Modeling emissions of volatile organic compounds from silage

Volatile organic compounds (VOCs), a necessary reactant for photochemical smog formation, are emitted from numerous sources. Limited available data suggest that dairy farms emit VOCs with cattle feed, primarily silage, being the primary source. Process-based models of VOC transfer within and from silage during storage and feeding are presented. These models are based upon well-established theory for mass transport processes in porous media with parameters determined from silage properties using relationships developed for soils. Preliminary results indicate that VOC emission by advective flow of silage gas is generally insignificant compared to emission by surface convection and diffusion from within silage. VOC emissions are dependent upon silage properties, temperature, wind speed, and exposure duration, which have implications for measuring, predicting, and controlling VOC emissions from silage. Emissions appear to be co-limited by convection and diffusion; therefore, the EPA-style emission isolation flux chamber design previously used to measure VOC emissions from silage is not suitable for this task.