The sample is burned in oxygen at 1000°C. Nitrogen oxide, NO, is formed and transformed into NO2 by ozone, the NO2 thus formed being in an excited state NO. The return to the normal state of the molecule is accompanied by the emission of photons which are detected by photometry. This type of apparatus is very common today and is capable of reaching detectable limits of about 0.5 ppm.  [c.29]

Ozone, known for its beneficial role as a protective screen against ultraviolet radiation in the stratosphere, is a major pollutant at low altitudes (from 0 to 2000 m) affecting plants, animals and human beings. Ozone can be formed by a succession of photochemical reactions that preferentially involve hydrocarbons and nitrogen oxides emitted by the different combustion systems such as engines and furnaces.  [c.261]

More precisely, the rate of ozone formation depends closely on the chemical nature of the hydrocarbons present in the atmosphere. A reactivity scale has been proposed by Lowi and Carter (1990) and is largely utilized today in ozone prediction models. Thus the values indicated in Table 5.26 express the potential ozone formation as O3 formed per gram of organic material initially present. The most reactive compounds are light olefins, cycloparaffins, substituted aromatic hydrocarbons notably the xylenes, formaldehyde and acetaldehyde. Inversely, normal or substituted paraffins.  [c.261]

Reactivities compared for selected organic compounds with respect to ozone formation.  [c.262]

To estimate the effect of automobile traffic and motor fuels on ozone formation, it is necessary to know the composition of exhaust gas in detail. Figure 5.26 gives an example of a gas phase chromatographic analysis of a conventional unleaded motor fuel.  [c.262]

For each type of component, its relative reactivity in ozone formation was taken into account which makes it possible to characterize by weighting the behavior of the overall motor fuel under the given experimental conditions. The overall reactivity is in fact governed by a limited number of substances ethylene, isobutene, butadiene, toluene, xylenes, formaldehyde, and acetaldehyde. The fuels of most interest for reducing ozone formation are those which contribute towards minimizing emissions of the above substances.  [c.262]

Example of an analysis of exhaust gas by gas phase chromatography and j relative reactivity of effluents with respect to tropospheric ozone formation. I  [c.263]

Gasolines said to be reformulated are designed with all aspects of environmental protection being considered reducing evaporative losses and conventional exhaust system pollutants, extremely low emissions of toxic substances, the lowest reactivity regarding ozone formation. The general action paths are known reduction of volatility, lowering the levels of aromatics, olefins, sulfur, reducing the distillation end point, addition of oxygenates. Table 5.27 gives an example of a reformulated gasoline s characteristics suggested in 1992 by the Arco Company in the United States. Claims for the pollution improvements are also noted. This is an extreme example of that which would be expected as a result of drastic modification of motor fuel. However, in the United States, local pollution problems observed in a number of urban population centers have already launched safeguarding measures applicable to fuel compositions. These include  [c.264]

Lowi, A. and W.P.L. Carter (1990), A method lor evaluating the atmosphere ozone impact of actual vehicle emissions . SAE paper No. 90-0710, International congress and exposition, Detroit, MI.  [c.457]

Chlorofluorohydrocarbons (CFCs) are good fire fighting agents, but when released cause depletion of the ozone layer, which in turn contributes to global warming. CFG systems are gradually being phased out of the oil and gas industry, and are being replaced by less harmful alternatives.  [c.74]

Quack M and Sutcliffe E 1983 Quantum interference in the IR-multiphoton excitation of small asymmetric-top molecules ozone Chem. Phys. Lett. 99 167-72  [c.1089]

Quack M and Sutcliffe E 1984 The possibility of mode-selective IR-multiphoton excitation of ozone Chem. Phys. Lett. 105 147-52  [c.1089]

This is the source of ozone, tlirough the reaction q, + q. One obtains a pronounced dependence of the  [c.2140]

The chemical reactions in plasmas find applications in tire generation or conversion of gaseous products, primarily via homogeneous reactions or in surface treatment and modification processes via heterogeneous reactions. A classical example for tire production of a gaseous product is tire ozone syntliesis in dielectric barrier discharges. The electrons are the most important species for ozone fonnation [23]. A non-tliennal plasma generated in a dielectric barrier discharge reactor at atmospheric pressure in pure oxygen causes a significant fraction of tire oxygen molecules to be dissociated as the result of electron collisions.  [c.2808]

The ozone fonnation occurs in a three-body collision of O atoms with O2 molecules  [c.2809]

The probability for tliree-body collisions increases with increasing pressure making the use of an atmospheric pressure plasma desirable. The above process is used worldwide for ozone production for water purification.  [c.2809]

The ozone fonnation in the atmosphere is induced by radiation and a result of tliree-body collisions of the oxygen atoms with O2 molecules. This process requires a higher gas density and is, therefore, not efficient in the ionosphere.  [c.2810]

Non-thennal plasmas with their hot electron gas extend the realm of conventional chemistry in many interesting directions. New technical applications have emerged such as surface treatment of materials in plasma etching and thin-film deposition in the microelectronics industry, plasma chemical surface modifications to achieve a variety of desired properties (increased wettability, biocompatibility) and the deposition of various coatings to improve the hardness and the tribological and optical properties of materials. As successfully and widely used as plasma chemistry has been in surface processing applications, the applications of plasma chemical methods for producing gaseous products are limited. The ozone synthesis is a unique process in that category and has been well known for more than a century. The development of new processes for the synthesis or decomposition of gaseous compounds will require a broader as well as a more detailed knowledge of the processes in non-thennal plasma, particularly at higher gas densities, and will necessitate the study of the effect of catalysts on the plasma.  [c.2811]

Ruedenberg and co-workers [33,107], found by exact quantum chemical calculations a crossing point between the two lowest Aj states of ozone. They used the phase-change rule to verify that the electronic wave function changes its sign when transported in a closed loop around this point. This was done by considering the phase change of the dominant configurations of the ground-state wave functions. Initially, only C2v symmetry was considered, later, a complete seam of conical intersections was calculated [107],  [c.382]

Disinfeetion. Chlorine, as gaseous chlorine or as the h5rpochlorite ion, is widely used as a disinfectant. However, its use in some cases can lead to the formation of toxic organic chlorides, and the discharge of excess chlorine can be harmful. Ozone as an alternative disinfectant leads to products that have a lower toxic potential. Treatment is enhanced by ultraviolet light. Indeed, disinfection can be achieved by ultravifflet light on its own.  [c.319]

HOOO(CH2)7COOH. Colourless plates, m.p. lOfi C. Made by the oxidation of oleic acid with ozones.  [c.47]

SCDs (Sulfur Chemiluminescence Detectors) have recently joined the photometric and electrochemical detectors. Upon combustion, sulfur compounds form sulfur monoxide, SO, which reacts with ozone to form a molecule of SO2 in the excited state. The return to the normal molecular state is accompanied by an emission between 300 and 450 nm. It is this emission that is measured and thus allows detection and a selective quantification of sulfur molecules. The detector is very sensitive in theory it responds to a few parts per billion of sulfur. Figure 3.15 illustrates one of the possible uses a chromatogram shown in Figure 3.15a for a gas oil feedstock to a hydrotreating unit and, in Figure 3.15b, for this same gas oil after hydrotreatment. The efficiency of hydrodesulfurization is thus controlled showing the molecules most resistant to desulfurization and allowing modelling studies of the process reactions to be conducted.  [c.76]

Another approach is to use the LB film as a template to limit the size of growing colloids such as the Q-state semiconductors that have applications in nonlinear optical devices. Furlong and co-workers have successfully synthesized CdSe [186] and CdS [187] nanoparticles (<5 nm in radius) in Cd arachidate LB films. Finally, as a low-temperature ceramic process, LB films can be converted to oxide layers by UV and ozone treatment examples are polydimethylsiloxane films to make SiO [188] and Cd arachidate to make CdOjt [189].  [c.562]

It is appropriate that this chapter conclude with a short discussion of a few selected, widely used catalyzed reactions. The reactions chosen—ammonia synthesis, Fischer-Tropsch reactions, ethylene dehydrogenation, the catalytic cracking of hydrocarbons, the oxidation of CO, and photoassisted heterogeneous reactions represent the writers choice of a balanced group of systems of major impact. It is an interesting tribute to the endurance of research problems that the first four systems were chosen in the first, 1960, edition of this booklf Many variations and many new catalysts have appeared since then, of course, and a host of other types of reactions. These range from the catalysis by ice crystals of ozone-depleting reactions to a wide variety of photoas-  [c.728]

Such a sequence of snapshots, calculated in intervals of 4 fs, is shown as a series of double contour line plots on the left-hand side of figure A3.13.11 (tire outennost row shows the evolution of I equation (A3.13.68), the imremiost row is I I equation (A3.13.67), at the same time steps). This is the wave packet motion in CHD for excitation with a linearly polarized field along tlie the v-axis at 1300 cm and 10 TW cm after 50 fs of excitation. At this point a more detailed discussion regarding tlie orientational dynamics of the molecule is necessary. Clearly, the polarization axis is defined in a laboratory fixed coordinate system, while the bending axes are fixed to the molecular frame. Thus, exciting internal degrees of freedom along specific axes in the internal coordinate system requires two assumptions the molecule must be oriented or aligned with respect to the external polarization axis, and this state should be stationary, at least during the relevant time scale for the excitation process. It is possible to prepare oriented states [112. 114. 115] in the gas phase, and such a state can generally be represented as a superposition of a large number of rotational eigenstates. Two questions become important then How fast does such a rotational superposition state evolve How well does a purely vibrational wave packet calculation simulate a more realistic calculation which includes rotational degrees of freedom, i.e. with an initially oriented rotational wave packet The second question was studied recently by frill dimensional quantum dynamical calculations of the wave packet motion of a diatomic molecule during excitation in an intense infrared field [175], and it was verified that rotational degrees of freedom may be neglected whenever vibrational-rotational couplings are not important for intramolecular rotational-vibrational redistribution (IVRR) [ ]. Regarding the first question, because of the large rotational constant of methane, the time scales on which an initially oriented state of the free molecule is maintained are likely to be comparatively short and it would also be desirable to carry out calculations that include rotational states explicitly. Such calculations were done, for instance, for ozone at modest excitations [116. 117], but they would be quite difficult for the methane isotopomers at the high excitations considered in the present example.  [c.1075]

A recent study of the vibrational-to-vibrational (V-V) energy transfer between highly-excited oxygen molecules and ozone combines laser-flash photolysis and chemical activation with detection by time-resolved LIF [ ]. Partial laser-flash photolysis at 532 mn of pure ozone in the Chappuis band produces translationally-  [c.2139]

See pages that mention the term Ozone : [c.311]    [c.23]    [c.27]    [c.73]    [c.93]    [c.95]    [c.293]    [c.294]    [c.294]    [c.294]    [c.294]    [c.261]    [c.262]    [c.264]    [c.264]    [c.526]    [c.899]    [c.1059]    [c.1090]    [c.1240]    [c.1696]    [c.2139]    [c.2139]    [c.2803]   
See chapters in:

Encyclopedia of chemical technology volume 17  -> Ozone

Organic syntheses Acid anhydrides  -> Ozone

Hazardous chemicals handbook Изд.2  -> Ozone

Chemistry of the elements  -> Ozone

Modern inorganic chemistry (1975) -- [ c.262 , c.263 ]

Organic syntheses based on name reactions and unnamed reactions (1994) -- [ c.108 ]

Organic syntheses Acid anhydrides (1946) -- [ c.26 , c.63 ]

Fundamentals of air pollution (1994) -- [ c.0 ]

Hazardous chemicals handbook Изд.2 (2002) -- [ c.16 ]

Chemistry of Organic Fluorine compounds II (1995) -- [ c.0 ]

Chemistry of the elements (1998) -- [ c.3 ]

Introduction to computational chemistry (2001) -- [ c.115 , c.287 ]