Nitric oxide in the stratosphere

Reaction (13a) is the principal production process of nitric oxide in the stratosphere.5... 

Nitrous oxide (N2O) is a long-lived (120 yr) trace component of the atmosphere (Prinn et al., 1990). It is a climate-active gas as it has a radiative forcing 300 times that of CO2, although N2O presently contributes only 5% to the total greenhouse effect (Schimel, 1996). N2O also acts as a source of nitric oxide in the stratosphere and therefore participates in the catalytic removal of ozone (Crutzen, 1970). It is produced as a reaction intermediate in both microbial denitrification and nitrification processes and at greater rates under conditions of low O2 (Law and Owens, 1990) (see Chapter 6.11 by Emerson and Hedges for more details). 

Nicolet, M., and W. Peetermans, The production of nitric oxide in the stratosphere by oxidation of nitrous oxide. Ann Geophys 28, 751, 1972. 

Mayor, E., Velasco, A.M., Martin, I. Photodissociation of the 5(0,0) and 5(1,0) bands of nitric oxide in the stratosphere and the mesosphere a molecular-adapted quantum defect orbital calculation of photolysis rate constants. J. Geophys. Res. 112, D13304 (2007). doi 10.1029/ 2007JD008643... 

Although the nitric acid molecule is subject to various reactions and to photodissociation, nevertheless it remains, and it becomes the most important of the molecules containing NO (HN04, N205, NO3,. . . ) in the lower stratosphere. However, it cannot accumulate because it crosses the tropopause into the troposphere, where it rapidly disappears because of its solubility in water. Thus, if N20 is the source of the nitrogen oxides in the stratosphere, nitric acid is the sink that prevents their accumulation beyond certain limits. But it is now known that the sequence of reactions (20), (21), and (22) results in a lower concentration of stratospheric ozone than would be possible in a pure oxygen atmosphere. 

When I had my thoughts about the nitrogen oxides, I didn t publish them for about two years. There were no supportive measurements of nitrogen oxides in the stratosphere. Then in 1969-1970, some papers reported the presence of nitric acid in the stratosphere. I knew that wherever there is nitric acid, there must be also NO and NO2. At that point I dared to publish my paper. 

Nicolet, M., and S. Cieslik, The photodissociation of nitric oxide in the mesophere and stratosphere. Planet Space Sci 28, 105, 1980. 

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. 

Brasseur, G., and M. Nicolet, Chemospheric processes of nitric oxide in the mesosphere and stratosphere. Planet Space Sci 21, 939, 1973. 

Fig. 3-7. Vertical distribution of nitrogen oxides and nitric acid in the stratosphere. Left Nitric oxide in the sunlit atmosphere the fields enclose data obtained with the chemiluminescence technique (Horvath and Mason, 1978 Roy et at, 1980 Ridley and Schiff, 1981 Ridley and Hastie, 1981) horizontal lines represent measurements by infrared optical techniques (Drummond and Jarnot, 1978 Roscoe etal., 1981 Loewenstein etal., 1978a,b). Center Nitrogen dioxide as observed by optical measurement techniques, day (d) and night (n) points indicate data from Murcray et al. (1974), Goldman et al. (1978), Blatherwick et at (1980) horizontal bars are from Drummond and Jarnot (1978) and Roscoe et al. (1981). The N205 profile was obtained by Toon et al. (1986) at sunrise. Right Nitric acid observed by in situ filter sampling (open points) (Lazrus and Gandrud, 1974) and by infrared spectroscopy and mass spectroscopy (solid points) (Fontanella et at, 1975 Harries et al., 1976 Evans et al., 1978 Arnold et al., 1980 Murcray et al. as quoted by Hudson, 1982 Fischer et at, 1985). The envelope gives the error range.

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. 

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... 

Nitrous oxide (N2O) is an important greenhonse gas with a radiative forcing effect 310 times that of CO2 and a lifetime in the troposphere of approximately 120 years. Part of the N2O is converted to NO in the stratosphere, and so contributes to depletion of ozone. Nitric oxide (NO) is very reactive in the atmosphere and has a lifetime of only 1-10 days. It contribntes to acidification and to reactions leading to the formation of ozone in the troposphere, and so also to global warming. 

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 ... 

As discussed in Chapter 2.A.1, most of the primary emissions of NO, (= NO + N02) are in the form of nitric oxide, NO. The overall oxidation sequence is conversion of NO to N02, which is ultimately converted to HNOj and other oxidized forms such as PAN. Even in the case of PAN, the end product is ultimately HN03 since PAN can decompose back to N02 (see Chapter 6.1). While there has been speculation that there are processes that can convert HNO, back into reactive forms, which could be important in both the troposphere and stratosphere (e.g., see Chat-field, 1994 Hauglustaine et al., 1996 and Lary et al., 1997), none have been confirmed to date to occur in the atmosphere. 

The concentration of nitrous oxide (N2O) in the atmosphere is increasing. This is a concern, since N2O has been identified as a greenhouse gas and as a source of ozoneconsuming NO in the stratosphere. A significant source of N2O to the atmosphere is production of adipic acid (AA), which is used in the production of nylon. Adipic acid is formed from reaction of cyclohexanol with nitric acid (HNO3) according to the scheme in Fig. 13.13. 

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... 

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... 

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. 

Minschwaner, K., and D.E. Siskind, A new calculation of nitric oxide photolysis in the stratosphere, mesosphere, and lower thermosphere. J Geophys Res 98, 20,401, 1993. 

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