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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. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

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 5000−20000ppmv 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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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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