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Deriving Global OH Abundance and Atmospheric Lifetimes for Long‐Lived Gases: A Search for CH 3 CCl 3 Alternatives
Author(s) -
Liang Qing,
Chipperfield Martyn P.,
Fleming Eric L.,
Abraham N. Luke,
Braesicke Peter,
Burkholder James B.,
Daniel John S.,
Dhomse Sandip,
Fraser Paul J.,
Hardiman Steven C.,
Jackman Charles H.,
Kinnison Douglas E.,
Krummel Paul B.,
Montzka Stephen A.,
Morgenstern Olaf,
McCulloch Archie,
Mühle Jens,
Newman Paul A.,
Orkin Vladimir L.,
Pitari Giovanni,
Prinn Ronald G.,
Rigby Matthew,
Rozanov Eugene,
Stenke Andrea,
Tummon Fiona,
Velders Guus J. M.,
Visioni Daniele,
Weiss Ray F.
Publication year - 2017
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2017jd026926
Subject(s) - trace gas , abundance (ecology) , southern hemisphere , atmospheric chemistry , ozone , freon , chemistry , atmospheric sciences , environmental science , northern hemisphere , climatology , environmental chemistry , physics , ecology , geology , biology , organic chemistry
An accurate estimate of global hydroxyl radical (OH) abundance is important for projections of air quality, climate, and stratospheric ozone recovery. As the atmospheric mixing ratios of methyl chloroform (CH 3 CCl 3 ) (MCF), the commonly used OH reference gas, approaches zero, it is important to find alternative approaches to infer atmospheric OH abundance and variability. The lack of global bottom‐up emission inventories is the primary obstacle in choosing a MCF alternative. We illustrate that global emissions of long‐lived trace gases can be inferred from their observed mixing ratio differences between the Northern Hemisphere (NH) and Southern Hemisphere (SH), given realistic estimates of their NH‐SH exchange time, the emission partitioning between the two hemispheres, and the NH versus SH OH abundance ratio. Using the observed long‐term trend and emissions derived from the measured hemispheric gradient, the combination of HFC‐32 (CH 2 F 2 ), HFC‐134a (CH 2 FCF 3 , HFC‐152a (CH 3 CHF 2 ), and HCFC‐22 (CHClF 2 ), instead of a single gas, will be useful as a MCF alternative to infer global and hemispheric OH abundance and trace gas lifetimes. The primary assumption on which this multispecies approach relies is that the OH lifetimes can be estimated by scaling the thermal reaction rates of a reference gas at 272 K on global and hemispheric scales. Thus, the derived hemispheric and global OH estimates are forced to reconcile the observed trends and gradient for all four compounds simultaneously. However, currently, observations of these gases from the surface networks do not provide more accurate OH abundance estimate than that from MCF.