Photoacoustic measurement with infrared band-pass filters significantly overestimates NH&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; emissions from cattle houses due to volatile organic compound (VOC) interferences

Dezhao Liu,Li Rong,Xianwang Kong,Albarune Chowdhury,Jesper Kamp,Anders Feilberg,Anders Peter S Adamsen

doi:10.5194/amt-13-259-2020

Abstract

Abstract. Infrared (IR) photoacoustic spectroscopy (PAS) using band-pass filters is a widely used method for measurement of NH3 and greenhouse gas emissions (CH4, N2O and CO2) especially in agriculture, but non-targeted gases such as volatile organic compounds (VOCs) from cattle barns may interfere with target gases, causing inaccurate results. This study made an estimation of NH3 interference in PAS caused by selected non-targeted VOCs which were simultaneously measured by a PAS and a PTR-MS (proton-transfer-reaction mass spectrometry). Laboratory calibrations were performed for NH3 measurement, and VOCs were selected based on a headspace test of the feeding material (maize silage). Strong interferences of VOCs were observed on NH3 and greenhouse emissions measured by PAS. Particularly, ethanol, methanol, 1-butanol, 1-propanol and acetic acid were found to have the highest interferences on NH3, giving empirical relationships in the range of 0.7 to 3.3 ppmv NH3 per ppmv VOC. A linear response was typically obtained, except for a nonlinear relation for VOCs on N2O concentration. The corrected online NH3 concentrations measured by PAS in a dairy farm (with empirical relationships 2.1±0.8 and 2.9±1.9 for Location 1 and Location 2, respectively) were confirmed to be correlated (R2=0.73 and 0.79) to the NH3 concentration measured simultaneously by the PTR-MS when the empirical corrections obtained from single VOC tests were applied.

Highlights

Measurements of ammonia and greenhouse gas (CH4, N2O and CO2) emissions are gaining increasing attention due to stronger interest in global change and air pollution
The instrumental baseline concentrations of ammonia-free zero air measured by photoacoustic spectroscopy (PAS), cavity ring-down spectroscopy (CRDS) and proton-transferreaction mass spectrometry (PTR-MS), respectively, are shown in Fig. 2a, in which a very low background signal was observed for the CRDS instrument with a detection limit of 0.7 ppbv (3 times the standard deviation of the background)
For the calibration test of ammonia, the ammonia concentrations simultaneously measured by the CRDS and the PTR-MS are shown in Fig. 2b, in which the linearity (k = 0.96±0.005) and high correlation (R2 = 0.999) are generally very satisfactory for both instruments

Summary

Introduction

Measurements of ammonia and greenhouse gas (CH4, N2O and CO2) emissions are gaining increasing attention due to stronger interest in global change and air pollution. Greenhouse gas emissions, on the other hand, cause climate change (Thomas et al, 2004; Chadwick et al, 2011). In the USA, agriculture accounts for ∼ 90 % of the total ammonia emissions (Aneja et al, 2009). Agriculture accounts for 52 % and 84 % of global anthropogenic methane and nitrous oxide emissions (Smith et al, 2008). Accurate measurements of ammonia and greenhouse emissions are vital for reliable emission estimation and thereby for the possible reduction of these emissions through various efforts, such as air cleaning with biotrickling filters and air scrubbers (Melse and Van der Werf, 2005; De Vries and Melse, 2017). More than a 30 % difference between different methods has been reported (Scholtens et al, 2004)

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Conclusion