Technical note: Interferences of volatile organic compounds (VOCs) on methane concentration measurements

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Kohl , L , Koskinen , M , Rissanen , K , Haikarainen , I , Polvinen , T H , Hellén , H & Pihlatie , M 2019 , ' Technical note: Interferences of volatile organic compounds (VOCs) on methane concentration measurements ' , Biogeosciences , vol. 16 , no. 17 , pp. 3319-3332 . https://doi.org/10.5194/bg-16-3319-2019

Title: Technical note: Interferences of volatile organic compounds (VOCs) on methane concentration measurements
Author: Kohl, Lukas; Koskinen, Markku; Rissanen, Kaisa; Haikarainen, Iikka; Polvinen, Tatu Hannu; Hellén, Heidi; Pihlatie, Mari
Contributor: University of Helsinki, Department of Agricultural Sciences
University of Helsinki, Department of Agricultural Sciences
University of Helsinki, Ecosystem processes (INAR Forest Sciences)
University of Helsinki, Department of Agricultural Sciences
University of Helsinki, Department of Agricultural Sciences
University of Helsinki, Department of Agricultural Sciences
Date: 2019-09-04
Language: eng
Number of pages: 14
Belongs to series: Biogeosciences
ISSN: 1726-4170
URI: http://hdl.handle.net/10138/305844
Abstract: Studies that quantify plant methane (CH4) emission rely on the accurate measurement of small changes in the mixing ratio of CH4 that coincide with much larger changes in the mixing ratio of volatile organic compounds (VOCs). Here, we assessed whether 11 commonly occurring VOCs (e.g. methanol, α- and β-pinene, Δ3-carene) interfered with the quantitation of CH4 by five laser-absorption spectroscopy and Fourier-transformed infrared spectroscopy (FTIR) based CH4 analysers, and quantified the interference of seven compounds on three instruments. Our results showed minimal interference with laser-based analysers and underlined the importance of identifying and compensating for interferences with FTIR instruments. When VOCs were not included in the spectral library, they exerted a strong bias on FTIR-based instruments (64–1800 ppbv apparent CH4 ppmv−1 VOC). Minor (0.7–126 ppbv ppmv−1) interference with FTIR-based measurements were also detected when the spectrum of the interfering VOC was included in the library. In contrast, we detected only minor (<20 ppbv ppmv−1) and transient (< 1 min) VOC interferences on laser-absorption spectroscopy-based analysers. Overall, our results demonstrate that VOC interferences have only minor effects on CH4 flux measurements in soil chambers, but may severely impact stem and shoot flux measurements. Laser-absorption-based instruments are better suited for quantifying CH4 fluxes from plant leaves and stems than FTIR-based instruments; however, significant interferences in shoot chamber measurements could not be excluded for any of the tested instruments. Our results furthermore showed that FTIR can precisely quantify VOC mixing ratios and could therefore provide a method complementary to proton-transfer-reaction mass spectrometry (PTR-MS).
Subject: 219 Environmental biotechnology
1172 Environmental sciences
NITROUS-OXIDE EMISSIONS
SCOTS PINE
MONOTERPENE EMISSIONS
FOREST
CARBON
DEPENDENCE
PATTERNS
LIGHT
CH4
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