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Deriving global OH abundance and atmospheric lifetimes for long-lived gases: A search for the alternative reference gas for CH3CCl3.

Published

Author(s)

Qing Liang, Martyn P. Chipperfield, Eric L. Fleming, Luke Abraham, Peter Braesicke, James B. Burkholder, John S. Daniels, Sandip Dhomse, Steven C. Hardiman, Charles H. Jackman, Douglas E. Kinnison, Stephen A. Montzka, Olaf Morgenstern, Archie McCulloch, Paul A. Newman, Vladimir L. Orkin, Giovanni Pitari, Matthew Rigby, Eugene Rozanov, Fiona Tummon, Guus J. Velders, Daniele Visioni

Abstract

An accurate estimate of global hydroxyl radical (OH) abundance is important for projections of air quality, climate, and stratospheric ozone layer recovery. As atmospheric concentration of methyl chloroform (MCF), the commonly used reference gas for OH abundance, approaches zero, it is imperative to find new MCF-alternative gas(es) to infer atmospheric OH. The lack of global bottom-up emissions is the primary obstacle in choosing an OH proxy gas. However, global emissions can be inferred using the observed mean concentration differences between the Northern Hemisphere and Southern Hemisphere (gradient-based emissions). Using the combination of HFC-32, HFC-134a, HFC-152a, and HCFC-22 in a gradient-trend-based two-box model approach, it is possible to derive global OH abundance and atmospheric lifetimes of the long-lived trace gases that are primarily removed by OH in the troposphere. Since the lifetimes of these OH- removed trace gases are linearly correlated with each other, the use of multiple compounds greatly improves the accuracy of the derived OH and lifetime estimates. However, the gradient- trend-based approach requires research efforts in atmospheric observations and 3-D modeling of these compounds that improve the estimates of their inter-hemispheric gradient, global emissions and hemispheric partition, and north-south exchange timescale. Reducing the kinetic uncertainties of the k-OH reaction rates is also needed.
Citation
Journal of Geophysical Research

Keywords

OH partial lifetime, GHGs, HFC-32, HFC-134a, HFC-152a, HCFC-22, inter-hemispheric concentration difference
Created November 4, 2017, Updated October 1, 2019