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Book ChapterDOI

5. Stratospheric Ozone: An Introduction to Its Study

03 Mar 2014-

AboutThe article was published on 2014-03-03 and is currently open access. It has received None citation(s) till now. The article focuses on the topic(s): Ozone layer.

Topics: Ozone layer (64%)

Summary (3 min read)

REACTIONS IN A HYDROGEN-OXYGEN ATMOSPHèRE

  • When an analysis of the various reaction rates is made, a certain number of them can be ignored, and for several years it was assumed [e.g.. Fig. 2 . Observed and calculated ozone profiles.
  • Hunt. 1966; Leovy. 1969] that the reactions of OH and HO2 radicals with O and Oj were the essential reactions explaining the aeronomic behavior of stratospheric ozone.
  • The normal photodissociation process (a,3) H2O + hv neS) + OH{Xm) (30) which can still occur in the stratosphère, is less important than the reaction process (29).
  • This reaction may be introduced into the aeronomic chemistry of molecular hydrogen.
  • The rate coefficient «20 should be of the same order of magnitude as 13,5, but no acceptable value has been found.

REACTIONS AFTER OXIDATION OF MéTHANE

  • Methyl radicals, which are produced by oxidation processes of CH,, may react rapidly with atomic oxygen (c) CH, + O -H + HjCO + 67 Iccal (63û) with u rate coefficient [Slagle et al..
  • According to Levy [1972] , CH,0,H either reacts with OH or is subject to photodissociation (c") CH,0,H + hv ^ CH,0 + OH (78) Finally, if methylperoxynitrite and methylperoxynitrate are formed, the photodissociation should be considered to be and (Oo) EQUATION Reactions of CH,, CH3O, and CHjO, with ozone have also been considered [Simonaitis and Heicklen, 1975a] .

ATMOSPHèRE

  • The présence of nitrogen oxides in the upper atmosphère requires the production of atomic nitrogen [Nicolei.
  • From this analysis of the various reactions of nitrogen trioxide, it is not clear if NO, can play a major rôle in stratospheric aeronomy.
  • Among the various dissociation processes, the authors may consider the following: Cl, + hv{\ < 483 nm) -2CI (159a) is photodissociated in the stratosphère and troposphère by radiation of X > 300 nm [Seery and Britton.

and

  • Thus the addition of nitrogen oxides NO and NO,, which destroy odd oxygen by various reactions involving ozone and atomic oxygen, must be considered with its counterpart, the photodissociation of NO, NO,, and NO, and the N formation, as production processes in addition to the photodissociation of molecular oxygen.
  • Furthermore, the differential équation for nitric oxide must be written as foilows:.
  • Thus the nitrogen oxide concentrations, and particularly those of HNOs, NO, and NO2, must dépend on atmospheric conditions in the lower stratosphère [Brasseur and Nicolet, 1973] , and their behavior will be related to the variation of the tropopause.

SOLAR RADIATION

  • The authors knowledge of solar radiation in the ultraviolet which plays a rôle in the photodissociation of molecular oxygen is due to rocket and balloon data.
  • The percentages are given for the spectral range AK = 500 cm"'; standard conditions prevail.
  • There is therefore no doubt that the stratospheric ozone below its concentration peak is essentially due to a downward transport from the production régions Figure 20 is another illustration of this distribution of the ozone formation resulting from the atomic oxygen production with a peak in the upper stratosphère between 40 and 50 km even for overhead sun conditions.
  • The température-altitude profiles indicate that the important différences occur between 10 and 20 km; they are related to the hcight of the tropopause and have therefore an effect on the rate coefficients in the lower stratosphère.

PHOTODISSOCIATION IN THE TROPOSPHèRE AND STRATOSPHèRE AND ITS EFFECTS

  • The photodissociation in the lower régions of the terrestrial atmosphère is of particular interest, since it is the necessary process to start various chemical reactions.
  • The ozone photolysis (see for example, Welge [1974] for a récent analysis of the photolysis of O», Hd, COj, and SO, compounds) occurs in the visible région in the spectral range of the Chappuis bands with production of oxygen molécules and atoms in their normal States.
  • Its concentration dépends on the exchange processes between the stratosphère and troposphère.
  • The absorption cross section of nitrous oxide varies within very low values less than 10"" cm^ between 310 and 250 nm, and its photodissociation coefficient is not greater than 10"' s"' at the stratopause and reaches only values less than 10"' S"' in the low stratosphère.
  • The photodissociation rates are relatively small, and departures from photochemical equilibrium conditions are aiways the rule.

FINAL INTRODUCTORY REMARKS

  • The authors have seen that it is aiways possible to résolve the theoretical problem of stratospheric ozone with the introduc-PHOTOOI SSOCIAT ION COEFFICIENT I sec"'l Fig. 37 . 1972] . tion of correct aeronomic équations and with the adoption oi the principal atmospheric parameters.
  • The boundary conditions, which are used in stratospheric models, are not aiways adopted to varying atmospheric conditions.
  • Seiler, 1974; Seiler and Schmidi, 1974] il may be pointed out that the CO concentration must be known with précision in the lower stratosphère in order to détermine the ratio n(OH)/«(H02).
  • In the same way, the tropospheric ozone problem requires more attention, since a photochemical theory has been proposed by Chameides and Walker [1973.

CONCENTRATION Icm"'')

  • Récent measurements by Schmidt [1974] and Seller and Schmidt [1974] lead to an almost constant mixing ratio ofO.55 ppm for tropospheric molecular hydrogen which can be taken as the normal mixing ratio above the tropopause level.
  • Sampling [Ehhall, 1974] in the stratosphère at various latitudes is required in order to obtain enough vertical profiles to compare with the calculated vertical distributions of méthane and molecular hydrogen.
  • It is not yet clear how the vertical and horizontal transports play their rôle [Wofsy et ai. 1967] , and even spécial sources [Deuser et al., 1973] .
  • Récent measurements at ground level of HNO2 by Nash [1974] lead to mixing ratios from 1 to 10 ppb which must be explained by its various reactions with nitrogen oxides and hydroxyl and hydroperoxyl radicals.

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01 Jun 1974-Nature
Abstract: Chlorofluoromethanes are being added to the environment in steadily increasing amounts. These compounds are chemically inert and may remain in the atmosphere for 40–150 years, and concentrations can be expected to reach 10 to 30 times present levels. Photodissociation of the Chlorofluoromethanes in the stratosphere produces significant amounts of chlorine atoms, and leads to the destruction of atmospheric ozone.

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Abstract: The probable importance of NO and NO2 in controlling the ozone concentrations and production rates in the stratosphere is pointed out. Observations on and determinations of nitric acid concentrations in the stratosphere by Murcray et al. (1968) and Rhine et al. (1969) support the high NO and NO2 concentrations indicated by Bates/Hays (1967). Some processes which may lead to production of nitric acid are discussed. The importance of O (1S), possibly produced in the ozone photolysis below 2340 A, on the ozone photochemistry is mentioned.

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09 Jul 1971-Science
TL;DR: A radical chain reaction is proposed for the rapid removal of carbon monoxide, leading to acarbon monoxide lifetime as low as 0.2 year in the surface atmosphere.
Abstract: A steady-state model of the normal (unpolluted) surface atmosphere predicts a daytime concentration of hydroxyl, hydroperoxyl, and methylperoxyl radicals approaching 5 x 10(8)molecules per cubic centimeter and a formaldehyde concentration of 5 x 10(10) molecules per cubic centimeter or 2 parts per billion. A radical chain reaction is proposed for the rapid removal of carbon monoxide, leading to a carbon monoxide lifetime as low as 0.2 year in the surface atmosphere.

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06 Aug 1971-Science
TL;DR: The projected increase in stratospheric oxides of nitrogen could reduce the ozone shield by about a factor of 2, thus permitting the harsh radiation below 300 nanometers to permeate the lower atmosphere.
Abstract: Although a great deal of attention has been given to the role of water vapor from supersonic transport (SST) exhaust in the stratosphere, oxides of nitrogen from SST exhaust pose a much greater threat to the ozone shield than does an increase in water. The projected increase in stratospheric oxides of nitrogen could reduce the ozone shield by about a factor of 2, thus permitting the harsh radiation below 300 nanometers to permeate the lower atmosphere.

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Abstract: Solar radiation dissociates water vapor into hydrogen atoms and hydroxyl radicles Hydrogen and hydrogen peroxide molecules, and perhydroxyl radicles, are also produced as a result of subsequent chemical reactions with the allotropic forms of oxygen The rate of the oxidizing processes falls off more rapidly with increase of altitude than does that of the reducing processes, and the hydrogen compounds are almost completely broken down at about the 90-km level (or even lower) There is a continual escape of the hydrogen atoms into interplanetary space; but the liberated oxygen atoms remain in the atmosphere, and the number that must thus have been added in geological time seems to be comparable with the number now present Consideration of the general equilibrium reveals several features of interest, such as, for example, the existence of a thin layer of molecular hydrogen In spite of the prominence of the Meinel bands, the concentration of hydroxyl radicles is quite small It is thought that these radicles are excited during, rather than after, their formation The mechanism proposed is two body collisions between hydrogen atoms and ozone molecules

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