The Atmospheric Chemistry of n-, i-, s- and t-butanol biofuels
Speaker: Max McGillan, NOAA ESRL CSD & CU CIRES
When: Wednesday, September 25, 2013, 3:30 p.m. Mountain Time
Location: Room 2A305, DSRC (NOAA Building), 325 Broadway, Boulder
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Butanol (C4H9OH) is a potential biofuel alternative to fossil fuel gasoline formulations. The usage of butanol would lead to direct emissions into the atmosphere. Reaction with the OH radical is expected to be the predominant atmospheric removal process for all four butanol isomers. The environmental impact of butanol emissions was assessed by determining both the rate with which it reacts with OH and the product branching ratios associated with this reaction – these branching ratios are of particular importance since the relative abundance of product functionality (mostly ketones and aldehydes) will largely determine the effects on air quality. Absolute rate coefficients for the gas-phase reaction of n-, i-, s-, and t-butanol with OH were measured using the pulsed laser photolysis–laser induced fluorescence technique over the temperature range 221–381 K. Previous measurements of these rate coefficients are available, but are of insufficient precision to observe the non-Arrhenius behavior observed in this work. This non-Arrhenius behavior is used to interpret the competition between the available H-atom abstraction reactive sites, which have different activation energies and pre-exponential factors. Further laboratory work will also be presented, using a static environmental chamber apparatus to determine stable end product branching ratios. The present results are analyzed in conjunction with combustion-temperature kinetic studies, product studies and structure-activity relationships (SARs) to derive a series of self-consistent site-specific reaction rate coefficients for use in atmospheric and combustion chemistry modeling.