Characterization of VOC emissions from various components of dairy farming and their effect on San Joaquin Valley air quality

The San Joaquin Valley Air Basin in Central California is classified by the U.S. Environmental Protection Agency (EPA) as a serious non-attainment area for health-based eight-hour federal ozone (smog) standard (Lindberg, 2007). In August 2005, the San Joaquin Valley Air Pollution Control District issued a report identifying dairies as a main source of Volatile Organic Compounds (VOCs) and fine particulate matter in the valley (Crow, 2005). Among these compounds, we have found that ethanol, methanol, acetone and acetaldehyde are produced in major quantities throughout the San Joaquin valley as by-products of yeast fermentation of silage and photochemical oxidation. These oxygenates, especially ethanol, play an important role in ozone (O3) formation within the valley. Three different types of sampling protocols were employed in order to determine the degree of enhancement of the four oxygenates in the valley air shed, as well as to determine their sources, emission profiles and emission rates. An assessment of the emissions of these oxygenates in the valley was achieved using data obtained on low altitude flights through the valley and from ground level samples collected throughout the valley. By comparing the various ground and aircraft data, and ethanol emissions data obtained from silage, we were able to estimate the rate at which the air in the valley is ventilated to be between six and seven days. The photochemical production of ozone was calculated for each of the four oxygenates and approximately one hundred other quantified VOCs. Based on the Maximum Incremental Reactivity (MIR) scale and concentrations of each oxygenate in the atmosphere, as much as 20% of O3 production in the valley is from ethanol and its photochemical by-product acetaldehyde. Our findings suggest that improvement to the valley air quality may be obtained by focusing on instituting new silage containment practices and regulations.