|Mitlochner, Frank -|
Submitted to: Atmospheric Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 15, 2010
Publication Date: July 23, 2010
Citation: Hafner, S.D., Montes, F., Rotz, C.A., Mitloehner, F.M. 2010. Ethanol emission from loose corn silage and exposed silage particles. Atmospheric Environment. 44:4172-4180. Interpretive Summary: Smog is a widespread form of air pollution in the United States (US) and globally, and is recognized as a cause of premature death. Smog contains a mixture of pollutants that is usually quantified by measuring ozone gas, a dominant irritant in smog. Smog and ozone are created in the atmosphere when volatile organic compounds (VOCs) react with oxides of nitrogen (NOx). Reductions in VOC and NOx emissions from vehicles and industry over the past 40 years have resulted in a decline in ozone concentrations in the US. However, other sources of VOCs may be important in some areas. Recent measurements indicate that dairy farms may be a major source of VOCs in California. Measurements show that silage, a fermented cattle feed, and silage-containing mixed feed are the major sources of VOC emissions on dairy farms. However, the amount of VOCs emitted from dairy farms is not accurately known. In this work, we measured emission rates of ethanol (a dominant silage VOC) from loose corn silage. After exposure to moving air, ethanol emission rate declined drastically over time, showing that individual point estimates of emission rate are not sufficient. Emission rate and cumulative emission increased with air velocity, temperature, particle size, and exposed surface area. This work provides estimates of ethanol emission rates from silage on farms, and provides information that should be incorporated into procedures for measuring and modeling VOC emission from silage.
Technical Abstract: Silage and silage-containing feed on dairy farms have recently been identified as a source of volatile organic compound (VOC) emissions. In this work, we present measurements of ethanol (a dominant silage VOC) emission from loose corn silage samples made using a wind tunnel system. Flux of ethanol from bulk samples was highest immediately after exposing silage to moving air (as high as 220 g per square meter per hour) and declined by as much as 76-fold over 12 h as ethanol was depleted from the silage sample. Emission rate and cumulative 12 h emission increased with air velocity over the silage surface, silage temperature, particle size, and exposed surface area. Ethanol emission rates were found to be higher than previous estimates for bulk loose silage. For 15 cm deep bulk samples, approximately 80% of the initial ethanol was lost during 12 h of exposure to the highest air velocity (5 m per second). Emission rates measured with an emission isolation flux chamber were generally much lower than rates measured with either the wind tunnel or a mass balance of ethanol loss from silage exposed to moving air in an open setting. Results demonstrate that the emission isolation flux chamber method is not appropriate for estimating VOC emission rates from silage in the field.