This proposal addresses biosphere-atmosphere exchange of acetone, a volatile organic compound (VOC) that enters the Earth's atmosphere and is important in odd hydrogen radical (HOx) and background ozone formation in the upper troposphere and lower stratosphere. Acetone photochemistry also results in the formation of peroxyacetylnitrate, with resultant sequestering and transport of odd nitrogen (NOx) equivalents. While it is clear that these acetone-related processes affect the oxidative capacity of the atmosphere, there are significant uncertainties in the global acetone budget, estimated as 40-60 Tg yr-1, especially in the rates of biogenic acetone emission and the mechanisms of biogenic acetone formation. The major goal of the proposed work is to establish the underlying mechanisms of formation of acetone and methyl ethyl ketone in plant tissues, and to characterize the controls over their release from plant surfaces. We also want to determine if certain crops have been overlooked as major sources of carbonyl emissions. The project will include both laboratory experiments and field verification via examination of data sets from collaborative field experiments organized by scientists at the National Center for Atmospheric Research (NCAR). Planned laboratory, greenhouse and field experiments should produce much-needed data sets on biogenic carbonyl fluxes from vegetation, and should contribute to the development of an integrated plant VOC emission model to explain the partitioning of plant carbon into volatiles. This modeling could be significant, because plants often emit 1-8% of fixed CO2 as VOCs, and an important aspect of biosphere-atmosphere exchange is to understand why and how plants commit resources to volatile secondary compound production. Such information is vital if we are to predict changes that will occur in the Earth's atmosphere as the result of human impacts of the biosphere.
