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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/amt-2018-373
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2018-373
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Dec 2018

Research article | 07 Dec 2018

Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Measurement Techniques (AMT) and is expected to appear here in due course.

Application of Open Path Fourier Transform Infrared Spectroscopy (OP-FTIR) to Measure Greenhouse Gas Concentrations from Agricultural Soils

Cheng-Hsien Lin1, Cliff T. Johnston1, Richard H. Grant1, and Albert J. Heber2 Cheng-Hsien Lin et al.
  • 1Department of Agronomy, Purdue University, West Lafayette, IN 47907, United States
  • 2Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, IN 47907, United States

Abstract. Open-path Fourier transform infrared spectroscopy (OP-FTIR) has often been used to measure hazardous or trace gases from the "hot" point sources (e.g., volcano, industrial or agricultural facilities) but seldom used in the field-scale source areas, such as soil emissions. OP-FTIR, the close-path mid-IR laser-based N2O, and the nondispersive-IR CO2 analyzers were used to measure the concentrations of greenhouse gases (e.g., N2O and CO2) emitted from agricultural soils over a period of 9−19 June in 2014. We developed a quantitative method of N2O/CO2 analysis that minimized the interferences from diurnal changes of humidity and temperature in order to measure N2O/CO2 concentrations accurately. Two chemometric multivariate models were developed, a classical least squares (CLS) and a partial least squares (PLS), respectively. This study evaluated different methods to generate the single beam background spectra, and different spectral regions to determine N2O/CO2 concentrations from OP-FTIR spectra. A standard extractive method was used to measure the "actual" path-averaged concentrations along an OP-FTIR optical path in situ, as a benchmark to assess the feasibilities of these quantitative methods. Within the absolute humidity of 5000−20 000 ppmv and the temperature of 10−35 °C, we found that the CLS model underestimated N2O concentrations (Bias = −4.9 ± 3.1 %) calculated from OP-FTIR spectra, and the PLS model improved the accuracy of the calculated N2O (Bias = 1.4 ± 2.3 %). The bias of the calculated CO2 was −1.0 ± 2.8 % using the CLS model. These methods suggested that the changed ambient factors potentially led to biases in N2O/CO2 estimations from OP-FTIR spectra, and may help the OP-FTIR user to escape from the dependency of extractive methods used to calibrate the concentration determined by OP-FTIR.

Cheng-Hsien Lin et al.
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Interactive discussion
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Status: closed
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Cheng-Hsien Lin et al.
Cheng-Hsien Lin et al.
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Short summary
The open path FTIR (OP-FTIR) is often used to measure the atmospheric gas composition and concentrations. The OP-FTIR, however, is sensitive to the changed ambient factors, which likely led to quantitative biases. This study developed methods to minimize the effect of the ambient temperature and humidity on N2O/CO2 quantification. These methods can help the increased users who implement the OP-FTIR to estimate gas fluxes in the agroecosystem achieve more precise and accurate estimations.
The open path FTIR (OP-FTIR) is often used to measure the atmospheric gas composition and...
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