Effects of halocarbons

Yamazaki H, Yamaguchi T, Yamaguchi A, et al. 1992. Effect of halocarbons and styrene on thrombin and calcium ionosphere induced activation of rabbit platelets. Chemosphere 25 665-673. 

It seems likely that further kinetic studies and modeling investigations, as well as mudi accelerated research on alternative halocarbons, will be required before a complete solution of the ozone-depletion theory is at hand. For instance, the role of chlorine nitrate, QONOi, has recently been discussed. This molecule can act as an additional QO sink reaction, leading to a reduction in the effect of halocarbons on ozone depletion. 

The choice of the solvent also has a profound influence on the observed sonochemistry. The effect of vapor pressure has already been mentioned. Other Hquid properties, such as surface tension and viscosity, wiU alter the threshold of cavitation, but this is generaUy a minor concern. The chemical reactivity of the solvent is often much more important. No solvent is inert under the high temperature conditions of cavitation (50). One may minimize this problem, however, by using robust solvents that have low vapor pressures so as to minimize their concentration in the vapor phase of the cavitation event. Alternatively, one may wish to take advantage of such secondary reactions, for example, by using halocarbons for sonochemical halogenations. With ultrasonic irradiations in water, the observed aqueous sonochemistry is dominated by secondary reactions of OH- and H- formed from the sonolysis of water vapor in the cavitation zone (51—53). 

The effects of small halocarbons, such as chloroform, bromoform, and carbon tetrachloride, on several RO membranes have been considered (61). 

Fluorinated organic compounds often may seem abnormal m comparison with hydrocarbon or other halocarbon compounds, but their behavior usually is quite intelhgible and predictable when the effects of fluonnation on molecular properties are understood This chapter discusses these charactenstic effects... 

Electrochemical methods are available for the direct dehalogenation of organic halides to a limited extent fluorides and monochlorides are generally not reducible [1], In the presence of transition-metal complexes as mediators (Med), however, the electrolysis of halocarbons (RX) can be performed more effectively and selectively under various conditions [155-158]. Mediated electroreduction is most efficient when the electron transfer step E° (Med/Med -) is more negative than E° (RX/RX -) [157] (cf. Section 18.4.1). 

Trochimowicz, H.J., C.F.Reinhardt, L.S.Mullin, and B.W.Karrh. 1976. The effect of myocardial infarction on the cardiac sensitization potential of certain halocarbons. J. Occup. Med. 18 26-30. 

Time scaling Not applied. Effects such as cardiac sensitization have been correlated with blood concentrations. Several studies have shown that blood concentrations of halocarbons do not increase greatly with time after 15 min of exposure. The key study showed that at each exposure concentration, blood ... 

Abrahamsson K, Choo KS, Pedersen M, Johansson G, Snoeijs P (2003) Effects of temperature on the production of hydrogen peroxide and volatile halocarbons by brackish-water algae. Phytochemistry 64 725-734... 

This report deals primarily with the origins and effects of ozone and other photochemical oxidants. It is limited, more or less, to the problem of urban pollution and to such closely related topics as natural background in the earth s boundary layer. No consideration is given to the stratospheric ozone layer and the effects produced by supersonic transport (sst) emission or halocarbons. 

The role of biomass in the natural carbon cycle is not well understood, and in the light of predictions of a future atmospheric energy balance crisis caused by carbon dioxide accumulation, in turn the result of an exponential increase in the consumption of carbon fuel, the apparent lack of concern by scientists and policy makers is most troubling. Yet there is no other single issue before us in energy supply which will require action long before the worst effects of excess production will be apparent. The only satisfactory model is the action taken by the R D community with respect to the SST in nitric oxide potential and chloro-halocarbon emissions, when it was realised that the stratospheric ozone layer was vulnerable to interference. Almost all other responses to pollution" have been after definitive effects have become apparent. 

A study is being conducted by R.G. Schnellmann (University of Georgia) for the National Institute of Environmental Health Sciences to evaluate the mechanism of nephrotoxicity of halocarbons, including hexachlorobutadiene. The mechanism of how metabolites alter proximal tubular cellular physiology to produce toxicity is being investigated, with particular emphasis on the effects of metabolites on mitochondria (CRISP 1993). 

Figure 14.25 illustrates the estimated relative contributions to the direct heating effect and to the indirect cooling effect in 1990 and 2040, respectively (Daniel et al., 1995). The enhanced impact of the halons on cooling is particularly apparent. The net contribution of halocarbons through about 2080 is still estimated by Daniel et al. (1995) to be significant, however, in the range of 0.15-0.25 W m 2. 

In searching for chemical methods of destroying organic pollutants, chemists tend to look to oxidative methods, since the preferred end product is usually C02, but, as discussed below, special methods are usually necessary to bring about oxidation to acceptable products. In 1995, however, it was shown that elemental (zero-valent) metals such as ordinary iron filings can be effective in the reductive conversion of halocarbon pollutants such as trichloroethene in wastewater to innocuous hydrocarbons over a few days14 ... 

HF is extremely stable and accumulates in the Middle Atmosphere. Its present abundance is equivalent to the accumulated fluorine amount liberated from fluorine bearing halocaibons up to present, and it increases at the pace of ongoing fluorine species entering the stratosphere. As HF is not a natural atmospheric constituent, the HF budget of the Middle Atmosphere is an important piece of evidence showing the fate and effect of fluorinated halocarbons. 

Halocarbons, a class of polar solvents, are hydrocarbons with an attached halogen. There are commonly three types of halocarbon solvents those based on chlorine, fluorine, and a combination of the two. They are all powerful degreasing materials and can be particularly effective in removing polar contaminants from glass. The chlorofluorocarbons are currently under review because they cause environmental damage to the ozone layer.1... 

Abstract. Destructive adsorption of halocarbons on nanocrystalline oxides has been studied. The effect of nanoparticle size and phase composition on the reaction kinetics is discussed. The reactivity of nanocrystalline oxides has been found to increase after deposition of a permeable carbon coating. The possibility of synthesis of new nanocrystalline halogenated materials using nanoscale oxides as precursors has been demonstrated. 

EFFECT OF CARBON COATING ON AP-MGO REACTIONS WITH HALOCARBONS... 

We are not yet sure what causes the positive effect of the carbon coating on the performance of AP-MgO in the reactions with halocarbons. The carbon coating may adsorb some of the reaction products or impurities in the feed, that allows for a faster reaction of the halocarbons with the oxide core. Further studies including mass-spectrometric analysis of the gas phase composition are required. 

There is growing evidence that the composition of the troposphere is changing. For example, analysis of historical ozone records has indicated that tropospheric ozone levels in both hemispheres have increased by a factor of 3-A over the last century. Methane concentrations have effectively doubled over the past 150 years and N2O levels have risen by 15% since pre-industrial times.Measurements of halocarbons have shown that this group of chemically and radiatively important gases to be increasing in concentration until relatively recently. 

Under the agreements of the Montreal Protocol on Substances that Deplete the Ozone Layer, the production of chlorofluorocarbons (CFCs), halons and several other halocarbons has been prohibited [1,2]. Consequently, there is an interest in replacing these compounds [3]. As part of the development of such replacing compounds, it is necessary to consider and evaluate the potential environmental effects of their use, especially on stratospheric ozone [2],... 

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