ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-5361-2010 Observational constraints on the global atmospheric budget of ethanol Naik V. 1 2 10 Fiore A. M. 3 Horowitz L. W. 3 Singh H. B. 4 Wiedinmyer C. 5 Guenther A. 5 de Gouw J. A. 6 7 Millet D. B. 8 Goldan P. D. 6 7 Kuster W. C. 6 Goldstein A. 9 Woodrow Wilson School, Princeton University, NJ, USA Program in Atmospheric and Oceanic Sciences, Princeton University, NJ, USA Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, NJ, USA NASA AMES, Moffett Field, CA, USA NCAR, Boulder, CO, USA NOAA Earth System Research Laboratory, Boulder, CO, USA Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA Department of Soil, Water and Climate, University of Minnesota, St. Paul, MN, USA University of California at Berkeley, Department of Environmental Science, Policy and Management, CA, USA now at: High Performance Technologies Inc./Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, NJ, USA 17 06 2010 10 12 5361 5370 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/5361/2010/acp-10-5361-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/5361/2010/acp-10-5361-2010.pdf

Energy security and climate change concerns have led to the promotion of biomass-derived ethanol, an oxygenated volatile organic compound (OVOC), as a substitute for fossil fuels. Although ethanol is ubiquitous in the troposphere, our knowledge of its current atmospheric budget and distribution is limited. Here, for the first time we use a global chemical transport model in conjunction with atmospheric observations to place constraints on the ethanol budget, noting that additional measurements of ethanol (and its precursors) are still needed to enhance confidence in our estimated budget. Global sources of ethanol in the model include 5.0 Tg yr<sup>−1</sup> from industrial sources and biofuels, 9.2 Tg yr<sup>−1</sup> from terrestrial plants, ~0.5 Tg yr<sup>−1</sup> from biomass burning, and 0.05 Tg yr<sup>−1</sup> from atmospheric reactions of the ethyl peroxy radical (C<sub>2</sub>H<sub>5</sub>O<sub>2</sub>) with itself and with the methyl peroxy radical (CH<sub>3</sub>O<sub>2</sub>). The resulting atmospheric lifetime of ethanol in the model is 2.8 days. Gas-phase oxidation by the hydroxyl radical (OH) is the primary global sink of ethanol in the model (65%), followed by dry deposition (25%), and wet deposition (10%). Over continental areas, ethanol concentrations predominantly reflect direct anthropogenic and biogenic emission sources. Uncertainty in the biogenic ethanol emissions, estimated at a factor of three, may contribute to the 50% model underestimate of observations in the North American boundary layer. Current levels of ethanol measured in remote regions are an order of magnitude larger than those in the model, suggesting a major gap in understanding. Stronger constraints on the budget and distribution of ethanol and OVOCs are a critical step towards assessing the impacts of increasing the use of ethanol as a fuel.

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