HR: 10:50h
AN: A52A-03 INVITED    [Abstracts]
TI: Interannual Variability in Atmospheric Hydroxyl as Inferred From Measurements of CH₃CCl₃, CH₄, and Other Trace Gases
AU: * Montzka, S A
EM: Stephen.A.Montzka@noaa.gov
AF: NOAA/ESRL, 325 Broadway, Boulder, CO 80305, United States
AU: Dlugokencky, E
EM: Ed.Dlugokencky@noaa.gov
AF: NOAA/ESRL, 325 Broadway, Boulder, CO 80305, United States
AB: Interannual variations in the abundance of the atmospheric hydroxyl radical (OH) have been inferred from observations of certain long-lived trace gases. Accurate estimates of OH variability are possible provided emission magnitudes of a trace gas are precisely known or insignificant and provided variations in global mean trace gas mixing ratios are well characterized. Analyses conducted previously of CH₄ and CH₃CCl₃ observations prior to 1998 suggest very different conclusions regarding the stability of OH from year to year: while the CH₃CCl₃ data imply relatively large interannual OH changes (8%), CH₄ data suggest only a small interannual variability in OH (1-2%). Since 1998, however, we will show that the observations of both CH₄ and CH₃CCl₃ suggest relatively small interannual variations in the global atmospheric OH burden. Although the underlying causes for the discrepancy inferred for OH before 1998 are not well known, we argue here that the consistency inferred for OH variability in recent years is likely the result of an enhanced ability of CH₃CCl₃ measurements to discern OH variability since 1998, a period when CH₃CCl₃ emissions and atmospheric gradients were substantially diminished. Furthermore, during this latter period we have noted a similar phase to changes in the atmospheric growth rates of multiple trace gases including CH₄, CH₃CCl₃, CH₃Cl, and C₂Cl₄. While some of these similarities arise from variations in a common source ( e.g., biomass burning), for those not produced in substantial quantities from burning (CH₃CCl₃ and C₂Cl₄) a coherent picture regarding OH variability and phasing has emerged.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0322 Constituent sources and sinks
DE: 0365 Troposphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting