Ozone extinction coefficient

The first two determinations by radiation absorption require accurate measurements of the extinction coefficients of ozone (a measurement of the absorption efficiency of the incoming radiation at a maximal absorption wavelength) in the ultraviolet and the infrared. Three different principles have been used over the last 20 years to measure the extinction coefficient of ozone in the ultraviolet at 254 nm manometric, decomposition stoichiometry, and gas-phase titration. The manometric method, which is based on pressure measurements of gaseous ozone, requires (in at least one case ) a substantial and somewhat uncertain correction for decomposition and the method of decomposition stoichiometry depends on the pressure change that accompanies the decomposition of ozone to oxygen, 20, 30,. Clyne and Coxon determined ozone... 

DeMore, W. B., and O. Raper. Hartl band extinction coefficients of ozone in the gas phase and in liquid nitrogen, carbon monoxide, and argon. J. Phys. Chem. 68 412-414, 1964. 

A number of investigators have studied the effect of ozone on the ultraviolet absorption spectra of proteins and amino acids. A decrease in the absorption of 280-nm light in a number of proteins was originally reported ly Giese et aV to be a consequence of ozone exposure they suggested that this was due to an interaction of ozone with the ring structures of tyrosine and tryptophan. Exposure of a solution of tryptophan to ozone resulted in a decrease in 280-nm absorption, whereas the extinction coefficient of tyrosine increased. Similar results with tyrosine were reported by Scheel et who also noted alterations in the ultraviolet spectra of egg albumen, perhaps representing denaturation by ozone. 

The typical trace obtained with this instrument (Fig, 7) can be used to explain the operation of the system. The absorbance recorded by the spectrophotometer with both Scrubs turned in is shown as a function of time (the right-hand ordinate is converted to ppm ozone by using an extinction coefficient (22)), Scrub 1 provides a base line for the absorbance (no ozone). At 2 min. Scrub 1 is removed and the absorption rises to a level calculated to be 250-260 ppm of ozone, A 30 second lag occurs due to the volume of the system. The reaction vessel is added to the flow route at U min, and at 8 min Scrub 2 is removed. 

The amount of TBA reactant can be converted into moles of malondialdehyde by the extinction coefficient of 155 mM cm ozone (22), and the yield of this reaction, or ratio of malondialdehyde/ozone taken-up, is shown in Figure 9. Notice that the yield for ozone-treated linolenic acid varies with time of reaction from about 3% to over 30%. These results differ from those for lipid peroxidation reactions which also give rise to malondialdehyde but have yields of 2-5% (23). 

The stoichiometric yield of OH0 is the greatest from the photolysis of hydrogen peroxide. But - as already mentioned - the photolysis of ozone yields more OH0 than that from hydrogen peroxide because of the higher molar extinction coefficient of ozone compared to hydrogen peroxide (see Table 2-3). 

The biologically significant doses of UV radiation at the earth s surface is illustrated in figure 2 for the two cases of PBL. Its variation (daily DNA dose) with visual range and/or total extinction coefficient at 550nm amounts to reductions of 5% and 18% for the two PBL cases. However, these changes may occur in the industrialised NH and not in the pristine SH where stratospheric ozone depletion may be not be counterbalanced by an increase in UV flux attenuating aerosols. 

Reagent III required rapid acidification upon very slow acidification with either ozone or iodate added, iodine losses have been observed. Similar losses occur upon addition of standard iodine to the alkaline reagent before acidification, regardless of the rate of acidification, but not when iodine is added after acidification. Apparently in the former cases iodine is released at the surface of acid drops and absorbed into the surrounding alkali, where the loss occurs. With rapid acidification of samples the iodine extinction coefficient for reagent III agrees well with expected values. 

The determination of ozone in water solution is complicated by the instability of the ozone in solution. Alder and Hill (1) and Stumm (12) showed that ozone in solution is much more stable at low pH values and at temperatures near the freezing point of water, using the absorbance of an ozone solution at 258 to 260 m. The authors repeated the work of Alder and Hill (1) and Kilpatrick, Herrick, and Kilpatrick (8) at pH 2.0 and 1° C. and found the ozone solution completely stable, with no change in absorbance after 8 hours. Under these conditions, an extinction coefficient of 2600 was obtained as compared with 3000 ( ) and 1000 (1). 

It was assumed that I/Iq, the per cent transmittance, may be used in the kinetic equations instead of C, the concentration of carbonyl, because the film thickness, d, and the extinction coefficient, e, remain constant. Plots of log I/Iq) vs. time of ozonization showed that the reaction had a very high initial rate of oxidation which... 

Ozone in the aqueous phase was analyzed by the indigo method of Bader and Holgne (28,29). using the dlsulfonate rather than the trisulfonate as originally described by those authors. This method (hereafter called the HBI method) was calibrated in purified water against the lodlmetrlc method of Flamm ( ) (BKI) and checked by UV absorbance using the extinction coefficient of Hart et al. (3D. 

Spectroscopy in the ultraviolet and visible range has been used to follow the evolution of NO2 in order to study the autoxidation kinetics (29), and symmetric NO3 has been characterized by the method already in the early twentieth century (5,48) it can be prepared in easily detectable quantities by the reaction of N2O5 or NO2 with ozone. It is, however, not very fikely an intermediate of NO autoxidation, because its formation would require the splitting of02, and because the electrode potential ofits reduction to NOs" has been estimated to be higher than 2 V, which would lead to side reactions that would have been hardly overlooked. In contrast, the electronic spectrum of ONOO is not known, and it would most likely not be helpfijl in detecting it at steady-state concentrations, since known extinction coefficients of N-O compounds in the visible and near ultraviolet spectrum are all below 1000 cm Thus, the absorption of ONOO during autoxidation would vanish under the contribution of the product, NO2. ... 

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