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, 7-10). 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.
authors.affiliation: 1] Department of Environmental Geochemical Cycle Research, JAMSTEC, Yokohama 236 0001, Japan [2] CAOS, Graduate School of Studies, Tohoku University, Sendai 980 8578, Japan.
authors.forename: P K
authors.initials: PK
authors.lastname: Patra
authors.affiliation: Wageningen University, Droevendaalsesteeg 3a, 6708 PB, The Netherlands.
authors.forename: M C
authors.initials: MC
authors.lastname: Krol
authors.affiliation: National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory, Boulder, Colorado 80305, USA.
authors.forename: S A
authors.initials: SA
authors.lastname: Montzka
authors.affiliation: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: T
authors.initials: T
authors.lastname: Arnold
authors.affiliation: The Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida 33149, USA.
authors.forename: E L
authors.initials: EL
authors.lastname: Atlas
authors.affiliation: Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901, USA.
authors.forename: B R
authors.initials: BR
authors.lastname: Lintner
authors.affiliation: National Center for Atmospheric Research (NCAR), Boulder, Colorado 80301, USA.
authors.forename: B B
authors.initials: BB
authors.lastname: Stephens
authors.affiliation: School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: B
authors.initials: B
authors.lastname: Xiang
authors.affiliation: National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory, Boulder, Colorado 80305, USA.
authors.forename: J W
authors.initials: JW
authors.lastname: Elkins
authors.affiliation: Centre for Australian Weather and Climate Research, Commonwealth Scientific and Industrial Research Organisation (CSIRO) Oceans and Atmosphere Flagship, Aspendale, Victoria 3195, Australia.
authors.forename: P J
authors.initials: PJ
authors.lastname: Fraser
authors.affiliation: 1] Department of Environmental Geochemical Cycle Research, JAMSTEC, Yokohama 236 0001, Japan [2] National Institute of Polar Research, 10-3, Midoricho, Tachikawa, Tokyo 190-8518, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Ghosh
authors.affiliation: 1] National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory, Boulder, Colorado 80305, USA [2] CIRES, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Hintsa
authors.affiliation: 1] National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory, Boulder, Colorado 80305, USA [2] CIRES, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: D F
authors.initials: DF
authors.lastname: Hurst
authors.affiliation: Department of Environmental Geochemical Cycle Research, JAMSTEC, Yokohama 236 0001, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Ishijima
authors.affiliation: Centre for Australian Weather and Climate Research, Commonwealth Scientific and Industrial Research Organisation (CSIRO) Oceans and Atmosphere Flagship, Aspendale, Victoria 3195, Australia.
authors.forename: P B
authors.initials: PB
authors.lastname: Krummel
authors.affiliation: 1] National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory, Boulder, Colorado 80305, USA [2] CIRES, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: B R
authors.initials: BR
authors.lastname: Miller
authors.affiliation: Department of Environmental Geochemical Cycle Research, JAMSTEC, Yokohama 236 0001, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Miyazaki
authors.affiliation: 1] National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory, Boulder, Colorado 80305, USA [2] CIRES, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: F L
authors.initials: FL
authors.lastname: Moore
authors.affiliation: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: J
authors.initials: J
authors.lastname: Mühle
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, BS8 1TS, UK.
authors.forename: S
authors.initials: S
authors.lastname: O'Doherty
authors.affiliation: Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: R G
authors.initials: RG
authors.lastname: Prinn
authors.affiliation: Centre for Australian Weather and Climate Research, Commonwealth Scientific and Industrial Research Organisation (CSIRO) Oceans and Atmosphere Flagship, Aspendale, Victoria 3195, Australia.
authors.forename: L P
authors.initials: LP
authors.lastname: Steele
authors.affiliation: Department of Environmental Geochemical Cycle Research, JAMSTEC, Yokohama 236 0001, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Takigawa
authors.affiliation: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
authors.forename: H J
authors.initials: HJ
authors.lastname: Wang
authors.affiliation: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: R F
authors.initials: RF
authors.lastname: Weiss
authors.affiliation: School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: S C
authors.initials: SC
authors.lastname: Wofsy
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, BS8 1TS, UK.
authors.forename: D
authors.initials: D
authors.lastname: Young
mesh_terms: D000393:Air Pollutants / Q000737:chemistry; D001272:Atmosphere / Q000737:chemistry*; D002725:Chloroform / Q000737:chemistry; D003198:Computer Simulation; D017665:Hydroxyl Radical / Q000737:chemistry*; D008962:Models, Theoretical; D009589:Nitrogen Oxides / Q000737:chemistry
chemical_list: D000393:Air Pollutants; D009589:Nitrogen Oxides; D017665:Hydroxyl Radical; D002725:Chloroform