Ozone absorption cross-section

Table 4.3 shows the ozone absorption cross sections (base e) at 298 and at 226 K measured by Molina and Molina (1986), with which recent studies are in agreement, particularly below 240 nm (e.g., see Malicet et al., 1995 DeMore et al., 1997). The cross sections below 275 nm are not very sensitive to temperature over the 226-298 K temperature range, typically < 1%, but the temperature dependence becomes significant above 275 nm. Table 4.4 shows the temperature dependence of these absorption cross sections at longer wavelengths, averaged over the spectral regions shown. 

TABLE 4.3 Ozone Absorption Cross Sections (Base e) ... 

The ozone absorption cross sections are listed in Table V, and the integrated column densities of C>3 above an altitude... 

FIGURE 1 Photodissociation of ozone in the near ultraviolet spectral region. Overlap of solar radiation actinic intensity, ozone absorption cross section, and 0( D) quantum yield to derive the 0( D) production frequency as a function of wavelength. [From Zellner, R., ed. (1999). Global Aspects of Atmospheric Chemistry, Steinkopff/Springer, Darmstadt, Germany.]... 

Fig. 14. Plot of the quantum efficiency for the formation of C>2(v < 26) as a function of wavelength. The value at 193 nm is taken from Stranges et aJ.44 A 10% branching ratio into the triplet channel is assumed. The absorption cross-section for ozone is plotted as the dashed curve on the right-hand axis.

The rate of photolysis, J, depends on the absorption cross-section, a, the number density, the scale height and the angle, all of which are unique properties of a planetary atmosphere. For the Earth and the Chapman mechanism for ozone the O3 concentration maximum is 5 x 1012 molecules cm-3 and this occurs at 25 km, shown in Figure 7.12, and forms the Chapman layer structure. 

As discussed in Chapter 12, the CIO dimer is a central species in the chemistry of the Antarctic ozone hole. Table 4.32 gives the recommended absorption cross sections (DeMore et al., 1997). The photodissociation can, in principle, proceed by two paths ... 

Figures 4.44 and 4.45 show absorption spectra of some simple chlorofluoro-methanes and ethanes, respectively (Hubrich and Stuhl, 1980). Tables 4.37 and 4.38 give the recommended absorption cross sections for some of these compounds (DeMore et al., 1997). None of these compounds absorb in the actinic region above 290 nm, but do around 180-200 nm, wavelengths only found in the stratosphere. As discussed in Chapter 12, it is photolysis at these short wavelengths to generate atomic chlorine that is responsible, along with bromine and perhaps in some cases, iodine atoms, for the chain destruction of stratospheric ozone.

Daumont, D A. Barbe, J. Brion, and J. Malicet, New Absolute Absorption Cross Section of O, in the 195-350 nm Spectral Range, in Ozone in the Atmosphere (R. D. Bojkov and P. Fabian, Eds.), Deepak Publishing, Hampton, VA, 1989. 

Malicet, J., D. Daumont, J. Charbonnier, C. Parisse, A. Chakir, and J. Brion, Ozone UV Spectroscopy. II. Absorption Cross-Sections and Temperature Dependence, J. Atmos. Chem., 21, 263-273 (1995). 

A major advantage of this approach is that the fundamental spectroscopic parameters for OH, including the absorption cross sections for various transitions, are well known (e.g., see Mount, 1992 Dorn et al., 1995b), so that absolute concentrations of OH can be calculated based solely on the absorption spectra. Another major advantage is that the laser beams are expanded so that generation of OH in the beam itself by photolysis of ozone is not the problem that it has been in LIF measurements (vide infra). 

The absorption cross section on the ordinate of the ozone absorption spectrum at the beginning of this chapter is defined by the relation... 

From 200 to 242 nm, the 02 absorption, which is related to the Herzberg continuum with low absorption cross section, occurs in the stratosphere. In this spectral region, the ozone absorption must be introduced since the 03 Hartley band is characterized by high values of the absorption cross section between 200 and 300 nm. The simultaneous absorption by 02 and 03 must be considered in the stratosphere, whereas the O3 absorption is practically negligible in the mesosphere since the total number of absorbing ozone molecules is small. 

Freeman, D.E., Yoshino, K., Esmond, J.R., and Parkinson, W.H. (1984). High resolution absorption cross-section measurements of ozone at 195 K in the wavelength region 240-350 nm, Planet. Space. Sci. 32, 239-248. 

Ozone Photolysis The most important sets of photochemical reactions volve the photolysis of ozone, 03 which occurs over a Table 3 Absorption cross sections of 03 at 273 K [106] in the troposphere in-very broad wavelength... 

The absorption cross sections for O3 at 273 K as recommended by the 2004 JPL/NASA evaluation are given in Table 3 while measured quantum yields (Fig. 1) for ozone photolysis are given in Table 4. In addition, the JPL/NASA evaluation committee has developed an empirical equation for the estimation of the quantum yield for 0( D) as a function of wavelength and temperature (Table 5). 

The absorption cross sections for NO2 and the corresponding quantum yields are given in Table 8 and 9, respectively. The photolysis of NO2 has been investigated intensively over the last 40 years because of its critical role in the formation of ozone in the polluted tropospheric boundary layer [56-63]. The three reactions of Eqs. 33 and 34 form the basis for the photochemical production of ozone. If one considers only these three reactions, then the photo-stationary state (or photochemical steady-state approximation) can be invoked around the oxygen atom as follows ... 

Moortgat G. K., Meller R., aad Schneider W. (1993) Temperature dependence (256-296 K) of the absorption cross sections of bromoform in the wavelength range 285-360 nm. In Tropospheric Chemistry of Ozone in Polar Regions, NATO ASl Ser., Subser. 1 Global Environmental Change (eds. H. Niki and K. H. Becker). Springer, New York, pp. 359-370. 

A large number of laboratory measurements have been reported for the absorption cross sections of ozone (e.g., Inn and Tanaka, 1953 Vigroux, 1969 Molina and Molina, 1986 Daumont et al, 1992 Yoshino et al, 1993), and are the basis for the recommended values presented by WMO (1985) or JPL (1997). High resolution measurements from 195 to 345 nm, and at different temperatures, have been made by Malicet et al. (1995). 

Daumont, D., J. Brion, J. Charbonnier, and J. Malicet, Ozone UV spectroscopy, 1. Absorption cross sections at room temperatures. J Atmos Chem 15, 145, 1992. 

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