Temperature and air velocity effects on ethanol emission from corn silage with the characteristics of an exposed silo face Felipe Montes a, * , Sasha D. Hafner a , C. Alan Rotz a , Frank M. Mitloehner b a USDA-Agricultural Research Service, Building 3702, Curtin Road, University Park, PA 16082-3702, USA b Department of Animal Science, University of California, Davis, CA 95616, USA article info Article history: Received 17 November 2009 Received in revised form 24 February 2010 Accepted 26 February 2010 Keywords: Volatile organic compounds Ethanol Ozone precursor Silage Farm emissions abstract Volatile organic compounds (VOCs) from agricultural sources are believed to be an important contributor to tropospheric ozone in some locations. Recent research suggests that silage is a major source of VOCs emitted from agriculture, but only limited data exist on silage emissions. Ethanol is the most abundant VOC emitted from corn silage; therefore, ethanol was used as a representative compound to characterize the pattern of emission over time and to quantify the effect of air velocity and temperature on emission rate. Ethanol emission was measured from corn silage samples removed intact from a bunker silo. Emission rate was monitored over 12 h for a range in air velocity (0.05, 0.5, and 5 m s 1 ) and temperature (5, 20, and 35  C) using a wind tunnel system. Ethanol flux ranged from 0.47 to 210 g m 2 h 1 and 12 h cumulative emission ranged from 8.5 to 260 g m 2 . Ethanol flux was highly dependent on exposure time, declining rapidly over the first hour and then continuing to decline more slowly over the duration of the 12 h trials. The 12 h cumulative emission increased by a factor of three with a 30  C increase in temperature and by a factor of nine with a 100-fold increase in air velocity. Effects of air velocity, temperature, and air-filled porosity were generally consistent with a conceptual model of VOC emission from silage. Exposure duration, temperature, and air velocity should be taken into consideration when measuring emission rates of VOCs from silage, so emission rate data obtained from studies that utilize low air flow methods are not likely representative of field conditions. Published by Elsevier Ltd. 1. Introduction Troposphere ozone is a widespread air pollution problem and cause of premature death in the USA ((US Environmental Protection Agency) EPA, 2008; National Research Council, 2008; Jerrett et al., 2009). Decreases in emissions of volatile organic compounds (VOCs) and oxides of nitrogen, both reactants for tropospheric ozone formation, have been effective in reducing ozone concen- trations over the past 40 years (EPA, 2003). In the US, VOC emis- sions from on-road vehicles and industrial sources (which account for approximately 75% of anthropogenic VOC emissions) have been significantly reduced, resulting in a 50% decline in total anthropo- genic emissions since 1970 (EPA, 2003, 2009a,b). These sources may not be the most important sources in all regions, however. Recently, agriculture has been implicated as a source of VOCs in California. Most of California's San Joaquin Valleydan area with high concentration of large dairy farmsdis classified as an ozone nonattainment area by the EPA (EPA, 2009c) and the San Joaquin Air Pollution Control Board reports that agriculture is the largest single emitter of VOCs (San Joaquin Valley Air Pollution Control District, 2008). Many VOCs have been detected on dairy farms, including alco- hols, acids, aldehydes, ketones, and esters (Alanis et al., 2008; Shaw et al., 2007; Filipy et al., 2006; Hobbs et al., 2004; Ngwabie et al., 2008; Rabaud et al., 2003; Sunesson et al., 2001). Few studies have measured VOC emission rates from isolated sources on dairy farms, but those that have demonstrate that silage and silage- containing total mixed rations (TMR) are together the largest source of VOC emissions (Card and Schmidt, 2006; Alanis et al., 2008; Chung et al., 2009). Card and Schmidt (Card and Schmidt, 2006; Schmidt, 2006) used an emission isolation flux chamber to measure VOC flux from six different sources on two California dairy farms. Measured fluxes from silage and TMR were more than an order of magnitude greater than fluxes from manure sources. Although the exposed area of silage and TMR is much smaller than that of other sources, the estimated contribution of silage was close to 50% of total farm VOC emissions for one farm and greater than 80% for the other. Chung et al. (2009) used a similar flux chamber * Corresponding author. Tel.: þ1 814 863 0942; fax: þ1 814 863 0935. E-mail address: felipe.montes@ars.usda.gov (F. Montes). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Published by Elsevier Ltd. doi:10.1016/j.atmosenv.2010.02.037 Atmospheric Environment 44 (2010) 1987e1995