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

Abstract. Studies that quantify plant methane (CH 4 ) emission rely on the accurate measurement of small changes CH 4 concentrations that coincide with much larger changes in the concentration of volatile organic compounds (VOCs). Here, we assessed if 11 commonly occurring VOCs (e.g., methanol, α- and β-pinene, ∆3-carene) interfered with CH 4 concentrations measurements by five laser absorption spectroscopy and Fourier-transformed infrared spectroscopy (FTIR) based CH 4 analysers, and quantified the interference of seven compounds on three instruments. Our results showed widespread interfere of 5 VOCs with FTIR based CH 4 analysers, but only minimal interference with laser absorption spectroscopy based analysers. VOCs not included in the spectral library exerted a strong strong (64–1800 ppb apparent CH 4 /ppm VOC) bias on FTIR based measurements, which can lead to substancial over- and underestimations of CH 4 fluxes. Minor (0.7–126 ppb/ppm) interferences with FTIR based measurements where also detected when the spectrum of the interfering VOC was included in the library. In contrast, we detected only minor ( 4 emissions. However, our results also suggest that FTIR can provided precisely quantify VOC concentrations, and could therefore provide a method complementary to proton-transfer-reaction mass spectrometry (PTR-MS).