@article{48cb9173fa1741fea43f7333af0c35d8,
title = "Observational evidence for interhemispheric hydroxyl-radical parity",
abstract = "The hydroxyl radical (OH) is a key oxidant involved in the removal of air pollutants and greenhouse gases from the atmosphere. 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. It remains poorly constrained, however, with a range of estimates from 0.85 to 1.4 (refs 4, 7,8,9,10). 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. 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.",
author = "Patra, {P. K.} and Krol, {M. C.} and Montzka, {S. A.} and T. Arnold and Atlas, {E. L.} and Lintner, {B. R.} and Stephens, {B. B.} and B. Xiang and Elkins, {J. W.} and Fraser, {P. J.} and A. Ghosh and Hintsa, {E. J.} and Hurst, {D. F.} and K. Ishijima and Krummel, {P. B.} and Miller, {B. R.} and K. Miyazaki and Moore, {F. L.} and J. M{\"u}hle and S. O'Doherty and Prinn, {R. G.} and Steele, {L. P.} and M. Takigawa and Wang, {H. J.} and Weiss, {R. F.} and Wofsy, {S. C.} and D. Young",
note = "Funding Information: Acknowledgements We thank the HIPPO science team and the crew and support staff at the NCAR Research Aviation Facility, and all the laboratory staff working for AGAGE and NOAA measurement networks. This work is partly supported by the Japan Society for the Promotion of Science/Grants-in-Aid for Scientific Research (KAKENHI) Kiban-A (grant no. 22241008) and Ministry of Education, Culture, Sports, Science and Technology (MEXT) Arctic GRENE projects. NCAR is sponsored by the National Science Foundation (NSF). HIPPO was supported by NSF grants ATM-0628575, ATM-0628519, ATM-0628388 ATM-0628452 and ATM-1036399, by NASA award NNX11AF36G, and by NCAR. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of NSF, NOAA or NASA. M.C.K. is supported by EU FP7 project PEGASOS. AGAGE is supported principally by NASA grants to Massachusetts Institute of Technology (NNX11AF17G) and Scripps Institution of Oceanography (NNX11AF16G) and also by NOAA and the CSIRO. Mace Head is supported by the Department of Energy and Climate Change, award GA0201. We thank the CSIRO OceansandAtmosphere FlagshipandtheBureauofMeteorologyfor CapeGrimproject funding. NOAA flask measurements are supported in part by NOAA{\textquoteright}s Climate Program Office and its Atmospheric, Chemistry, Carbon Cycle and Climate Program. Publisher Copyright: {\textcopyright}2014 Macmillan Publishers Limited. All rights reserved.",
year = "2014",
month = sep,
day = "11",
doi = "10.1038/nature13721",
language = "English (US)",
volume = "513",
pages = "219--223",
journal = "Nature",
issn = "0028-0836",
publisher = "Nature Publishing Group",
number = "7517",
}