Ozone absorption coefficients

Therefore light of wavelength 11,400 A. or less provides enough energy for the dissociation of ozone. Absorption coefficients in the ultraviolet... 

A uniform and consistent set of ozone absorption coefficients is highly desirable, because these data are important in atmospheric problems and quantitative ozone technology. A comparison of the authors results with those of Vigroux should establish a more reliable set of ozone absorption coefficients. 

It is convenient to discuss three regions of the absorption spectrum, separately the Hartley band from 2000 to 3000 A., the Huggins band from 3000 to 3500 A., and the Chappuis band from 4000 to 7500 A. The results of the ozone absorption coefficients measurements are displayed in Figures 2, 3, and 4, respectively. The absorption coefficients measured by the authors are tabulated in Table I. 

Ambient air is sucked through a cell, where the ozone concentration is measured by its UV-absorption at 253.7 nm. At this wavelength the ozone absorption coefficient is close to its maximum. The UV light is produced by a Hg resonance lamp at 253.7 nm and the intensity of the light is measured by a photomultiplier. The ozone concentration is determined fi om the absorbance making use of the law of Lambert Beer ... 

All experimental results should best be evaluated as a function of the specific ozone dose and related data such as the specific ozone absorption and/or consumption. Additionally the ozone yield coefficient, denoting the ratio of ozone absorbed in the liquid (i. e. transferred from the gas) to the DOC removed by ozonation or the total system (cf. Chapter B 1), is often of interest. 

The first quantitative studies were made by Johnston and Crosby,227 228 who used a stopped-flow technique to monitor the disappearance of ozone by absorption of 2537-A light. Intensity was measured with a photomultiplier tube, the output of which was displayed on an oscilloscope with sweep frequency 0.2-2 sec. Corrections were made for the absorption of N204 at 2537 A, because the absorption coefficient of that species is almost 5% that of ozone at that wavelength. The reaction was observed at 198 and 230°K, with initial NO and 03 concentrations of 0.17-1.85 x 10-5 M and 0.27-2.13 x 10 5 M, respectively. Nitrogen was present in pressures of 130-650 torr. The primary step was determined to be a bimolecular second-order reaction... 

Ozonation processes can also be used for determination of mass transfer coefficient. In fact, both ozone absorption in organic-free water, which is a slow gas-liquid reaction, and other ozone gas-liquid reactions have been used for this purpose. For example, Roth and Sullivan [59] and Sotelo et al. [60] determined the mass transfer coefficient from ozone absorption in organic-free water, whereas Ridgway et al. [73] and Beltran et al. [67] carried out similar calculations from ozone absorption in water at pH 2 containing indigo and p-nitrophenol, respectively. 

The solution possesses the characteristic odour and oxidising properties of the gas. In dilute acid solution ozone is much more stable and the absorption coefficient m decinormal sulphuric acid has been experimentally determined as 0 487 at 0.1... 

Solar Radiation. Of all the factors which collectively determine the amount and spectral distribution of the radiation entering a surface layer of the atmosphere, the best established appear to be the spectral irradiance outside the atmosphere and the attenuation by molecular scattering. The absorption coefficients of ozone are well established, but no easy method exists for determining the amount of ozone in a vertical profile of the atmosphere at a given time. The measurement of the particulate content of the atmosphere and its correlation with atmospheric transmission is a field in which much remains to be accomplished. Surprisingly few data exist on the spectral distribution of sky radiation and its variation with solar elevation and atmospheric conditions. The effect of clouds is of secondary importance, as intense smog generally occurs under a clear sky. 

When the authors results on absorption coefficients of ozone in the visible and ultraviolet regions were published (1), a similar set of results appeared in the literature published by Vigroux (3). Prior to this, the results of Ny and Choong ( ) had been accepted as the best available data. The authors results have been adequately compared with these. 

Figure 2. Absorption coefficients of ozone in region of Hartley band, 2000 to 3000 A.

The results of the authors seem more acceptable and are the best values in this region for the absorption coefficient of ozone. 

In the aqueous phase ozone absorbs at 254 nm with a maximum molar absorptivity coefficient 3300 cm Hydroxyl radicals are produced via the ultraviolet photolysis of ozone to produce electronically excited singlet oxygen atoms ... 

Tabulated values of absorption coefficients kos(X) can be found in [5.34] and [5.38]. The relative optical mass of ozone is indicated by o3- It only deviates significantly from mr 70° and can be calculated using a relationship given by N. Robinson [5.41]. 

Figure 4.37 shows the relative contribution of each band to the ozone photolysis frequency as a function of altitude. It should be noted that the value of the ozone photodissociation coefficient depends critically on the absorption by ozone itself, introducing a nonlinear coupling as a function of altitude. The calculation of Jo3 must include the effects of molecular scattering and albedo (see Figure 4.38). 

Ozone can be used as a source for OH radicals since its absorption maximum lies in the UV light range between 240 and 280 nm wavelengths. H2O2 is more efficient in terms of OH radical production per photon absorbed. However, its molar absorption coefficient is lower than that of ozone at these wavelengths, only at lower wavelengths OH radicals are more effectively created [28]. Both combinations have been studied in hterature for the reduction ofMTBE. 

Griggs, M. (1968). Absorption coefficients of ozone in the ultraviolet and visible regions. J. Chem. Phys. 49, 857-859. 

The absorption coefficient of oxygen at 193.1 nm was reported to be 0.0186 cm atm while the quantum yield of ozone formation at 193.1 nm by decomposition of excited oxygen molecules was reported to be 0.3 between 300 and 1300 torr. The low bond strength of ozone and its large absorption... 

The following table lists the molar absorption coefficient of ozone, Ojfg) at 298 K in part of the ultraviolet region. 

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