title: New insights to the use of ethanol in automotive fuels: a stable isotopic tracer for fossil- and bio-fuel combustion inputs to the atmosphere.
abstract: Ethanol is currently receiving increased attention because of its use as a biofuel or fuel additive and because of its influence on air quality. We used stable isotopic ratio measurements of (13)C/(12)C in ethanol emitted from vehicles and a small group of tropical plants to establish ethanol's δ(13)C end-member signatures. Ethanol emitted in exhaust is distinctly different from that emitted by tropical plants and can serve as a unique stable isotopic tracer for transportation-related inputs to the atmosphere. Ethanol's unique isotopic signature in fuel is related to corn, a C4 plant and the primary source of ethanol in the U.S. We estimated a kinetic isotope effect (KIE) for ethanol's oxidative loss in the atmosphere and used previous assumptions with respect to the fractionation that may occur during wet and dry deposition. A small number of interpretive model calculations were used for source apportionment of ethanol and to understand the associated effects resulting from atmospheric removal. The models incorporated our end-member signatures and ambient measurements of ethanol, known or estimated source strengths and removal magnitudes, and estimated KIEs associated with atmospheric removal processes for ethanol. We compared transportation-related ethanol signatures to those from biogenic sources and used a set of ambient measurements to apportion each source contribution in Miami, Florida-a moderately polluted, but well ventilated urban location.
authors.affiliation: University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, Florida 33149, United States. bgiebel@rsmas.miami.edu
authors.forename: Brian M
authors.initials: BM
authors.lastname: Giebel
authors.forename: Peter K
authors.initials: PK
authors.lastname: Swart
authors.forename: Daniel D
authors.initials: DD
authors.lastname: Riemer
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D001336:Automobiles; D056804:Biofuels / Q000032:analysis*; D002247:Carbon Isotopes; D005591:Chemical Fractionation; D000431:Ethanol / Q000032:analysis*; D005431:Florida; D005579:Fossil Fuels / Q000032:analysis*; D007553:Isotope Labeling / Q000379:methods*; D010084:Oxidation-Reduction; D010944:Plants / Q000378:metabolism; D001335:Vehicle Emissions / Q000032:analysis
chemical_list: D056804:Biofuels; D002247:Carbon Isotopes; D005579:Fossil Fuels; D001335:Vehicle Emissions; D000431:Ethanol