Ozone formation


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]

O3 + /i2 — O2 + O. When visible light is above 400 nm, only ground-state oxygen molecules (3 g and oxygen atoms ( P) are formed (22). The initiation step is followed by ozone formation and destmction reactions, O + Og + M— Og+M and O3 +0— 2 02. At - 600 nm, the maximum quantum yield, O, is 2.0 mol/bv.  [c.491]

Ozone can react rapidly with NO to produce NO2, which re-enters the ozone formation cycle O3 + NO — O2 + NO2. This is the main ozone-depleting reaction in the absence of sunlight. Ozone also reacts with NO2 (to form NO, which in turn reacts with NO2 to form N20 ), as  [c.497]

Electrical Characteristics. The basic features of an electric discharge ceH are depicted in Eigure 2. Electrical energy to the ozone generator is provided by a power supply, a frequency converter, and a transformer. Ozone formation is directiy proportional to the power consumed in the discharge at constant concentration, temperature, and pressure. The average discharge power consumption P (W) is given by (96)  [c.498]

Energy Requirements and Efficiency. The thermodynamics of ozone synthesis require the expenditure of 142.7 kj/mol (34.1 kcal/mol) thus the formation of 1 kg of ozone requires 2.97 MJ (711 kcal) or 0.85 kWh/kg at 100% efficiency. The more concentrated the ozone, the higher the specific energy (kWh/kg) and the lower the efficiency. The specific energy for ozone production from dry oxygen varies from 7—14 kWh/kg over the 1—6 wt % range. For dry air, the specific energy (15—22 kWh/kg for 0.5—3.0 wt % ozone) is lower than expected due to the contribution of atomic nitrogen to ozone formation. The higher-than-theoretical specific energy requirements are due to the fact that most of the suppHed energy is converted to heat resulting from ozone formation and decomposition reactions. These specific energy requirements correspond to ozone synthesis efficiencies from oxygen and air of 6—12% and 4—6%, respectively. Thus, the portion of the input synthesis energy dissipated as heat is 88—94% for oxygen and 94—96% for air. In addition to the power requirements for the ozone generator, the air-preparation unit requires 4.4—7.7 (kWh)/kg ozone, and the oxygen-recycle unit an additional 2—7 (kWh) /kg ozone.  [c.499]

Ozone Generator Design. A better understanding of discharge physics and the chemistry of ozone formation has led to improvements in power density, efficiency, and ozone concentration, initiating a trend toward downsizing.  [c.499]

Title IX of the Clean Air Act Amendments of 1990 addresses air poUution research areas including monitoring and modeling, health effects, ecological effects, accidental releases, pollution prevention and emissions control, acid rain, and alternative motor vehicle fuels. The provisions require ecosystem studies on the effects of air pollutants on water quality, forests, biological diversity, and other terrestrial and aquatic systems exposed to air pollutants mandate the development of technologies and strategies for air pollution prevention from stationary and area sources and call for several major studies. The EPA must improve methods and techniques for measuring individual air pollutants and complex mixtures and conduct research on long- and short-term health effects, including the requirement for a new interagency task force to coordinate these research programs. Finally, the Agency must develop improved monitoring and modeling methods to increase the understanding of tropospheric ozone formation and control.  [c.405]

Toxicity. Inhalation or ingestion of toluene can cause headaches, confusion, weakness, and memory loss. Toluene may also effect the way the kidneys and liver function. Reactions of toluene in the atmosphere contribute to ozone formation. Ozone can affect the respiratory system, especially in sensitive individuals such as asthma or allergy sufferers. Unborn animals were harmed when high levels of toluene were inhaled by their mothers, although the same effects were not seen when the mothers were fed large quantities of toluene. Note that these results may reflect similar difficulties in humans. Carcinogenicity, There is currently no evidence to suggest carcinogenicity.  [c.107]

Southern Oxidant Study (SOS) a study to assess the sources and transport of air pollutants contributing to ozone formation.  [c.548]

Ozon, n. ozone, -bildung, /. ozone formation.  [c.330]

Onroad and off-road heavy-duty vehicles (greater than 8,500 pounds gross vehicle weight rating) contribute significantly to emissions of NO which in turn participate in ozone formation. As one would expect, heavy-duty engines are large, and the engine load for a vehicle can-ymg a 60,000-pound payload is extremely high. Most heav -duty trucks operate on the diesel cycle, an engine cycle that produces much higher temperature and pressure conditions, leading to the formation of significantly greater NO levels per mile traveled. Given the stringent controls implemented for light-duty vehicles, it is not surprising that the heavy-duty vehicle contribution as a percentage of regional emissions has been increasing. Projections for the Los Angeles basin in 2010 indicate that without further controls, heavy-duty vehicles will contribute more than 55 percent of onroad NO emissions.  [c.454]

The adherence of mercury to glass, i.e. tailing in presence of ozone, is probably due to the formation of an oxide. The oxidation of the iodide ion to iodine in solution is used to determine ozone quantitatively.  [c.264]

Tests demonstrate that methanol vehicles can meet stringent emission standards for HC, CO, and NO as indicated in Figure 2. The primary benefit of methanol, however, is not the amount of hydrocarbons emitted but rather that methanol-fueled vehicles emit mainly methanol which is less reactive in the formation of ozone than the variety of complex organic molecules in gasoline exhaust. Formaldehyde [50-00-0] emissions from methanol vehicles are increased in comparison to gasoline vehicles. Tests of 1983 Escorts showed tailpipe levels as high as 62 mg/km, well above typical gasoline levels of 2 to 7 mg/km. The 1981 Rabbits ranged from about 6 to 14 mg/km and the 1981 Escorts had levels less than 7 mg/km. AH results were obtained on relatively low mileage vehicles. Deterioration of catalyst effectiveness could increase these emissions.  [c.425]

Perfluorinated ethers and perfluorinated tertiary amines do not contribute to the formation of ground level ozone and are exempt from VOC regulations (32). The commercial compounds discussed above have an ozone depletion potential of zero because they do not contain either chlorine or bromine which take part in catalytic cycles that destroy stratospheric ozone (33).  [c.298]

Emissions from methanol vehicles are expected to produce lower HC and CO emissions than equivalent gasoline engines. However, methanol combustion produces significant amounts of formaldehyde (qv), a partial oxidation product of methanol. Eormaldehyde is classified as an air toxic and its emissions should be minimized. Eormaldehyde is also very reactive in the atmosphere and contributes to the formation of ozone. Emissions of NO may also pose a problem, especiaHy if the engine mns lean, a regime in which the standard three-way catalyst is not effective for NO reduction.  [c.195]

Oxidation. Maleic and fumaric acids are oxidized in aqueous solution by ozone [10028-15-6] (qv) (85). Products of the reaction include glyoxyhc acid [298-12-4], oxalic acid [144-62-7], and formic acid [64-18-6], Catalytic oxidation of aqueous maleic acid occurs with hydrogen peroxide [7722-84-1] in the presence of sodium tungstate(VI) [13472-45-2] (86) and sodium molybdate(VI) [7631-95-0] (87). Both catalyst systems avoid formation of tartaric acid [133-37-9] and produce i j -epoxysuccinic acid [16533-72-5] at pH values above 5. The reaction of maleic anhydride and hydrogen peroxide in an inert solvent (methylene chloride [75-09-2]) gives permaleic acid [4565-24-6], HOOC—CH=CH—CO H (88) which is useful in Baeyer-ViUiger reactions. Both maleate and fumarate [142-42-7] are hydroxylated to tartaric acid using an osmium tetroxide [20816-12-0]/io 2LX.e [15454-31 -6] catalyst system (89).  [c.452]

With 334-nm uv radiation, the decomposition mechanism is similar to that with red light, except that the maximum quantum yield is four (in the absence of O2) due to the formation of singlet delta oxygen ( g) which decomposes ozone (29). At 313 and 254 nm, a chain decomposition occurs with a maximum O of 6 (30,31). The primary step involves photodissociation of ozone to produce an excited oxygen atom ( D) and a singlet delta oxygen molecule ( g)- Reaction of oxygen atoms with molecular oxygen produces singlet sigma oxygen molecules ( as well as ground-state ( P) oxygen atoms. The energetic, electronically excited singlet oxygen molecules can decompose ozone and Og and ) + O3 —> 2 Og + O (32). Reaction of  [c.491]

Formation of Hydrogen Tetroxide. The reaction of hydrogen atoms withHquid ozone at — 196°C proceeds through the intermediate formation of hydroperoxyl radicals forming hydrogen tetroxide, which decomposes on warming to produce equimolar amounts of and O2 (53).  [c.493]

Kinetics and Mechanism of Ozone Reactions. Ozone attacks nucleophilic centers, ie, points of high electron density, in organic substrates. Reactivity of potential reaction sites is enhanced by the presence of electron-donating groups such as CH, and decreased by electron-withdrawing groups such as C=0, COOH, Cl, and NO2. Reaction products depend on solvent type (reactive or nonreactive) and ozonation conditions. Ozone does not totaHy mineralize, ie, convert to CO2 and water, most organic compounds during water treatment. Except in rare cases, such as the oxidation of formate, only partial oxidation is achieved on account of the low reactivity of common intermediate oxidation products, eg, acetic and oxaHc acids. Although ozone has a high thermodynamic oxidation potential, its effectiveness in water treatment depends on the kinetics of its reactions, which can vary widely indeed, rate constants can vary over 14 orders of magnitude, from for acetic acid to 10 L/(mol-s) for phenolate ion (56).  [c.493]

The C—F bonds also are cleaved, resulting ultimately in the formation of HF, a stable fluorine reservoir. The Cl (or Br) atoms formed can convert ozone to oxygen catalyticaHy indeed, one chlorine atom is capable of destroying thousands of ozone molecules. Although much less abundant in the stratosphere than chlorine, bromine is considerably more reactive in some reactions, thus accounting for a significant fraction of ozone destmction in certain catalytic cycles. SateUite and airborne observations have shown significant decreases in total column ozone since 1978, ranging from zero near the equator to 6—8%  [c.495]

Most ozone is formed near the equator, where solar radiation is greatest, and transported toward the poles by normal circulation patterns in the stratosphere. Consequendy, the concentration is minimum at the equator and maximum for most of the year at the north pole and about 60°S latitude. The equihbrium ozone concentration also varies with altitude the maximum occurs at about 25 km at the equator and 15—20 km at or near the poles. It also varies seasonally, daily, as well as interaimuaHy. Absorption of solar radiation (200—300 nm) by ozone and heat Hberated in ozone formation and destmction together create a warm layer in the upper atmosphere at 40—50 km, which helps to maintain thermal equihbrium on earth.  [c.495]

Because ozone formation occurs only within these microdischarge channels, ozone-production efficiency for the most part depends on the strength of the microdischarges, which is influenced by a number of factors such as the gap width, pressure, properties of the dielectric and metal electrode, power  [c.497]

In practice, precipitators are usually operated at the highest voltage practicable without sparking, since this increases both the particle charge and the electrical precipitating field. The sparking potential is generally higher with a negative charge on the discharge electrode and is less erratic in behavior than a positive corona discharge. It is the consensus, however, that ozone formation with a positive discharge is considerably less than with a negative discharge. For these reasons negative discharge is generally used in industrial precipitators, and a positive discharge is utihzed in air-conditioning applications. In Table 17-13 are given some typical values for the sparldng potential for the case of small wires in pipes of various sizes. The sparking potential varies approximately directly as the density of the gas but is very sensitive to the character of any material collected on the electrodes. Even small amounts of poorly conducting material on the electrodes may markedly lower the sparking voltage. For positive polarity of the discharge electrode, the sparking voltage will be very much lower. The sparking voltage is greatly affected by the temperature and humidity of the gas, as sEown in Fig. 17-6.5.  [c.1610]

Selective Catalytic Reduction of Nitrogen Oxides The traditional approach to reducing ambient ozone concentrations has been to reduce VOC emissions, an ozone precurssor. In many areas, it has now been recognized that ehmination of persistent exceedances of the National Ambient Air Qnality Standard for ozone may reqnire more attention to reductions in the other ingredients in ozone formation, nitrogen oxides (NOJ. In such areas, ozone concentrations are controlled by NO rather than VOC emissions.  [c.2195]

The reactivity of chemical compounds will differ because of their structure and molecular weight. Hydrocarbon compounds have been ranked according to their rate of reaction wifh various types of oxidizing species such as OH, NO3, and O3 (1). The role of hydrocarbons, along with oxides of nitrogen, in the formation of ozone is very complex. Ozone formation is a function of the mixture of hydrocarbons present and the concentration of NOj, [NO ] (= [NO] -f- [NO2]). The concept of an incremental reactivity scale permits accessing the increment of ozone formation per incremental change in a single hydrocarbon component (2). Incremental reactivity is determined by calculating the ozone formation potential in a baseline sce nario using a simple mixture of hydrocarbons representing an urban atmosphere. Then for each hydrocarbon species of interest, the ozone formation is recalculated with incremental hydrocarbons added to the mixture. From this approach, the A[03]/A[HC] values represent the impact of a specific hydrocarbon on urban photochemical smog formation.  [c.166]

Approaches used to model ozone formation include box, gradient transfer, and trajectoty methods. Another method, the particle-in-cell method, advects centers of mass (that have a specific mass assigned) with an effective velocity that includes both transport and dispersion over each time step. Chemistry is calculated using the total mass within each grid cell at the end of each time step. This method has the advantage of avoiding both the numerical diffusion of some gradient transfer methods and the distortion due to wind shear of some trajectory methods.  [c.330]

Gulf of Maine Oxidant Study (GOMOS) a study to investigate the sources and transport of pollutants contributing to ozone formation.  [c.531]

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]

Once the sun sets, O formation ceases and, in an urban area, ozone is rapidly scavenged by freshly emitted NO (eq. 3). On a typical summer night, however, a nocturnal inversion begins to form around sunset, usually below a few hundred meters and consequently, the surface-based NO emissions are trapped below the top of the inversion. Above the inversion to the top of the mixed layer (usually about 1500 m), O is depleted at a much slower rate. The next morning, the inversion dissipates and the O -rich air aloft is mixed down into the O -depleted air near the surface. This process, in combination with the onset of photochemistry as the sun rises, produces the sharp increase in surface shown in Figure 1. As shown, the overnight depletion is less in the more mral areas than in a large urban area such as New York City. This is a result of the lower overnight levels of NO in mral areas. Even in the absence of NO or other O scavengers (olefins, for example), O decreases at night near the ground faster than aloft because of its destmction at any surface, ie, the ground, buildings, trees. At the remote mountaintop sites, Whiteface and Utsayantha, there is no overnight decrease in O concentrations.  [c.370]

Concern arose during the 1970s about cumulative CFG emissions iato the atmosphere with progressive depletion of the stratospheric ozone layer by Cl atoms and led to the formation and global support of a multinational fomm, called the Montreal Protocol on Substances That Deplete the Ozone Layer. As a result, CFG production has been dramatically decreased and will likely be totally phased out before the year 2000 (3) (see Fluorinated aliphatics compounds). If hydrogen atoms are introduced into the CFG stmcture to lower the chlorine content, the resulting hydrochlorofluorocarbon (HCFC) is more susceptible to degradation in the lower atmosphere before it can reach the stratosphere. However when a hydrogen atom is introduced into a one-carbon compound, the boiling point is lowered and may be too low for the same CFG appHcation. Therefore two-carbon compounds bearing some hydrogen are more attractive substitutes than the one-carbon modified CFCs. As hydrogen content increases, there is a counter effect of increasing flammabihty, which in turn limits some HCFC appHcations.  [c.266]

Oxidative Ring Opening. Many oxidizing reagents, such as peracids, ozone [10028-15-6] or Fel2, are suitable for oxidative deamination of aziridines to give olefins (18). On the other hand, oxidation of bicycHc 2,3-polymethyleneaziridines with lead tetraacetate leads to retention of the nitrogen ia the molecule with the formation of CO-keto nitriles (338).  [c.11]

Hydrogen peroxide greatly accelerates the decomposition of ozone in alkaline solutions because of formation of HOg, which reacts rapidly with ozone to form the radical ion (25). When the concentration of H2O2 exceeds 10 Af, the decomposition of ozone is initiated faster by HOg than by  [c.491]

Sulfur Compounds. Aqueous sulfide and H2S, an odiferous compound in some waters, are oxidized rapidly (initially to sulfite and sulfurous acid) the rate constants ate 3x10 and 3 X 10 , respectively. Thiocyanate is oxidized by ozone to cyanide and sulfate via the intermediate formation of sulfite (47).  [c.492]

Formation of Hydrogen Trioxide. Formation of hydrogen trioxide, HOOOH, has been observed as a transient intermediate in the ozonation of various organic molecules. For example, ozonation of 2-ethylanthrahydroquinone at —78° C produces an organic hydrotrioxide and hydrogen trioxide in - 40% yield (52). Hydrogen trioxide decomposes by first-order kinetics beginning at about —40° C, forming water and singlet delta oxygen in its reactions, hydrogen trioxide is even more electrophilic than ozone.  [c.493]


See pages that mention the term Ozone formation : [c.262]    [c.885]    [c.495]    [c.497]    [c.26]    [c.32]    [c.261]    [c.264]    [c.526]    [c.101]    [c.495]   
Fundamentals of air pollution (1994) -- [ c.166 , c.246 ]