Automobile exhausts, volatile aromatics

Table I presents the relative values for the maximum rate of nitrogen dioxide formation, Table II gives the maximum rates for hydrocarbon disappearance, and Table III presents the relative oxidant maxima. For comparison, we have included the values for a,a,a-trifluorotoluene, a particularly unreactive aromatic hydrocarbon propylene, one of the principal hydrocarbons in automobile exhaust (13) and 2-methyl-2-butene, an especially volatile and reactive olefin that is often present in small amounts in gasoline (12).

Benzene, toluene, and their derivatives enter the atmosphere by various mechanisms such as controlled emissions from consumer industries, volatilization from waste dumps and landfill sites, intentional spraying and dusting, and from automobile exhaust. Since such compounds are moderately soluble in water, they are probably washed out of the atmosphere with rainfall, deposited in surface waters, and then evaporated back into the atmosphere. Although this recycling process may be a significant source of aromatic... 

Every year, about 50 million t hydrocarbons are discharged into the atmosphere from refineries and automobile exhausts, about 20 million t from incineration plants, and about 20 million t from other man-made sources [10, 11], of which only part is aromatic. These emissions could contain some 10-20 million t volatile aromatics [12]. Another estimate is based on world emissions of hydrocarbons from stationary plants of 54 million t (USA 7-18 million t) and from mobile sources (transportation means) of 34 million t (USA 12-20 million t) [13]. It has also been calculated that world evaporation losses of hydrocarbons from the production and processing of petroleum amount to 44.7-68 million t (approx, one-quarter of this in refineries), and emissions from the combustion of by-products in the oil processing industry to 28 million t [5]. In these figures, too, the volatile aromatics naturally account for only a portion, perhaps one-fifth. 

While in general a fair amount is known about the transport of petroleum fractions and hydrocarbons, the specific behaviour of volatile aromatics has not been studied to any great extent. It is known that they are carried through the air over relatively long distances. For example, aromatic fractions from automobile exhaust gases in the Zurich area are found in Lake Zurich and the river Glatt [64,65]. Similarly, ethyl benzene, xylenes, n-propyl benzene, ethyl toluenes and trimethyl toluenes from Sydney have been detected in remote regions of New South Wales [66]. 

Only insufficient information is available concerning the exchange of volatile aromatics between the atmosphere and water. It can be reliably assumed that rainfall precipitates volatile aromatics from the atmosphere, whereupon they are introduced directly or indirectly into surface water. The occurrence of aromatic fractions from automobile exhaust gases in Lake Zurich and the river Glatt, mentioned above, provides evidence that such an exchange actually does take place [64, 65] for other water ways see [67,68] and a later section [see also 291, 292]. 

The extremely high values in Sheffield and London are due to the fact that measurements were taken in narrow streets on a level with automobile exhausts. In the case of the industrial sites, air samples were taken at a distance of approximately 100 m from the factory. Considering the vertical distribution, the maximum toluene and xylene concentrations are found at a height of 140 m, but here temperature inversion situations also play a role [150]. Environmental research into pollution by volatile aromatics as a result of vehicular traffic is being conducted in numerous locations (see, for example [13, 142, 151-155]). Other groups are engaged in examining the transport of pollutants [66] into unpolluted areas and any... 

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],... 

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