Water, distribution photolysis

DBCP. The predictions suggest that DBCP is volatile and diffuses rapidly into the atmosphere and that it is also readily leached into the soil profile. In the model soil, its volatilization half-life was only 1.2 days when it was assumed to be evenly distributed into the top 10 cm of soil. However, DBCP could be leached as much as 50 cm deep by only 25 cm of water, and at this depth diffusion to the surface would be slow. From the literature study of transformation processes, we found no clear evidence for rapid oxidation or hydrolysis. Photolysis would not occur below the soil surface. No useable data for estimating biodegradation rates were found although Castro and Belser (28) showed that biodegradation did occur. The rate was assumed to be slow because all halogenated hydrocarbons degrade slowly. DBCP was therefore assumed to be persistent. 

In contrast, photolysis of methoprene in true aqueous solution gave a simpler distribution of different products (40). Five major products (25, 11, 13, 13, and 8% yield) were separated, but could not be positively identified due to lack of sufficient quantity (methoprene water solubility = 1.4 mg/1) and the singularly uninformative mass spectral fragmentations of the products. 

Comparing the yields for the different reaction channels of bare PA with hydrated PA, it can be seen that there is a change in the distribution of the yields of different channels. However, there is no clear trend on the yields as a function of the number of water molecules. This is also observed experimentally the experiment shows no significant photolysis suppression by the solvent. 

In Section 21.1 we discussed the simultaneous influence of transport and transformation processes on the spatial distribution of a chemical in an environmental system. As an example we used the case of phenanthrene in the surface water of a lake. In Fig. 212b two situations were distinguished which differed by the relative importance of the rate of vertical mixing versus the rate of photolysis. Yet, neither was a quantitative method given to calculate the resulting vertical concentration profile (profiles 1 and 2 in Fig. 21.26), nor did we explain how the rates of such diverse mechanisms as diffusion, advection, and photolysis should be compared in order to calculate their relative importance. In this section we will develop the mathematical tools which are needed for dealing with such situations. 

The flash photolysis of water in this region has produced OH(X2n), which according to Welge and Stuhl (1033), is rotationally excited only up to N" = 5 and no vibrational excitation is found. The rotational distribution of OH is practically equal to that at room temperature, suggesting that the excess energy, the difference between hv and D0(H—OH), is distributed between translational energies of H and OH [also see Masanet et al. (241, 665)]. The excited state of water responsible for dissociation in this region is considered to be the unstable A( B,) state [Horsley and Fink (485), Miller et al. (704)]. 

Figure 6. Hydrogen production at 25°C in deaerated solutions as a function of catalyst (rhodium) concentration during the first two hours of irradiation using 350 nm cut-off and water filters. Plotted are the amount of hydrogen produced in 25 ml DHP vesicle solution.and measured in the gas phase (16 ml) by GC s 2 x 10- J M DHP, 2 x 10 M CdS symmetrically distributed on both sides of the vesicles, and 10 J M PhSH as electron donor pH approximately 7 at sonication and during photolysis. Concentrations of the catalyst, reduced by uv irradiation prior to visible light photolysis ( - Dl 1 ° ...

Schinke, R., Engel, V., and Staemmler, V. (1985). Rotational state distributions in the photolysis of water Influence of the potential anisotropy, J. Chem. Phys. 83, 4522-4533. 

In this section the environmental distribution of PCAs will be estimated using Mackay s Equilibrium Criterion (EQC) level III fugacity model [79]. Level III refers to a steady state, nonequilibrium system among soil, air, and water compartments, with the chemical undergoing reactions or inputs and removal processes (advection, volatilization, deposition, photolysis, hydrolysis, and biodegradation). 

It has been suggested that their low results were due to the presence of water vapor (51) or long-wavelength contaminant emission (52). The importance of water vapor has been demonstrated by Loucks and Cvetanovic (53), who showed that a satisfactory material balance could be obtained in CO2 photolysis at 153.3 nm if O3 production was considered. The product distribution was changed substantially in the presence of water vapor. 

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