The Power of Online Proton Transfer Reaction - Mass Spectrometry (PTR-MS) Measurement of Odorous Emissions from a Pig House

Online monitoring of odorous compounds in the ventilation air was applied in an experimental pig house in Denmark. The measurements were executed by proton-transfer-reaction mass spectrometry (PTR-MS) while grab samples are used to confirm the identity of the compounds. Sorbent tubes samples were analysed by gas chromatography mass spectrometry analysis (GC-MS) and Tedlar bags samples by gas chromatography sulfur chemiluminescence detector (GC-SCD). For three target odorants, dimethyl sulfide, propanoic acid and p-cresol, the reproducibility after averaging over 1 hour was in the same order of magnitude for both grab and continuous sampling (<16 %). However, the detailed information on the concentration variations during the day provided by online measurements, can never be obtained by any analytic method requiring sample collection. The results emphasize the importance of a suitable strategy when taking grab samples for odour evaluation, for example for olfactometric measurements. Concentrations of odorants can easily differ by a factor of two within one week with similar weather circumstances and identical pigs.