HR: 17:30h
AN: A14C-06    [Abstracts]
TI: Observational Constraints on the Global Budget of Ethanol
AU: * Naik, V
EM: vnaik@princeton.edu
AF: Woodrow Wilson School of Public and International Affairs, Princeton University, Robertson Hall, Princeton, NJ 08544, United States
AU: * Naik, V
EM: vnaik@princeton.edu
AF: Program in Atmospheric and Oceanic Sciences, Princeton University, Sayre Hall, 08544, NJ 08540, United States
AU: Fiore, A M
EM: Arlene.Fiore@noaa.gov
AF: NOAA/GFDL, 201 Forrestal Rd., Princeton, NJ 08542, United States
AU: Horowitz, L W
EM: Larry.Horowitz@noaa.gov
AF: NOAA/GFDL, 201 Forrestal Rd., Princeton, NJ 08542, United States
AU: Singh, H B
EM: Hanwant.B.Singh@nasa.gov
AF: NASA Ames Research Center, MS 245 5 21 Langley Blvd, Moffett Field, CA 94035, United States
AU: Wiedinmyer, C
EM: christin@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States
AU: Guenther, A B
EM: guenther@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States
AU: de Gouw, J
EM: Joost.deGouw@noaa.gov
AF: NOAA ESRL Chemical Sciences Division, 325 Broadway, Boulder, CO 80305,
AU: Millet, D
EM: millet@eps.harvard.edu
AF: Harvard University, Department of Earth and Planetary Sciences, 29 Oxford St, Cambridge, MA 02138,
AU: Levy, H
EM: Hiram.Levy@noaa.gov
AF: NOAA/GFDL, 201 Forrestal Rd., Princeton, NJ 08542, United States
AU: Oppenheimer, M
EM: omichael@princeton.edu
AF: Woodrow Wilson School of Public and International Affairs, Princeton University, Robertson Hall, Princeton, NJ 08544, United States
AU: Oppenheimer, M
EM: omichael@princeton.edu
AF: Program in Atmospheric and Oceanic Sciences, Princeton University, Sayre Hall, 08544, NJ 08540, United States
AB: Ethanol, an oxygenated volatile organic compound (OVOC), is used extensively as a motor fuel and fuel additive to promote clean combustion. Ethanol can affect the oxidizing capacity and the ozone-forming potential of the atmosphere. Limited available atmospheric observations suggest a global background atmospheric ethanol mixing ratio of about 20 pptv, with values up to 3 ppbv near source regions; however, the atmospheric distribution and budget of ethanol remain poorly understood. Here, we use the global three-dimensional chemical transport model MOZART-4 to investigate the global ethanol distribution and budget, and place constraints on the budget by evaluating the model with atmospheric observations. We implement a global ethanol source of 14.7 Tg yr-1 in the model consisting of biogenic emissions (9.2 Tg yr-1), industrial/anthropogenic emissions (3.2 Tg yr-1), emissions from biofuels (1.8 Tg yr-1), biomass burning emissions (0.5 Tg yr-1), and a secondary source from atmospheric production (0.056 Tg yr-1). Gas-phase oxidation by the hydroxyl radical accounts for 66% of the global sink of ethanol in the model, dry deposition 9%, and wet scavenging 25%. The simulation yields a global mean ethanol burden of 0.11 Tg and an atmospheric lifetime of 3 days. The simulated boundary layer mean ethanol concentrations underestimate observations from field campaigns over the United States by 50%, downwind of Asia by 76% and over the remote Pacific Ocean by 86%. Because of the short lifetime of ethanol, the model discrepancy over remote tropical regions cannot be attributed to an underestimate of surface emissions over continents. In these regions, the dominant model source is secondary atmospheric production, from the reaction of the ethyl peroxy radical (C2H5O2) either with itself or with the methyl peroxy radical (CH3O2). A ~500-fold increase in this diffuse source (to ~30 Tg yr-1) distributed uniformly throughout the troposphere would largely correct the observation-model mismatch, resulting in a best estimate of the global ethanol source of 44 Tg yr-1. This finding could indicate omission of other chemical species in the model that can provide additional sources of C2H5O2. Candidate OVOCs, such as propionaldehyde, and peroxypropionic nitric anhydride (PPN) that are precursors to C2H5O2, have been measured in the remote troposphere. This hypothesis, however, needs testing by direct measurements of C2H5O2 in the remote tropical troposphere.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0365 Troposphere: composition and chemistry
DE: 0368 Troposphere: constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting