Scavenging efficiency

BORS w, HELLER w, MICHEL c and SARAN M (1990) Flavouoids as antioxidants determination of radical-scavenging efficiency Methods in Enzymology 186, 343-55. 

The photolytic reduction of N2 at TiO -suspensions was at first reported by Schrauzer et al. Small amounts of NH3 and N2H4 were obtained as products. The highest activity was found with anatase containing 20-30 % rutile. Very low yields were also obtained with p-GaP electrodes under illumination It is much easier to produce NH3 from NO -solutions at CdS- and Ti02-particles using S -ions as hole scavengers . Efficiencies are not reported yet. Recently the formation of NH3 from NO was observed at p-GaAs electrodes under illumination. In this case NH3-formation was only found in the presence of transition metal ions or their complex with EDTA. 

This equation is particularly useful to derive apparent estuarine water mass ages (Fig. 6) because the term /em is removed. Using ( Ra/ " Ra) isotope ratios in this manner is based on the assumption that the initial ( Ra/ " Ra) activity ratio must remain constant. This conclusion is reasonable as the long-lived parent isotopes ( Pa and Th) have relatively constant activity ratios in sediments, and the intermediate Th isotopes ( Th and Th) are scavenged efficiently in the near-shore water column. The utility of Ra as... 

Fig. 7.11 Scavenging efficiencies of polymer-supported scavengers (a) polystyrene, (b) functionalized silica, (c) plugs, (d) lanterns] at room temperature (left) and under microwave heating (right).

A simple extension of the competition technique is to the comparison of scavenger efficiencies. Thus pairs of spin traps have been allowed to compete for a variety of radicals, including t-butoxyl, phenyl, and primary alkyl. Much more revealing, however, is the type of experiment in which the bimolecular trapping of a radical is allowed to compete with some other reaction of that radical whose absolute rate constant is known. In this way, the rate constant for the trapping reaction itself is accessible. 

The acylation of benzylamine with 4-chlorobenzoyl chloride served as a model reaction to evaluate the efficacy of both of these resins. After removal of both protons and amines the corresponding amide was obtained in 77% yield contaminated with less than 1% benzylamine and acid chloride. The transformation was also performed with commercially available scavenger resins PS-NCO and/or PS-NMM to obtain comparable results, but only approximately half the mass and volume of dendronized resin was required to achieve similar scavenging efficiency. 

Involves converting concentrations to the ratio of an Individual specie to the total concentration of all dissolved species. The data analysis Is then performed on these normalized or relative concentrations. To the degree that an assumption of constant scavenging efficiency holds (each element Is removed from the atmosphere with equal efficiency) relative concentrations might be expected to better reflect the Influence of a pollution source, which, over time might experience differing amounts of dilution by air and water. This technique may produce spurious correlations due to closure (the constant sum) depending on the data structure before normalization ( ). 

With emission source chemical signatures and corresponding aerosol or rainwater sample measurements PLS can be used Co calculate a chemical element mass balance (CEB). Exact emission profiles for the copper smelter and for a power plant located further upwind were not available for calculation of source contributions to Western Washington rainwater composition. This type of calculation Is more difficult for rainwater Chan for aerosol samples due Co atmospheric gas to particle conversion of sulfur and nitrogen species and due Co variations In scavenging efficiencies among species. Gatz (14) has applied Che CEB to rainwater samples and discussed Che effect of variable solubility on the evaluation of Che soil or road dust factor. 

Scavenging efficiency of turkey vultures in tropical forests. Condor 88, 318-323. 

The sources of g(H2) according to deterministic [9] and stochastic [10] modelling are processes (I), (III), and (V) and also the spur reactions (R4) (R5) (R6). As shown in Table 1, the deterministic model indicates that approximately 50% of g(H2) is produced in reactions (R4) and (R5), and similar results are predicted by the stochastic model [10b,20]. The models also predict that the extent of reactions (R4) and (R5) increases with LET. For an increase in LET from 0.2 to 60 eV nm g(H2) increases to 0.27 and 0.42 molecules (100 eV) due to reactions (R4) and (R5), respectively [21]. These data, together with numerous experimental results, are not consistent with the conclusion [17] that H2 is generated mainly through reaction of with H2O. There will, of course, be no produced under conditions where e is scavenged efficiently in sufficiently concentrated solution. However, it does not follow that reactions (R4) and (R5) do not contribute to g(H2) in dilute solution or pure water. 

Bors, W. et al., Elavonoids as antioxidants determination of radical scavenging efficiencies,... 

Bors W, Heller W, Michel C, Saran M. 1990. Flavonoids as antioxidants Determination of radical-scavenging efficiencies. Methods Enzymol 186 343-355. 

Bokkenheuse VD, Shacketon CHL, Winter J. 1987. Hydrolysis of dietaryflavonoide glycosides by strains of intestinal bacteroides from humans. Biochem J 248 953-956. Bors W, Heller W, Michel C, Saran M. 1990. Flavonoids as antioxidants Determination of radical-scavenging efficiencies. In Packer L, Glazer AN, Eds. Methods in Enzymology 186, San Diego Academic Press, pp. 343-355. 

Fig. 7-5. Effect of aerosol particle size on scavenging efficiency of raindrops, falling at an intensity of 1 mm h-1 (redrawn from Rbbig, 1979).

The estimates for wet deposition assume that snow and rain have the same scavenging efficiency, and are based on rain measurements. Only a few studies have examined snow deposition directly.31,39 Earlier field measurements supported the assumption that snow scavenged particulate and vapour PCBs less efficiently than rain.31 However, recent work has examined snow scavenging in greater detail, and concludes that snow is a more efficient scavenger than rain.39... 

Unfortunately, scavengers may considerably reduce the desired effect of radicals for waste treatment. For example, the main natural scavengers of OH are the HCOJ and CO3- ions as well as the humic acids. Their scavenging efficiency for OH can be quite high for example, in a dilute bicarbonate solution (e.g., 15 mM), 98% of the photogenerated OH are scavenged by HCO3. ... 

Caltech unified GCM (Global) Bulk equilibrium, ZSR equation, no hysteresis None Autoconversion nucl. scavenging with prescribed scavenging coefficient for sea-salt and dust and a first-order precipitation-dependent parametrization for other aerosols precip. rate independent of aerosols First-order precipitation-dependent bulk parametrization calculated scavenging efficiency with size dependence Implicitly accounted for in a parametrization of the limiting autoconversion rate... 

Key variables scavenging efficiency, precipitation rate, and sedimentation rate... 

This pattern is different from the model expectation presented by Turekian et al. (1977), which predicted an exponential decrease of Pb flux across the North Pacific. The observations clearly indicate the efficient removal of the burden of Pb from the Asian continent by the time the longitude of Japan is reached. The flux of Pb thereafter is determined by the Rn concentration in the air and the scavenging efficiency by rain. 

An example of a highly efficient interception system is the canopy of a coniferous forest. The large specific surface area of pine and spruce trees exceeds that of broadleaved deciduous trees, giving them a high scavenging efficiency for radioactive aerosol particles. Pine needles have been acknowledged as useful monitors of atmospheric pollution (Eriksson et al., 1989). However, radionuclides will be redistributed in the forest ecosystem due to various removal mechanisms such as rain... 

The OBAC scavenger efficiently removed excess amines (1°, 2°), alcohols (1°, 2 °, allylic, propargylic and benzylic) and thiols after a common benzoylation event,... 

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