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United States Department of Agriculture

Agricultural Research Service

Research Project: Assessing Atmospheric Emissions from Concentrated Animal Feeding Operations in the Pacific Northwest

Location: Northwest Irrigation and Soils Research

Title: Increasing the quantitative credibility of open-path FT-IR spectroscopic data with focus on several properties of the background spectrum

Authors
item Shao, Limin -
item Wang, Wanping -
item Griffiths, Peter -
item Leytem, April

Submitted to: Journal of Applied Spectroscopy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 7, 2012
Publication Date: March 1, 2013
Citation: Shao, L., Wang, W., Griffiths, P.R., Leytem, A.B. 2013. Increasing the quantitative credibility of open-path FT-IR spectroscopic data with focus on several properties of the background spectrum. Journal of Applied Spectroscopy. 67(3):335-341.

Interpretive Summary: Open-path Fourier transform infrared (OP/FT-IR) spectrometry can be used to measure gaseous emissions from agricultural operations. However, quantification of gases can be a difficult and complex task. The choice of the type of background spectrum affects the credibility of OP/FT-IR spectroscopic data, and consequently the quality of data analysis. We systematically investigated several properties of the background spectrum. The results show that a short-path background measured with the lowest amplifier gain could significantly reduce noise in the calculated absorbance spectrum, by at least 30% in our case. We demonstrated that by using a short-path background, data analysis is more resistant to interferences, such as wavenumber shift or resolution alteration that occurs as a consequence of hardware aging or misalignment. We also discussed a systematic error introduced into quantitative analyses by the short-path background, and developed a procedure to correct the error. With this correction approach, a short-path background measured five years ago was still found to be valid. By incorporating these findings into the protocol for quantitative analysis, we processed the measurements by two OP/FT-IR instruments set up side by side in the vicinity of a large dairy farm to monitor NH3, CH4 and N2O. The two sets of calculated concentrations showed high agreement with each other. The findings of our investigations are helpful to atmospheric monitoring practi-tioners of OP/FT-IR spectroscopy and could also be a reference for future amendment to the protocols outlined in the guidelines of the US Environmental Protection Agency (USEPA), the American Society for Testing and Materials (ASTM), and the European Committee for Stand-ardization (ECS).

Technical Abstract: The choice of the type of background spectrum affects the credibility of open-path Fourier transform infrared (OP/FT-IR) spectroscopic data, and consequently the quality of data analysis. We systematically investigated several properties of the background spectrum. The results show that a short-path background measured with the lowest amplifier gain could significantly reduce noise in the calculated absorbance spectrum, by at least 30% in our case. We demonstrated that by using a short-path background, data analysis is more resistant to interferences, such as wavenumber shift or resolution alteration that occurs as a consequence of hardware aging or misalignment. We also discussed a systematic error introduced into quantitative analyses by the short-path background, and developed a procedure to correct the error. With this correction approach, a short-path background measured five years ago was still found to be valid. By incorporating these findings into the protocol for quantitative analysis, we processed the measurements by two OP/FT-IR instruments set up side by side in the vicinity of a large dairy farm to monitor NH3, CH4 and N2O. The two sets of calculated concentrations showed high agreement with each other. The findings of our investigations are helpful to atmospheric monitoring practitioners of OP/FT-IR spectroscopy and could also be a reference for future amendment to the protocols outlined in the guidelines of the US Environmental Protection Agency (USEPA), the American Society for Testing and Materials (ASTM), and the European Committee for Standardization (ECS).

Last Modified: 12/18/2014
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