Oxidizing power of the atmosphere

As we noted in Section 4.01.1, the ability of the troposphere to chemically transform and remove trace gases depends on complex chemistry driven by the relatively small flux of energetic solar UV radiation that penetrates through the stratospheric O3 layer (Levy, 1971 Chameides and Walker, 1973 Crutzen, 1979 Ehhalt et al., 1991 Logan et al, 1981 Ehhalt, 1999 Crutzen and Zimmerman, 1991). This chemistry is also driven by emissions of NO, CO, and hydrocarbons and leads to the production of O3, which is one of the important indicators of the oxidizing power of the atmosphere. But the most important oxidizer is the hydroxyl free radical (OH), and a key measure of the capacity of the atmosphere to oxidize trace gases injected into it is the local concentration of hydroxyl radicals. 

Since the presence (in very small quantities) of O D) in the troposphere results from the photolysis of ozone (see Reaction (5.16)), an assessment of the oxidizing power of the atmosphere requires that the global budget of tropospheric ozone be accurately quantified. 

The oxidizing power of the atmosphere has likely decreased significantly, especially in the Northern Hemisphere, as a result of human activities. As a result, the lifetime of methane may have increased by 10-15% since the preindustrial era. At the same time, the abundance of tropospheric ozone has increased perhaps by as much as a factor of 2-3 in the Northern Hemisphere. Enhanced biomass burning fluxes of NO CO, and hydrocarbons from tropical ecosystems are likely to be important. Future changes in tropospheric ozone are predicted to be largest in the tropics (India, China). These projected increases in tropical emissions are likely to have a... 

Since TO is a greenhouse gas, emissions of it can indirectly affect the formation of atmospheric greenhouse effect by influencing the TO concentration field. Moreover, MGC/TO precursors change the hydroxyl concentration field and, hence, the oxidation power of the troposphere. In its turn, the distribution of hydroxyl concentration in the troposphere controls the lifetime and, thus, the level of concentration of methane at the global scale. 

Hexavalent. Uranium hexafluoride, UFe, is one of the best-studied uranium compounds in existence due to its importance for uranium isotope separation and large-scale production ( 70 000 tons per year). All of the actinide hexafluorides are extremely corrosive white (U), orange (Np), or dark brown (Pu) crystalline solids, which sublime with ease at room temperature and atmospheric pressure. The synthetic routes into the hexafluorides are given in equation (13). The volatility of the hexafluorides increases in the order Pu < Np < U in the liquid state and Pu < U < Np in the solid state. UFe is soluble in H2O, CCI4, and other chlorinated hydrocarbons, is insoluble in CS2, and decomposes in alcohols and ethers. The oxidative power of the actinide hexafluorides are in line with the transition metal hexafluorides and the order of reactivity is as follows PuFg > NpFg > UFg > MoFe > WFe. The UFe molecule can also react with metal fluorides to form UF7 and UFg. The same reactivity is not observed for the Np and Pu analogs. 

Poisson, N. Kanakidou, M. Cmtzen, P.J., 2000 Impact of Non-methane Hydrocarbons on Tropospheric Chemistry and the Oxidizing Power of the Global Troposphere 3-Dimensional Modelling Results , in Journal of Atmospheric Chemistry, 36 157-230. 

Excess fertilizer and combustion processes also can increase nitrous oxide (NnO) and nitrogen oxides (NOx) in the atmosphere. Nitrous oxide is a powerful greenhouse gas, and nitrogen oxides lead to smog and acid rain. The production of fertilizers requires a great deal of energy. The use of fossil fuels to supply the thermal requirements for fertilizer production further increases emission of nitrogen compounds to the atmosphere. 

Apart from these intrinsic properties, extrinsic effects can be produced in many oxides by variation of the metal/oxygen ratio through control of the atmospheric oxygen potential. The p-type contribution is increased as the oxygen pressure increases, and the n-type contribution as the oxygen pressure decreases. The pressure dependence of these contributions can usually be described by a simple power dependence thus... 

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