Ozone cycling, nitric oxide

Effect of Nitric Oxide on Ozone Depletion. Nitrous oxide is injected into the atmosphere from natural sources on earth about 10% is converted to nitric oxide (N20 + 0( D) — 2 NO), which in turn can catalyze the destmction of ozone (11,32,75). The two main cycles are 1 and 2. Rate constant data are given in Reference 11. 

B. Nitric Oxide, Nitrogen Dioxide, and Ozone Cycles... 

The role of biomass in the natural carbon cycle is not well understood, and in the light of predictions of a future atmospheric energy balance crisis caused by carbon dioxide accumulation, in turn the result of an exponential increase in the consumption of carbon fuel, the apparent lack of concern by scientists and policy makers is most troubling. Yet there is no other single issue before us in energy supply which will require action long before the worst effects of excess production will be apparent. The only satisfactory model is the action taken by the R D community with respect to the SST in nitric oxide potential and chloro-halocarbon emissions, when it was realised that the stratospheric ozone layer was vulnerable to interference. Almost all other responses to pollution" have been after definitive effects have become apparent. 

Nitrous oxide is nontoxic—it used as the propellant in whipped-cream spray cans—and so might seem to be an unlikely pollutant. However, as noted earlier, it may contribute significantly to greenhouse warming. Furthermore, on diffusing to the stratosphere, N20 becomes involved in the ozone cycle (reactions 8.2, 8.3, and 8.6) following its conversion to nitric oxide (NO) ... 

Minor species observed in the stratosphere are shown in Fig. VIII-11. Of these it is now believed that nitric oxide is the most effective agent to destroy ozone by a catalytic cycle... 

FIGURE 4-35 The 03-N0x cycle. The cycle is driven by sunlight brown-colored nitrogen dioxide gas (N02) absorbs a photon and dissociates into nitric oxide (NO) and a highly reactive oxygen atom, which combines with an oxygen molecule to form ozone (03). The ozone can be reduced back to 02 by reaction with nitric oxide. The amount of 03 formed in this cycle cannot exceed the amount of N02 initially present in the air unless alternative means of regenerating N02 from NO exist such means can be provided by free radicals such as HOy or ROy. 

The largest variability in solar output is generally observed at the shortest wavelengths. Extreme ultraviolet radiation varies by a factor of two or more over an 11-year solar cycle, and produces nitric oxide in the thermosphere. As already mentioned, NO can be transported to the mesosphere and, to some extent, in winter even to the upper stratosphere where it can perturb upper stratospheric ozone. This is an indirect mechanism linking solar activity at short wavelengths (which do not penetrate below the lower thermosphere) to chemistry at lower altitudes. 

Nitric oxide (NO) plays a central role in atmospheric chemistry, influencing both ozone cycling and the tropospheric oxidation capacity through reactions with hydroperoxy- and organic peroxy-radicals. When the NO concentration exceeds 40 pptv (pptv = parts per trillion by volume) it catalyzes the production of ozone (O3) ... 

In the late 1960s, direct observations of substantial amounts (3ppb) of nitric acid vapor in the stratosphere were reported. Crutzen [118] reasoned that if HN03 vapor is present in the stratosphere, it could be broken down to a degree to the active oxides of nitrogen NO (NO and N02) and that these oxides could form a catalytic cycle (or the destruction of the ozone). Johnston and Whitten [119] first realized that if this were so, then supersonic aircraft flying in the stratosphere could wreak harm to the ozone balance in the stratosphere. Much of what appears in this section is drawn from an excellent review by Johnston and Whitten [119]. The most pertinent of the possible NO reactions in the atmosphere are... 

Society is facing several crucial issues involving atmospheric chemistry, Species containing nitrogen are major players in each. In the troposphere, nitrogen species are catalysts in the photochemical cycles that form ozone, a major urban and rural pollutant, as well as other oxidants (references 1 and 2, and references cited therein), and they are involved in acid precipitation, both as one of the two major acids (nitric acid) and as a base (ammonia) (3, 4). In the stratosphere, where ozone acts as a shield for the... 

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