Impacts of Dairies and Silage on Air Quality

Ground-level ozone formation continues to be a critical problem in the United States. The problem is especially severe in California, generally, and Central California’s San Joaquin Valley (SJV), specifically. Dairies are one of the major sources of volatile organic compounds (VOCs) in SJV and have recently attracted considerable attention from the regulatory agencies. A number of recently conducted studies have reported actual emissions data from different dairy sources. However, there is currently limited data available for feed storage and silage piles, which are potentially significant contributors to ozone formation. The impact of different VOCs on ozone formation varies significantly from one species to another. Comprehensive measurements of VOC emissions are required to fully characterize and include all the important contributors to atmospheric reactivity. Therefore, the identification of emitted VOCs is needed to properly assess the wide spectrum of chemicals involved in ozone formation. This research study aims to identify and quantify the VOCs emitted from various silages and other feed sources. We have conducted experiments in an environmental chamber using large representative samples under controlled conditions. Over eighty VOCs were identified and quantified from corn, alfalfa, and cereal silages, total mixed rations, almond shells, and almond hulls using gas chromatography-mass spectrometry (GC/MS). Emissions of aldehyde compounds and acetone were measured using high performance liquid chromatography (HPLC). The results revealed high fluxes of alcohols and other oxygenated species. Lower, but perhaps comparably significant, concentrations of highly reactive alkenes and aldehydes were also detected. Additional quantitation and monitoring of these emissions are essential for assessment of and response to the specific needs of the regional air quality in the SJV.