Enhancement factor, calculated effect

The net enhancement factor for a droplet consisting of pure water can be as much as 1.6 (Madronich, 1987). Calculations by Ruggaber et al. (1997) suggest that the actinic flux inside cloud drops with a typical size distribution and dissolved particulate matter is more than a factor of two greater than in the cloud interstitial air. This effect of enhanced actinic flux inside droplets may be quite important for aqueous-phase photochemistry in fogs and clouds. 

Indeed, these reactions play an important role in the Antarctic ozone hole and they have important implications for control strategies, particularly of the bromi-nated compounds. For example, Danilin et al. (1996) examined the effects of ClO -BrO coupling on the cumulative loss of O-, in the Antarctic ozone hole from August 1 until the time of maximum ozone depletion. Increased bromine increased the rate of ozone loss under the denitrified conditions assumed in the calculations by converting CIO to Cl, primarily via reactions (31b) and (31c) (followed by photolysis of BrCl). Danilin et al. (1996) estimate that the efficiency of ozone destruction per bromine atom (a) is 33-55 times that per chlorine atom (the bromine enhancement factor ) under these conditions in the center of the Antarctic polar vortex, a 60 calculated as a global average over all latitudes, seasons, and altitudes (WMO, 1999). 

In this respect, the effect of Fe cations on bofh the oxidation rate and complete mineralization rate of phenol and alike aromatic compounds was considered. Optimum conditions were reviewed to use Fe cations as reaction enhancers (henceforth PC reactions involving optimum Fe concentrations are called Fe-assisted PC reactions). This also involved the assessment of effect and mechanism of Fe ions on fhe PC reaction of phenol and other selected aromatic species. A systematic comparison between the kinetic reaction schemes for both unpromoted PC and Fe-assisted PC reactions for the selected model pollutants was also a primary emphasis. Last, the estimation of the enhancement through efficiency factor calculations was described. 

One should keep in mind, however, that (7) and (8) are only approximations for the relation between experimentally determined enhancement factors and probabilities of level populations. The use of these formulae may render comparisons of calculated and observed CIDNP patterns inconclusive unless the relaxation of a multi-level spin system can be described, at least approximately, by a single relaxation time s). To some extent this difficulty may be removed by attributing different relaxation times to different transitions, but even then intramolecular Overhauser effects may still cause deviations of observed from calculated intensity distributions, especially within multiplets Nevertheless, for many applications the approximate formulae (7) to (8) seem adequate. 

Figure 6-31 The enhancement factor t as a function of the effective correlation lime Tc for the standard nuclear Overhauser experiment (NOE) and for the spin-lock, or rotating-coordinate, (ROE) variant. The curves were calculated for an interproton distance of 2.0 A and a spectrometer frequency of 500 MHz, (Reproduced from F. J. M. van de Ven, Multidimensional NMR in Liquids, VCH, New York,...

Figure 2. Calculated effect of buffer alternatives on the liquid-film enhancement factor, 0.1 M CaClt, 55°C, pH 5.5, 3 wM total sulfite, 1000 ppm SOti-...

The enhancement factor involves an atomic physics calculation along the lines as described above for PNC transitions. Because only a nonvanishing effect is sought, the demands on the accuracy of the calculation axe not as stringent, with really only the correct order of magnitude needed. This would of course change were a nonvanishing result to be found, but at present only bounds have been set. The bound from cesium is [65]... 

For practical purpose it is, however, important not only to estimate tire enhancement factor, but also to calculate the impact of mass transfer on the reaction rate occuring on the liquid side of the interface. Defining now the effectiveness factor (liquid utilization factor) as the... 

M.I. Mishchenko, Polarization effects in weak localization of light Calculation of the copolarized and depolarized backscattering enhancement factors, Phys. Rev. B 44, 12,579-12,600 (1991). 

A value of 2.85 x 10 cm /s was obtained. The effective diffusion coefficient for the complex can be calculated from the slope of the enhancement factor plot in Figure 6 using the equation ... 

So far no attention has been given in this chapter on the effect of the diffusivities. Often instantaneous reactions involve ionic species. Care has to be taken in such case to account for the influence of ionic strength on the rate coefficient, but also on the mobility of the ions. For example, the absorption of HCI into NaOH, which can be represented by H + OH HjO. This is an instantaneous irreversible reaction. When the ionic diffusivities arc equal the diffusivities may be calculated from Pick s law. But, H and OH have much greater mobilities than the other ionic species and the results may be greatly in error if based solely on molecular diffusivities. This is illustrated by Fig. 6.3c-2, adapted from Sherwood and Wei s [4] work on the absorption of HCI and NaOH by Danckwerts. The enhancement factor may be low by a factor of 2 if only molecular diffusion is accounted for in the mobility of the species. Important differences would also occur in the system HAc-NaOH. When CO2 is absorbed in dilute aqueous NaOH the effective diffusivity of OH is about twkx that of COj. 

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