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NARSTO Workshop on Innovative Methods for Emission Inventory Development and Evaluation University of Texas, Austin October 14-17, 2003 |
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Sesquiterpene Emissions And Secondary Organic Aerosol Formation Potentials For Southeast Texas
William Vizuete, Victoria Junquera, David T. Allen
Biogenic volatile organic compounds (BVOCs) emitted by vegetation include isoprene, monoterpenes (C10H16), and sesquiterpenes (C15H24). Sesquiterpene emissions account for approximately nine percent of the total biogenic emissions of non-methane hydrocarbons (NMHCs) in several forests in the United States. The importance of sesquiterpenes lies in their reactivity and potential for secondary organic aerosol formation (SOA). In southeast Texas experimental evidence was obtained during the summer of 2000 showing significant formation of biogenic SOA in the atmosphere. Radiocarbon (14C) analyses of fine particulate matter in air samples found a considerable fraction of 14C, or geologically modern carbon. The ratio of 14C/13C correlated strongly with the ratio of organic carbon to elemental carbon (OC/EC). This correlation suggested that the fraction of modern carbon in a sample is directly related to the amount of SOA and therefore that biogenic emissions may be a significant source of SOA precursors. The aims of this study are to estimate the sesquiterpene emissions from vegetation in southeast Texas and assess the potential contribution of these emissions to SOA formation. A modified version of the Global Biosphere Emissions and Interactions System (GloBEIS) was used to predict biogenic sesquiterpene emissions in the Houston-Galveston Area (HGA) in southeast Texas. The estimates were based on a land cover database containing more than 600 land cover categories at a resolution of approximately one kilometer and emission factors taken from literature. Average sesquiterpene emission fluxes were estimated to be between 0.07 and 0.65 kg Carbon/km2-hr. Fluxes at the lower end of the estimated range are consistent with observed concentrations of geologically modern carbon in Houston aerosol.