Atmosphere automobile exhaust

Formaldehyde is naturally produced in very small amounts in our bodies as a part of our normal, everyday metabolism and causes us no harm. It can also be found in the air that we breathe at home and at work, in the food we eat, and in some products that we put on our skin. A major source of formaldehyde that we breathe every day is found in smog in the lower atmosphere. Automobile exhaust... 

Typical examples of gaseous samples include automobile exhaust, emissions from industrial smokestacks, atmospheric gases, and compressed gases. Also included with gaseous samples are solid aerosol particulates. 

Air Pollution Control Device Meehanism or equipment that eleans emissions generated by a source (e.g., an incinerator, industrial smokestack or an automobile exhaust system) by removing pollutants that would otherwise be released to the atmosphere. 

Dibromoethane releases to the atmosphere historically have been due to fugitive emissions from leaded gasolines, automobile exhaust, and the former use of the compound as a fumigant (Fishbein 1979). 

In the early 1950 s, it was reported by Haagen-Smit that many of the characteristics of photochemical smog could be explained by the presence of ozone and other photochemical oxidants. These substances, he believed, were formed in the atmosphere as a result of chemical reactions involving nitrogen oxides and hydrocarbons present in automobile exhaust. Significant quantities of nitrogen oxides were also emitted by power plants. 

Considerable time elapsed before there was general acceptance of Haagen-Smit s important discovery, in part because of its subtle nature. For the first time, a major air pollution problem was demonstrated to be caused by a pollutant generated in the atmosphere. Its effect often did not become apparent until many miles downwind from the source. (The same suspicion has been attached to sulfate-containing aerosols for many years, but the proof that the sulfate is damaging is not as well established.) In addition, a new pollution source, automobile exhaust, had been shown to be of prime importance. 

More than 100 compounds are released in the atmosphere of urban areas by automobiles, and there is a close relation between the atmospheric hydrocarbon composition and the composition of gasolines and automobile exhausts. The full range of compositions of gasolines has been reported by Sanders and Maynard.They identified 180 of the 240 compounds separated by capillary-column gas chromatography. Detailed fiiel compositions were reported by other investigators, and exhaust hydrocarbon compositions were reported by Neligan et a/.,McEwen, and, more recently. Papa et Jacobs, ... 

The observed ambient organic aerosol formation rates are also consistent with those estimated by extrapolation of smog-chamber kinetic data. Other heavy unsaturates, such as styrene and indene, are present in the atmosphere and may contribute, in part, to the formation of benzoic acid and homophthalic acid, respectively. Diesel exhaust and industrial emission are possible sources of such heavy unsaturates. Diolefins of C6+ are not present in gasolines and exhaust gases and have not been found in the atmosphere, and their possible role as precursors of the Cs-7 difiinctional acidic compounds is seriously challenged. Lower diolefins are emitted in automobile exhaust. Examination of vapor-pressure data indicates that the bulk of their expected photooxidation products remains in the gas phase, including most of the less volatile C3-4 dicarboxylic acids. 

Cresols have been identified as components of automobile exhaust (Hampton et al. 1982 Johnson et al. 1989 Seizinger and Dimitriades 1972), and may volatilize from gasoline and diesel fuels used to power motor vehicles. Vehicular traffic in urban and suburban settings provides a constant source of cresols to the atmosphere. Hence, urban and suburban populations may be constantly exposed to atmospheric cresols. Cresols are also emitted to ambient air during the combustion of coal (Junk and Ford 1980), wood (Hawthorne et al. 1988, 1989), municipal solid waste (James et al. 1984 Junk and Ford 1980), and cigarettes (Arrendale et al. 1982 Novotny et al. 1982). Therefore, residents near coal- and petroleum-fueled electricity- generating facilities, municipal solid waste incinerators, and industries with conventional furnace operations or large-scale incinerators may be exposed to cresols in air. People in residential areas where homes are heated with coal, oil, or wood may also be exposed to cresols in air. 

This is an extremely important reaction to which we wiU refer throughout this book. It is responsible for all NO, formation in the atmosphere (the brown color of the air over large cities) as well as nitric acid and acid rain. This reaction only occurs in high-temperature combustion processes and in lightning bolts, and it occurs in automobile engines by free-radical chain reaction steps, which will be the subject of Chapter 10. It is removed from the automobile exhaust in the automotive catalytic converter, which wiU be considered in Chapter 7. 

One interesting potential source of N20 is the heterogeneous oxidation of HONO on surfaces (Wiesen et al., 1995 Pires and Rossi, 1997), which has been observed to form N20. This is likely responsible for the observation of significant amounts of N20 in automobile exhaust, which was shown to be an artifact of sampling (Munzio and Kramlich, 1988). However, it may also occur on aerosol particles in the atmosphere (Clemens et al., 1997), an area that warrants further investigation. 

The following, well-acceptable assumptions are applied in the presented models of automobile exhaust gas converters Ideal gas behavior and constant pressure are considered (system open to ambient atmosphere, very low pressure drop). Relatively low concentration of key reactants enables to approximate diffusion processes by the Fick s law and to assume negligible change in the number of moles caused by the reactions. Axial dispersion and heat conduction effects in the flowing gas can be neglected due to short residence times ( 0.1 s). The description of heat and mass transfer between bulk of flowing gas and catalytic washcoat is approximated by distributed transfer coefficients, calculated from suitable correlations (cf. Section III.C). All physical properties of gas (cp, p, p, X, Z>k) and solid phase heat capacity are evaluated in dependence on temperature. Effective heat conductivity, density and heat capacity are used for the entire solid phase, which consists of catalytic washcoat layer and monolith substrate (wall). 

Tremp, J., P. Mattrel, S. Fingler, and W. Giger, Phenols and nitrophenols as tropospheric pollutants Emissions from automobile exhausts and phase transfer in the atmosphere , Water Air Soil Pollut., 68,113-123 (1993). 

A number of complex chemical compounds (e.g., pesticides, vapors and fumes, automobile exhausts, petroleum distillates, foundry fumes, heterocyclic amines, solid particles) have caused adverse effects to humans and environment. Some persistent contaminants have originated from industrial sources. For example, DDT, mirex, PCBs, dioxin, and others have been traced in the atmosphere as toxic depositions causing concern to human health.3... 

Ffowever, such DNA ligands are often toxic or carcinogenic. Nowadays it is well known that several pollutants exhibit carcinogenicity through intercalation into DNA. Some examples are PAFfs or aromatic amines, and some endocrine disruptors, in coal tar, atmospheric pollutants, automobile exhaust, and cigarette smoke. PCDDs, PCDFs, and PCBs have especially emerged as... 

In our industrialized society, pollutants are being released into our atmosphere in the form of gases and chemical compounds adsorbed onto tiny particles. For example, one such class of compounds which is of concern is polynuclear aromatic hydrocarbons (PAH) since some of these compounds are reported to be carcinogenic. Three PAHs which can be formed during incomplete combustion have been identified in steel coking operations, automobile exhaust, and cigarette smoke. 

Nitrogen dioxide is a reddish-brown gas that is heavier than air. It typically exists in the atmosphere as an equilibrium mixture with nitrogen tetroxide. As a relatively stable free radical, it can be found in ambient air at high concentrations near a source such as automobile exhaust or an electric arc. High concentrations are also found in grain silos. The chemical and physical properties of nitrogen dioxide are summarized in Table 8-1. 

The involvement of N02 and NO (NO ) is of great importance in atmospheric pollution, arising mainly from automobile exhausts, but this topic will not be dealt with here. 

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