Observational evidence for interhemispheric hydroxyl parity

  • 11 September 2014

New research titled: “Observational evidence for interhemispheric hydorxyl parity,” appeared in the Sept. 11 issue of Nature.  The research, which is about the abundance of the hydroxyl radical on hemispheric scales,  is partially funded by CPO’s AC-4 program. 

The hydroxyl radical (OH) is a key oxidant involved in the removal of air pollutants and greenhouse gases from the atmosphere. According to the authors, the Northern to Southern Hemispheric OH concentration ratio is imporant for the understanding of emission estimates of atmospheric species such as nitrogen oxides and methane. Unfortunately, the understanding of the Northern to Southern Hemispheric OH concentration ratio  remains poorly constrained with a range of estimates from 0.85-1.4.

In this Nature paper, the authors determine the Northern to Southern Hemispheric (NH/SH) OH concentration ratio with the help of methyl chloroform data (a proxy for OH concentrations) and an atmospheric transport model, which accurately describes interhemispheric transport and modeled emissions.

The authors found that for 2004-2011, the model predicted an annual-mean NH-SH gradient of methyl chloroform that is a tight linear function of the modelled NH/SH radio in annual-mean OH.  They 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 measurements networks and aircraft campaigns.

The paper's 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.

To view the full article in Nature, visit: www.nature.com/nature/journal/v513/n7517/full/nature13721.html




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