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Production, photochemical smog

Nitrogen Oxides. From the combustion of fuels containing only C, H, and O, the usual ak pollutants or emissions of interest are carbon monoxide, unbumed hydrocarbons, and oxides of nitrogen (NO ). The interaction of the last two in the atmosphere produces photochemical smog. NO, the sum of NO and NO2, is formed almost entkely as NO in the products of flames typically 5 or 10% of it is subsequently converted to NO2 at low temperatures. Occasionally, conditions in a combustion system may lead to a much larger fraction of NO2 and the undeskable visibiUty thereof, ie, a very large exhaust plume. [Pg.529]

The important hydrocarbon classes are alkanes, alkenes, aromatics, and oxygenates. The first three classes are generally released to the atmosphere, whereas the fourth class, the oxygenates, is generally formed in the atmosphere. Propene will be used to illustrate the types of reactions that take place with alkenes. Propene reactions are initiated by a chemical reaction of OH or O3 with the carbon-carbon double bond. The chemical steps that follow result in the formation of free radicals of several different types which can undergo reaction with O2, NO, SO2, and NO2 to promote the formation of photochemical smog products. [Pg.174]

Combustion processes are the most important source of air pollutants. Normal products of complete combustion of fossil fuel, e.g. coal, oil or natural gas, are carbon dioxide, water vapour and nitrogen. However, traces of sulphur and incomplete combustion result in emissions of carbon monoxide, sulphur oxides, oxides of nitrogen, unburned hydrocarbons and particulates. These are primary pollutants . Some may take part in reactions in the atmosphere producing secondary pollutants , e.g. photochemical smogs and acid mists. Escaping gas, or vapour, may... [Pg.502]

VOCs react in the presence of sunlight to produce photochemical smog, a mixture of organic chemicals that can irritate the eyes and other mucous membranes. VOCs also constitute a major precursor chemical leading to ozone production. VOC levels across the United States fell, on average, by 20.4 percent between 1989 and 1998. [Pg.49]

C05-0120. Explain in your own words how the reactions occurring in the cylinders of automobile engines contribute to the production of photochemical smog. Use balanced equations when appropriate. [Pg.345]

Basic rate information permits one to examine these phenomena in detail. Leighton [2], in his excellent book Photochemistry of Air Pollution, gives numerous tables of rates and products of photochemical nitrogen oxide-hydrocarbon reactions in air this early work is followed here to give fundamental insight into the photochemical smog problem. The data in these tables show low rates of photochemical consumption of the saturated hydrocarbons, as compared to the unsaturates, and the absence of aldehydes in the products of the saturated hydrocarbon reactions. These data conform to the relatively low rate of reaction of the saturated hydrocarbons with oxygen atoms and their inertness with respect to ozone. [Pg.412]

Three properties of photochemical smog were evident first in Los Angeles eye irritation haze (aerosol) formation and the d adation of rubber products. All three are associated with oxidants, although aerosols can also be formed by other pollutants, particularly sulfur dioxide. [Pg.14]

TABLE 6-1 Substances and Monitoring Practices for Species Present in Photochemical Smog as Precursors or Products... [Pg.240]

The interplay of HO, peroxy radicals, VOCs, and NO , species has substantial implications for tropospheric air quality. For instance, VOCs, NO , , and sunlight result in poor visibility from ozone and aerosol formation, together denoted as photochemical smog, which can lead to adverse health effects in sensitive individuals. Normally, we think of minimizing either class of compounds as beneficial to the atmosphere. However, minimizing VOC emissions only impacts ozone concentration in high-NO , areas. Moreover, in VOC-sensitive areas, reductions in NO , may lead to the overproduction of ozone. We can examine a simplified scheme for ozone production ... [Pg.87]

Smog may result from a variety of environmental conditions when solar energy is responsible for the development of such conditions, it is referred to as photochemical smog. The production and destruction of photochemical smog are very complex events that involve hundreds of different chemical reactions. A full discussion of those reactions is beyond the scope of this book, but a general outline of the changes that take place is possible as follows. [Pg.43]

In the first step of photochemical smog production, sunlight (hv) acts on nitrogen dioxide to produce nitric oxide and free oxygen ... [Pg.43]

One product commonly formed in this reaction is peroxyacetyl nitrate (PAN), an important and common component of photochemical smog. PAN, ozone, and many of the other compounds formed in the series of reactions just described are strong oxidants and are responsible for some of the initial and most aggravating features of smog, including nose, eye, and throat irritation. [Pg.45]

Dodge, M. C., Formaldehyde Production in Photochemical Smog As Predicted by Three State-of-the-Science Chemical Oxidant Mechanisms, J. Geophys. Res., 95, 3635-3648 (1990). [Pg.934]

The solvent should not contain substances that contribute significantly to the production of photochemical smog and troposphere ozone. The volatile organic content of the product, as used, should not exceed 50 g/L. None of the components of the product will have a maximum incremental reactivity (MIR) exceeding 1.9 g Ofg of compound (the MIR for toluene). MIR values can be obtained from the maximum incremental reactivity list found in Appendix VII of the California Air Resources Board s California Exhaust Emission Standards and Test Procedures for 1988 and Subsequent Model Passenger Cars, Light-Duty Trucks and Medium-Duty Vehicles as amended on September 22, 1993. [Pg.95]

Photochemical air pollution is characterized by the formation of a so-called "photochemical oxidant" and the reduction of visibility due to the simultaneous production of aerosol particles or particulates. This type of air pollution is commonly known as "photochemical smog. ... [Pg.105]

Fig. VI-9. Concentration-lime history or reactants and some products in the photooxidation of C3H. Mixtures of C,H4 + NO + NOj in air were irradiated by simulated sunlight in smog chamber. Reprinted with permission from H. Niki, C. E. Daby, and B. Weinstock, in Photochemical Smog and Ozone Reactions, R. F. Gould, Ed., American Chemical Society, Washington, D. C. Copyright by the American Chemical Society, 1972. [Pg.201]


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See also in sourсe #XX -- [ Pg.96 ]




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