Observational evidence for interhemispheric hydroxyl-radical parity

TitleObservational evidence for interhemispheric hydroxyl-radical parity
Publication TypeJournal Article
Year of Publication2014
AuthorsPatra P.K, Krol M.C, Montzka SA, Arnold T., Atlas E.L, Lintner B.R, Stephens B.B, Xiang B., Elkins JW, Fraser PJ, Ghosh A., Hintsa E.J, Hurst D.F, Ishijima K., Krummel PB, Miller B.R, Miyazaki K., Moore F.L, Mühle J, O'Doherty S, Prinn RG, Steele LP, Takigawa M., Wang H.J, Weiss RF, Wofsy S.C, Young D
Date Published2014/09
Type of ArticleArticle
ISBN Number0028-0836
Accession NumberWOS:000341362800047
Keywordsatmospheric hydroxyl; chemistry; climate; methane; methyl chloroform; model; sulfur-hexafluoride; transport; tropospheric oh; variability

The hydroxyl radical (OH) is a key oxidant involved in the removal of air pollutants and greenhouse gases from the atmosphere(1-3). The ratio of Northern Hemispheric to Southern Hemispheric (NH/SH) OH concentration is important for our understanding of emission estimates of atmospheric species such as nitrogen oxides and methane(4-6). It remains poorly constrained, however, with a range of estimates from 0.85 to 1.4 (refs 4,7-10). Here we determine the NH/SH ratio of OH with the help of methyl chloroform data (a proxy for OH concentrations) and an atmospheric transport model that accurately describes interhemispheric transport and modelled emissions. We find that for the years 2004-2011 the model predicts an annual mean NH-SH gradient of methyl chloroform that is a tight linear function of the modelled NH/SH ratio in annual mean OH. We estimate a NH/SH OH ratio of 0.97 +/- 0.12 during this time period by optimizing global total emissions and mean OH abundance to fit methyl chloroform data from two surface-measurement networks and aircraft campaigns(11-13). Our findings suggest that top-down emission estimates of reactive species such as nitrogen oxides in key emitting countries in the NH that are based on a NH/SH OH ratio larger than 1 may be overestimated.

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