1Woodrow Wilson School, Princeton University, NJ, USA
2Program in Atmospheric and Oceanic Sciences, Princeton University, NJ, USA
3Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, NJ, USA
4NASA AMES, Moffett Field, CA, USA
5NCAR, Boulder, CO, USA
6NOAA Earth System Research Laboratory, Boulder, CO, USA
7Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
8Department of Soil, Water and Climate, University of Minnesota, St. Paul, MN, USA
9University 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
Received: 20 Dec 2009 – Discussion started: 18 Jan 2010
Abstract. 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−1 from industrial sources and biofuels, 9.2 Tg yr−1 from terrestrial plants, ~0.5 Tg yr−1 from biomass burning, and 0.05 Tg yr−1 from atmospheric reactions of the ethyl peroxy radical (C2H5O2) with itself and with the methyl peroxy radical (CH3O2). 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.
Revised: 20 May 2010 – Accepted: 07 Jun 2010 – Published: 17 Jun 2010
Naik, V., Fiore, A. M., Horowitz, L. W., Singh, H. B., Wiedinmyer, C., Guenther, A., de Gouw, J. A., Millet, D. B., Goldan, P. D., Kuster, W. C., and Goldstein, A.: Observational constraints on the global atmospheric budget of ethanol, Atmos. Chem. Phys., 10, 5361-5370, doi:10.5194/acp-10-5361-2010, 2010.