Stratospheric chemistry nitrous oxide

Globally, the oxides of nitrogen, NO (nitric oxide), NO2 (nitrogen oxide), and N2O (nitrous oxide), are key species involved in the chemistry of the troposphere and stratosphere. NO and N2O are produced mostly by microbial soil activity, whereas biomass burning is also an important source of NO. Nitric oxide is a species involved in the photochemical production of ozone in the troposphere, is involved in the chemical produaion of nitric acid, and is an important component of acid precipitation. Nitrous oxide plays a key role in stratospheric ozone depletion and is an important greenhouse gas, with a global warming potential more than 200 times that of CO2. 

The speed at which things go in this business means that those of us who are on the fringes of it are always out of date, because by the time you have mastered the chemistry of 1979, you have replaced it widi the chemistry of 1983. So let me ask this question. There has been a great deal of emphasis here on CIO and on the role of chlorine in the ozone depletion but years ago from Paul Crutzen I learned the lesson that it was the nitrous oxide of the stratosphere and not Sherry Rowland s halocarbons that really held die control of the thing. Joking aside, the upfluxing molecules that do the damage — or do the necessary control, — what are they They are water vapor, they are methane, clearly they are synthetic halocarbons, but what is left of the statement that I had learned a few years ago that perhaps the major control is that due to N2O on its way up ... 

The process of dissimilatory dentrification occurs anaerobically and is mediated by bacteria that use nitrate in place of oxygen as an acceptor of electrons during respiration. The result is the formation of molecular nitrogen and nitrous oxide. The nitrous oxide plays a role in the chemistry of stratospheric ozone and is, therefore, extremely important bio-geochemically. These bacteria are heterotrophic and derive energy from the anaerobic oxidation of organic compounds. 

Other processes that could contribute to upper stratospheric ozone changes include trends in methane, nitrous oxide, and water vapor. These source gases can, for example, lead to changes in HOx and NOx, which can in turn affect ozone loss rates and the competition between different catalytic cycles. However, the effect of these changes is considerably smaller than the dramatic impact of the five-fold enhancement in chlorine caused by human activities. By the turn of the 21st century, observations and modelling studies showed that chlorine chemistry dominated the trends found in upper stratospheric ozone (see Muller et al., in WMO/UNEP, 1999). 

Discuss the role of nitrous oxides in stratospheric chemistry of ozone. Discuss the relative importance of this species in ozone destruction. 

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