HR: 1330h
AN: A52B-0791    [PDF]
TI: An Upward Revision of Current Estimates for the Atmospheric Lifetimes of Methane and Other Pollutants Removed by OH
AU: * Wang, J S
EM: james.wang@stanfordalumni.org
AF: Environmental Defense, 257 Park Avenue South, 17th Floor, New York, NY 10010 United States
AU: * Wang, J S
EM: james.wang@stanfordalumni.org
AF: Harvard University, Dept. of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, 29 Oxford Street, Cambridge, MA 02138 United States
AU: McElroy, M B
EM: mbm@io.harvard.edu
AF: Harvard University, Dept. of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, 29 Oxford Street, Cambridge, MA 02138 United States
AU: Logan, J A
EM: jal@io.harvard.edu
AF: Harvard University, Dept. of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, 29 Oxford Street, Cambridge, MA 02138 United States
AB: An inverse modeling study using observations of methyl chloroform (MCF) and the 3-D GEOS-CHEM chemical transport model with assimilated meteorology was conducted to estimate the global abundance of hydroxyl radical (OH). Our method differs from those of previous inversion studies in that we optimized both the emissions of MCF and the abundance of OH, we used winds specific to the analysis years, and we ran the model at a finer spatial resolution. Inversions were carried out for the years 1987-1993. High-frequency observations from the GAGE/AGAGE and CMDL networks were used in separate analyses. We inverted for MCF emissions from each of a number of regions. Different variations of the inversion optimizing global or hemispheric abundances of OH were implemented. We find that global emissions of MCF are about 10% lower than previous estimates for earlier years in the analysis period, before emissions declined precipitously in response to the phase-out of MCF production; our emissions estimates are more similar to previous estimates for later years. This result appears to be consistent with observations of MCF pollution plumes in the late 1990s, which suggest that the time lag between purchases and emissions of MCF may be longer than previously thought. Our estimate for the lifetime of MCF with respect to OH, 7.0-7.7 years, is 17%-35% longer than those of previous studies. The corresponding lifetime for methane is about 12 years, as compared to the 10.1 years estimated by a previous study. Photochemical calculations using recent versions of the GEOS-CHEM model also suggest a lower abundance of OH. Our results have important implications for the global warming potentials (GWPs) of methane and other greenhouse gases removed primarily by OH.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0317 Chemical kinetic and photochemical properties
DE: 0322 Constituent sources and sinks
DE: 0365 Troposphere--composition and chemistry
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting