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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D15, 4442, doi:10.1029/2002JD002916, 2003

Interannual variability and trend of CH4 lifetime as a measure for OH changes in the 1979–1993 time period

Frank Dentener

Institute for Environment and Sustainability, Joint Research Centre, Ispra, Italy


Wouter Peters

Instituut voor Marien en Atmosferisch Onderzoek Utrecht, Utrecht University, Utrecht, Netherlands


Maarten Krol

Instituut voor Marien en Atmosferisch Onderzoek Utrecht, Utrecht University, Utrecht, Netherlands


Michiel van Weele

Department of Applied Physics, Eindhoven University of Technology, Eindhoven, Netherlands


Peter Bergamaschi

Institute for Environment and Sustainability, Joint Research Centre, Ispra, Italy


Jos Lelieveld

Max-Planck-Institute for Chemistry, Mainz, Germany


Abstract

The interannual variability and trend in the CH4 lifetime, as a measure for global mean OH concentration, have been analyzed systematically with three-dimensional (3-D) chemistry-transport model simulations. It is shown that the global mean OH concentration is highly variable from year to year due to changes in meteorology, changes in tropospheric UV radiation intensities, and changes in chemical concentrations owing to variable emissions of photochemical precursor gases (CH4-CO-NMVOC-NO x ). The meteorological variability is taken into account with the ECMWF-ERA15 1979–1993 reanalysis. Satellite observations provide the observed changes in the stratospheric ozone concentrations. Emission inventories are used to account for trends in anthropogenic emissions and their patterns. For the period 1979–1993, our simulations indicate a decrease of the calculated global tropospheric methane lifetime from 9.2 to 8.9 years, corresponding to a positive OH trend of 0.24 ± 0.06% yr−1. The modeled trend is mostly determined by changes in the tropical tropospheric water vapor content, while the changes in photolysis rates and in surface emissions of reactive trace gases compensate in their effect on the calculated OH trend over the analyzed time period.

Received 6 September 2002; accepted 1 May 2003; published 2 August 2003.

Index Terms: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0325 Atmospheric Composition and Structure: Evolution of the atmosphere; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry.

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Citation: Dentener, F., W. Peters, M. Krol, M. van Weele, P. Bergamaschi, and J. Lelieveld (2003), Interannual variability and trend of CH4 lifetime as a measure for OH changes in the 1979–1993 time period, J. Geophys. Res., 108(D15), 4442, doi:10.1029/2002JD002916.