Urban atmosphere aromatic compounds

Sawicki, E., S. P. McPherson, T. W. Stanley, J. Meeker, and W. C. Elbert. Quantitative composition of the urban atmosphere in terms of polynuclear aza heterocyclic compounds and aliphatic and polynuclear aromatic hydrocarbons. Int. J. Air Water Pollut. 9 515-524, 1%5. 

One of the major uses of activated carbon is in the recovery of solvents from industrial process effluents. Dry cleaning, paints, adhesives, polymer manufacturing, and printing are some examples. Since, as a result of the highly volatile character of many solvents, they cannot be emitted directly into the atmosphere. Typical solvents recovered by active carbon are acetone, benzene, ethanol, ethyl ether, pentane, methylene chloride, tetrahydrofuran, toluene, xylene, chlorinated hydrocarbons, and other aromatic compounds [78], Besides, automotive emissions make a large contribution to urban and global air pollution. Some VOCs and other air contaminants are emitted by automobiles through the exhaust system and also by the fuel system, and activated carbons are used to control these emissions [77,78],... 

Benzene (see Fig. 2.4) is another pollutant component of automotive fuels. It occurs naturally in crude oil and is a useful component because it can prevent pre-ignition in unleaded petrol (the production process is usually adjusted so that the benzene concentration is about 5%). There is evidence that in some locations, where there has been a switch to fuels with high concentrations of aromatic hydrocarbons, there has been a sharp increase in photochemical smog. This is due to the high reactivity of these hydrocarbons in the urban atmosphere. This problem should draw our attention to the way in which the solution of one obvious environmental problem (lead from petrol) may introduce a second rather more subtle problem (i.e. increased photochemical smog from reactive aromatic compounds). 

The number of hydrocarbons in the atmosphere is potentially very large, since vapor pressures are favorable and the heavier species admit many isomers. In urban areas several hundred different hydrocarbons have been identified by gas chromatography (Appel et al, 1979 Louw el al, 1977). They include saturated compounds (alkanes) unsaturated species with one carbon-carbon double bond (alkenes) or two double bonds (alkadienes), acetylene type compounds (alkynes), and benzene derivatives or aromatic compounds (arenes). To separate that many different compounds requires... 

Alkenes and aromatic compounds have atmospheric lifetimes shorter than those of the low-weight alkanes. After 2 days of transport, propene and the butenes are reduced to a few percent of their original abundances relative to acetylene. If propene and the butenes are found at rural measurement sites, they must have local sources. Ethene, toluene, and ethylbenzene are less reactive. Their abundances relative to acetylene are reduced by a factor of about two after 2 days of transport. Toluene and ethylbenzene are primarily anthropogenic compounds. Both may serve as tracers for urban hydrocarbons in the same way as acetylene. In the cities the abundance... 

Aromatic compounds are of great interest in the chemistry of the urban atmosphere because of their abundance in motor vehicle emissions and because of their reactivity with respect to ozone and organic aerosol formation. The major atmospheric sink for aromatics is reaction with the hydroxyl radical. Whereas rate constants for the OH reaction with aromatics have been well characterized (Calvert et al. 2002), mechanisms of aromatic oxidation following the initial OH attack have been highly uncertain. Aromatic compounds of concern in urban atmospheric chemistry are given in Figure 6.16. 

Lee SC, Ho KF, Chan LY, Zielinska B, Chow CJ (2001) Polycyclic aromatic hydrocarbons (PAHs) and carbonyl compounds in urban atmosphere of Hong Kong. Atmos Environ 35 5949-5960... 

Volatile organic compounds include many products such as volatile hydrocarbons (alkanes, alkenes, aromatic compounds), carbonyl compounds (ketones, aldehydes), etc. In urban areas, they originate from motor vehicle exhaust gases, the evaporation of gasoline at filling stations, liquid fuels and industrial activities using solvents. Then-concentration may reach 50 ag-m in the atmosphere of large urban areas. 

The photodecomposition of the various oxidation products of the alkanes, alkenes, and the aromatic hydrocarbons play important roles in the chemistry of the urban, mral, and remote atmospheres. These processes provide radical and other reachve products that help drive the chemistry that leads to ozone generation and other important chemistty in the troposphere. In this chapter, we have reviewed the evidence for the nature of the primary processes that occur in the aldehydes, ketones, alkyl nitrites, nittoalkanes, alkyl nitrates, peroxyacyl nitrates, alkyl peroxides, and some representative, ttopospheric, sunlight-absorbing aromatic compounds. Where sufficient data exist, estimates have been made of the rate of the photolytic processes that occur in these molecules by calculation of the photolysis frequencies ory-values. These rate coefficients allow estimation of the photochemical lifetimes of the various compounds in the atmosphere as well as the rates at which various reactive products are formed through photolysis. 

Guidotti M, Giovinazzo R, Cedrone O, Vital M (1998) Investigation on the presence of aromatic hydrocarbons, persistent organochlorine compounds, phthalates and the breathable fraction of atmospheric particulate in the air of Rieti urban area. Ann Chim-Rome 88 419 27... 

Organic aerosols formed by gas-phase photochemical reactions of hydrocarbons, ozone, and nitrogen oxides have been identified in both urban and rural atmospheres (Grosjean, 1977). Most of these species are di- or poly-functionally substituted alkane derivatives. These compounds include aliphatic organic nitrates (Grosjean and Friendlander, 1975), di-carboxylic acids (adipic and glutaric acids) (O Brien et al., 1975), carboxylic acids derived from aromatic hydrocarbons (benzoic and phenylacetic acids), polysubstituted phenols, and nitroaromatics from aromatic hydrocarbons (Kawamuraet al., 1985 Satsumakayashi et al., 1989, 1990). Some species that have been identified in ambient aerosol and are be-... 

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