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5. Stratospheric Ozone: An Introduction to Its Study

About: The article was published on 2014-03-03 and is currently open access. It has received None citations till now. The article focuses on the topics: Ozone layer.

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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Journal ArticleDOI
TL;DR: In this article, an autocatalytic chain removal of both reactants was found to be at least partially due to an auto-catalysis chain removal in discharge-flow systems, and diagnostic tests suggested that OH, NO2, and NO3 are the chain carriers.
Abstract: The reactions have been studied in a discharge-flow system. Kinetic studies were made using resonance fluorescence for the measurement of atom concentrations. Based on the rates of atom loss, the following upper limits were obtained for the rate constants: Observed reaction in the HHNO3 system is at least partially due to an autocatalytic chain removal of both reactants. Diagnostic tests have suggested that OH, NO2, and NO3 are the chain carriers.

13 citations

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TL;DR: The solar ultraviolet flux in the wavelength bands 1580-1640 A and 1430-1470 A (FWHM) was measured using photon ion chambers carried on the satellite WRESAT I (1967-118A) as mentioned in this paper.
Abstract: The solar ultraviolet flux in the wavelength bands 1580–1640 A and 1430–1470 A (FWHM) has been measured using photon ion chambers carried on the satellite WRESAT I (1967-118A). These observations of the integrated ultraviolet flux from the entire disk indicate a value of (4570 ± 50) K for the solar temperature minimum. The results are compared with other estimates of the minimum value of the solar brightness temperature.

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Journal ArticleDOI
TL;DR: In this paper, the absolute intensities and the centre-to-limb variations of the Sun at three wavelengths of 1629 A, 1684 A, and 1739 A were measured by a rocket-borne spectrometer flown from the Kagoshima Space Centre on 1 September 1971.
Abstract: The absolute intensities and the centre-to-limb variations of the Sun at three wavelengths of 1629 A, 1684 A, and 1739 A were measured by a rocket-borne spectrometer flown from the Kagoshima Space Centre on 1 September 1971. The spectrometer was a double-dispersive trichrometer, whose spectral and spatial resolutions were 8.3 A and 1.3 respectively. The results concerning the absolute intensities were similar to those measured by the Harvard College Observatory group. The results for the centre-to-limb variation at 1629 A and 1684 A seem to support the HSRA model but not those at 1739 A.

11 citations

Journal ArticleDOI
TL;DR: In this article, the authors have described and given the results of a theoretical calculation of the distribution of atmospheric ozone, considering the ozone to be maintained in a photochemical steady state by solar radiation that is absorbed by oxygen and ozone.
Abstract: In the last issue of this Journal the authors have described and given the results of a theoretical calculation of the distribution of atmospheric ozone1, considering the ozone to be maintained in a photochemical steady state by solar radiation that is absorbed by oxygen and ozone. The resulting distribution resembles rather closely the actual distribution so far as it is now known from observation, and suggests that the photochemical picture is adequate to account for the major aspects of atmospheric ozone. Certain factors not taken into account in the calculation, but which are of importance for the complete picture, were briefly discussed at the end of the above-mentioned paper. Two of these were the influence of the absorption of ozone in the visible spectrum (the Chappuis bands) and the influence of air-movements on the amount of ozone over any particular point on the Earth's surface. It is the purpose of this and another short article, which will follow to expand upon these two points.

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