Photoacoustic measurement with infrared band-pass filters significantly overestimates NH 3 emissions from cattle houses due to volatile organic compound (VOC) interferences
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.