaluated using the equations for CO 2 accuracy (±0.78 µmolCO 2 mol −1 , relatively ±0.18%) and H 2 O accuracy (±0.15 mmolH 2 O 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. H 2 O span needs more attentions under humid conditions. Under freezing conditions while H 2 O span is impractical, this span is fortunately unnecessary. Under the same conditions, H 2 O zero drift dominates H 2 O measurement uncertainty. Therefore, automatic zero becomes a more applicable and necessary tactic. In general cases of atmospheric CO 2 background, automatic CO 2 zero/span procedures can narrow CO 2 accuracy by 36% (±0.74 to ± 0.47 µmolCO 2 mol −1 ). Automatic/manual H 2 O zero/span procedures can narrow H 2 O accuracy by 27% (±0.15 to ±0.11 mmolH 2 O mol −1 ). While ensuring system specifications, the procedures guided by equations improve measurement accuracies.