NEW INSIGHTS ON THE USE OF ETHANOL IN AUTOMOTIVE FUEL: A STABLE ISOTOPIC TRACER FOR FOSSIL FUEL COMBUSTION INPUTS TO THE ATMOSPHERE

 

Brian M. Giebel, Peter K. Swart, and Daniel D. Riemer

University of Miami – Rosenstiel School of Marine and Atmospheric Science

4600 Rickenbacker Causeway Miami, FL 33149

 

            Atmospheric ethanol has been receiving increased attention due to its use as a biofuel or fuel additive and because of the alcohol’s potential impact on air quality. We used stable isotopic ratio measurements of 13C/12C in ethanol emitted directly from vehicle exhaust and a small group of tropical plants to establish ethanol’s d13C source signatures. Ethanol emitted in the exhaust samples is distinctly different compared to that emitted from the 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 expected to be related to the alcohol’s origin from corn. 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 source 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.