Volume 5, Issue 7 (July 2008)
Assessment of the Ozone Formation Potential from Pesticide Solvents Using a Mobile Ozone Chamber Assay Approach
The use of pesticides in California’s agricultural industry plays a role in air quality with emissions of organic compounds thought to contribute to the formation of ground level ozone. Ozone levels in many regions of California exceed the prescribed Federal and State standards every year. The actual contribution from pesticide applications (as well as other agricultural sources) is largely unknown, and relies on assumptions of reactivity and tendency to evaporate. Progress on accurate determinations of either parameter is limited by many factors, including the proprietary nature of formulations. We have developed an approach which can measure the ozone formation potential of many agricultural sources, in the field. This approach was previously validated and described during a recently completed and published study of emissions from dairy cattle, their feed, as well as their fresh waste. With accompanying measurements of the most abundant volatile organic compounds (VOCs) involved there, we showed agreement between laboratory studies, field measurements, and a computer model of atmospheric photochemical reactions that improves upon past efforts, which were limited to urban/industrial VOCs. Our goal is to reach the same level of understanding for VOCs contained in pesticide formulations.
Two sets of field experiments were performed to assess the ozone formation potential of pesticide solvents using a set of transportable smog chambers in the summer of 2007. The first set of experiments were conducted for a solvent-based emulsifiable concentrate (EC) base-spray on a one-acre bare field, and the second set of experiments were conducted for an agricultural application of Lorsban 4E in a three-acre citrus orchard. By comparing the upwind and downwind measurements, the experiments indicated that the emission of pesticide solvent after field application led to increased ozone formation. After a 180 min UV exposure, the ozone formation potential measured at the downwind side averaged 14 ppb higher than that of upwind air, while the average difference was around 3 ppb for background levels on both the day before and the day after pesticide spray. Laboratory experiments were also conducted for different doses of EC base with various levels of nitrogen oxides using the transportable smog chambers. The experimental isopleth demonstrates that VOCs emitted from the EC base could result in high ozone formation. Future work will provide full VOC speciation and application of the results in a regional photochemical model to predict ozone impacts.