Nitric oxide ozone destruction

In order to calculate the steady-state concentration of ozone in the stratosphere, we need to balance the rate of production of odd oxygen with its rate of destruction. Chapman originally thought that the destruction was due to the reaction O + 03 —> 2O2, but we now know that this pathway is a minor sink compared to the catalytic destruction of 03 by the trace species OH, NO, and Cl. The former two of these are natural constituents of the atmosphere, formed primarily in the photodissociation of water or nitric oxide, respectively. The Cl atoms are produced as the result of manmade chlorofluorocarbons, which are photodissociated by sunlight in the stratosphere to produce free chlorine atoms. It was Rowland and Molina who proposed in 1974 that the reactions Cl + 03 —> CIO + O2 followed by CIO + O —> Cl + O2 could act to reduce the concentration of stratospheric ozone.10 The net result of ah of these catalytic reactions is 2O3 — 3O2. 

The actual destruction of ozone in the stratosphere actually involves hundreds of different reactions. Besides the Chapman reactions and destruction by CFCs, many other chemical species can destroy ozone. In 1970, Paul Crutzen (193 3-) showed that nitrogen oxides could destroy ozone. Nitric oxide can remove an oxygen atom from ozone and be regenerated according to the following reactions ... 

PROBLEM 13.23 Nitric oxide emitted from the engines of supersonic transport planes can contribute to the destruction of stratospheric ozone ... 

Nitric oxide emissions from supersonic aircraft can contribute to destruction of the ozone layer. 

Nitric oxide, NO-, is another radical also thought to cause ozone destruction by a similar mechanism. One source of NO- in the stratosphere is supersonic aircraft whose jet engines convert small amounts of Ng and Og to NO-. Write the propagation steps for the reaction of Og with NO. 

Ozone, in turn, can be destroyed by interaction with another photon that breaks it into an oxygen molecule (02) and an oxygen atom (O). Stratospheric ozone also can be destroyed by reaction with other species, such as nitric oxide (NO) — as in Eq. [4-35], and chlorine atoms (from CFCs). The net concentration of ozone is established by the rates of both the production and destruction reactions. 

Another group of compounds that can destroy stratospheric ozone are the nitrogen oxides, generally denoted as NO. (Examples of NO are NO, NO2, N2O, and N2O5.) These compounds come from the exhausts of high-altitude supersonic aircraft and from human and natural activities on Earth. Solar radiation decomposes a substantial amount of the other nitrogen oxides to nitric oxide (NO), which participates in the destruction of ozone as follows ... 

The catalytic destruction of ozone by NO is the most important process that occurs in the middle and upper stratosphere. We should stress here that this process is possible even in unpolluted atmosphere since small amounts of nitrous oxide, N2O, from biological denitrification have always been present in the stratosphere, which is the precursor of nitric oxide, NO, in reaction with atomic oxygen (reaction (11)). Most collisions with atomic oxygen form N2 and O2, but a few form NO (see also Section 4)... 

Nitric oxide is formed in the combustion of fossil fuels and is present in automobile and power plant exhausts it can also be formed from the action of lightning on atmospheric N2 and O2. In the atmosphere, NO is oxidized to NO2. These gases, often collectively des-—E 2 HNO3 -E NO ignated NO., contribute to acid rain, primarily because NO2 reacts with atmospheric water to form nitric acid. Nitrogen oxides are also believed to be instrumental in the destruction of the Earth s ozone layer (Section 8.8.1). 

Reaction sequence for ozone destruction promoted by nitric oxide. 

Hydroxyl radicals (OH) and nitric oxide (NO) radicals can promote the destruction of ozone. 

The research of Paul Crutzen, the third recipient of the Nobel Prize for Chemistry in 1995, involved the effect of nitric oxide (NO) on the destruction of stratospheric ozone. Unlike CFCs, which may take 50 to 100 years to diffuse into the upper atmosphere, nitric oxide is introduced directly to the stratosphere in the exhaust of high-altitude aircraft. Early in the 1970s, the United States considered construction of a large fleet of supersonic transport airplanes (SSTs), similar to the Concorde. Environmentalists argued, based in part on the work of Paul Crutzen, that to do so would significantly endanger the ozone layer. 

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... 

Coupled closely with the effect causing horizontal distributions are the vertical distributions of ozone concentrations. These distributions have an intimate influence on the urban-rural interchange of ozone. Miller and Ahrens presented detailed vertical time and space cross sections of ozone concentrations at altitudes up to 2,500 m. A low-altitude temperature inversion may actually lead to lower concentrations of oxidant, because the destruction rate can be increased by the injection of nitric... 

The importance of catalysts in chemical reactions cannot be overestimated. In the destruction of ozone previously mentioned, chlorine serves as a catalyst. Because of its detrimental effect to the environment, CFCs and other chlorine compounds have been banned internationally. Nearly every industrial chemical process is associated with numerous catalysts. These catalysts make the reactions commercially feasible, and chemists are continually searching for new catalysts. Some examples of important catalysts include iron, potassium oxide, and aluminum oxide in the Haber process to manufacture ammonia platinum and rhodium in the Ostwald synthesis of nitric... 

The last step in the current manufacture of adipic acid involves oxidation by nitric acid, which results in the formation of nitrous oxide (N2O) that is released into the atmosphere. Given that N2O has no tropospheric sinks, it can rise to the stratosphere and be a factor in the destruction of the ozone layer. It also acts as a greenhouse gas (see Section 8.4.1). 

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