Emissions of odorants following land application of livestock manure cause nuisance in the local environment for which reason odor legislation and abatement technologies are in demand. Collection of representative odor samples requires knowledge on emissions of odorants in the period following application of manure to soil or crop. In this work, the temporal evolution of odorant emissions is investigated based on laboratory scale dynamic chambers and field scale wind tunnels. Measurements of odorants have performed using proton-transfer-reaction mass spectrometry (PTR-MS), which is a sensitive analytical technique with sufficient time resolution for characterizing the temporal evolution of odorant emissions. It is observed that the most volatile and least water-soluble compounds, most notably H_2S, are only present in the initial few minutes following land application. In this initial stage, H_2S is assessed to contribute predominantly to odor based on its odor active value (OAV; concentration divided by odor threshold value). However, this contribution cease quickly within 10-20 minutes. The fast decay of emissions is well explained by the strong degree of partitioning of H_2S into the air phase. Sampling of this initial burst of odorant emission is very challenging due to the limited time available. At longer time scale, other odorants become more important, since they prevail and may be observed at levels above their odor threshold even on the next day following slurry application. The single compound that is estimated to contribute mostly to odor at longer time scales (based on OAV) is 4-methylphenol, but also 2,3-butanedione, trimethylamine and C5-carboxylic acids may be important. The implications for using olfactometry to measure odor from land-applied slurry are discussed.
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