HR: 10:20h
AN: A52A-01 INVITED    [Abstracts]
TI: Top-down estimates of tropospheric OH: past and future
AU: * Krol, M
EM: krol@phys.uu.nl
AF: SRON/IMAU, Princetonplein 5, Utrecht, 3584 CC, Netherlands
AB: Since the start of the ALE (Atmospheric Lifetime Experiment) program, measurements of methyl chloroform (1,1,1 trichloro ethane, or MCF) have been used to estimate tropospheric OH concentrations. These top-down estimates of OH are obtained by minimizing differences between measured and modeled MCF concentrations in an inverse modelling framework. Historic controversies about the inverse methodology will be reviewed. These controversies include the discussion on (i) whether or not initial MCF concentrations should be optimised (ii) how well emission estimates of MCF can be trusted, and (iii) the role of model errors. These details become important if, apart from a long-term average OH concentration, also information about the year-to-year variation of OH is obtained in the inverse procedure. Due to the Montreal protocol and its amendments, recent emissions of MCF have become very small. Hence, the atmospheric MCF concentrations strongly reflect the oxidizing action of OH. From the decaying burden of MCF in the atmosphere it should in the case of negligible emissions be possible to deduce year-to-year variations in OH. Recent progress in this field will be reviewed and alternatives for the vanishing OH-calibration gas MCF will be discussed.
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
DE: 1610 Atmosphere (0315, 0325)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting