Benzene exhaust emissions

A preliminary investigation carried out by the Public Health Engineering Laboratory of Imperial College utilized three fuels of similar RON and benzene content (Table II). Benzene exhaust emissions were monitored using varying aromatic contents in the input fuels balanced with differing lead alkyl additions to maintain the same octane requirements. 

Seven exhaust emission equations for VOCs and NO, and five for toxins (benzene, butadiene, formaldehyde, acetaldehyde, and polycyclic organic material (POM). 

Four corresponding non-exhaust emission equations for benzene. 

Inherently low exhaust emission levels of nonmethane hydrocarbons and air pollutants such as benzene... 

Owing to their greater exposure to motor vehicle exhaust emissions, it is possible that fatty foods on sale at shops attached to petrol stations or at stalls and shops in busy roads could contain higher concentrations of aromatic hydrocarbons than similar foods on sale at other shops. A study in Germany found that concentrations of benzene and toluene were higher in retail packs from petrol stations on busy roads than from petrol stations in rural areas.15 It also found that retail packs from shops in busy roads contained higher concentrations of benzene, toluene, xylenes and ethylbenzene than retail packs from shops in residential areas. 

Production of benzene could be important in terms of pollution from exhaust emissions in gasoline engines. In the cyclohexane chemistry above, increased ring homolysis above 750 K might well be expected with the formation of C2H4 and butadiene through the sequence... 

Regulations limiting the concentration of benzene and the total aromatic content of finished gasoline have been established for 1995 and beyond in order to reduce the ozone reactivity and toxicity of automotive evaporative and exhaust emissions. Test methods to determine benzene and the aromatic content of gasoline are necessary to assess product quality and to meet new fuel regulations. 

Workplace exposure limits for benzene have been regulated to levels as low as 0.5 ppm (43). Industrial emissions affecting the pubHc ate now low enough that the EPA considers that a greater hazard exists from mosdy indoor sources such as smoking, automobile exhausts, and consumer products (44). 

Exhaust benzene is a function of aromatics and benzene content. Exhaust benzene emission is calculated by ... 

Unbumt gasoline and cracked hydrocarbons such as ethylene and propylene are also substantial constituents of exhaust. Gasoline contains additives such as benzene, toluene and branched hydrocarbons to achieve the necessary octane numbers. The direct emission of these volatile compounds, e.g. at gas stations, is a significant source of air pollution. Leaded fuels, containing antiknock additions such as tetra-ethyl-lead, have been abandoned because lead poisons both human beings and the three-way exhaust catalyst, especially for the removal of NO by rhodium. 

Aromatics are typically included in gasolines to increase octane number. However, high aromatic content increases engine-out hydrocarbons and NOx emissions.16 Moreover, aromatics are the main precursors of exhaust benzene, a known carcinogenic, via dealkylation of substituted aromatics.17 Therefore, reduction of total aromatic content, together with olefin content, is an important part of California phase III reformulated gasoline specifications,18 with respect to the current allowed concentrations of benzene and total aromatics of 0.8 and 25 percent of volume, respectively. 

Hexane may be expected to comprise around 2% of the VOCs in urban air polluted with hydrocarbons from automobile emissions or other combustion byproducts (Barrefors and Petersson 1993). The -hexane concentrations in urban air will typically be approximately 60% of the concentrations of benzene (Daisey et al. 1994). Close proximity to the exhaust systems of cars or other gasoline-powered vehicles can lead to exposures to increased concentrations of -hexane. Under rush-hour conditions, the concentrations in the interior air of buses will tend to be lower (55 g/m3 or 19.8 ppbv) than the interior levels in cars (69 g/m3 or 24.9 ppbv) or the air around persons riding motorcycles (106 g/m3 or... 

Source Detected in distilled water-soluble fractions of 87 octane gasoline (24.0 mg/L), 94 octane gasoline (80.7 mg/L), Gasohol (32.3 mg/L), No. 2 fuel oil (0.50 mg/L), jet fuel A (0.23 mg/L), diesel fuel (0.28 mg/L), militaryjet fuel JP-4 (17.6 mg/L) (Potter, 1996), new motor oil (0.37-0.40 jg/L), and used motor oil (195-198 Jg/L) (Chen et ah, 1994). Diesel fuel obtained from a service station in Schlieren, Switzerland contained benzene at a concentration of 76 mg/L (Schluep et al, 2001). The average volume percent and estimated mole fraction in American Petroleum Institute PS-6 gasoline were 2.082 and 0.2969, respectively (Poulsen et al, 1992). Schauer et al. (1999) reported benzene in a diesel-powered medium-duty truck exhaust at an emission rate of 2,740 pg/km. 

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],... 

All outdoor sources, including automobile exhaust and stationary source emissions, account for only about 20% of the total population exposure to benzene (Wallace 1989b). The main outdoor source is likely to be automobile exhaust (Wallace 1995). Average air intake of benzene for urban/suburban residents (assuming atypical concentration range of 2.8-20 ppb and an intake of 20 m3 air/day) is 180-1,300 pg/day. 

In addition to particulate emissions, volatile organic compounds (VOCs) may also be emitted when the slurry contains organic materials with low vapor pressures. The surfactants included in the slurry represent the origin of the VOCs. The vaporized organic materials condense in the tower exhaust air stream into droplets or particles. Paraffin alcohols and amides in the exhaust stream can result in highly visible plume that persists after the condensed water vapor plume has dissipated [4, 21]. Some of the VOCs identified in the organic emissions are hexane, methyl alcohol, 1,1,1-trichloroethane, perchloroethylene, benzene, and toluene [1-4]. 

A method for determining kp reported by Cundall and Pereira (91) utilizes data from the parallel studies on parameters controlling the spin-allowed emission. In these studies, most exhaustively pursued for benzene, it Is found that both kp and kisc approach limiting low-temperature values, and estimates of their magnitude In the < 100°K region may be given with some certainty. With this information, the additional data for Xp and for 0p/0p (x) hp can be determined, since... 

Automobile exhaust is another source of 2,4- and 2,6-DNPs in air (Nojima et al. 1983). 2,4-DNP is also used as an insecticide, acaricide, and fungicide (HSDB 1994). Therefore, application of this type of pesticide could be a source of 2,4-DNP in air. Photochemical reactions of benzene with nitrogen oxides in air also produce dinitrophenols in the atmosphere (Nojima et al. 1983). Dinitrophenols have been detected in emissions from hazardous waste combustion (James et al. 1984). Dinitrophenols may be present in the aerosol or vapor phase near hazardous waste disposal sites. It has been suggested that the most important origin of dinitrophenols is their formation by photochemical reactions in the atmosphere (Nojima et al. 1983). 

Complex Model. A complex model is a set of statistically derived equations that relate fuel properties to vehicle emissions. This model became mandatory in 1998. The simple model calculates emission based on a fuel s RVP, oxygen, aromatic, and benzene content whereas the complex model adds four more variables (sulfur, olefin, and the 200 F and 300°F distillation volume fractions) to the equation. This model is based on the data collected from programs conducted around the United States. The database was made up of over 200 test fuels, 500 automobiles, and 5000 emission test-ings. The complex model can be divided into two portions exhaust and nonexhaust. The nonexhaust VOC was derived directly from the simple model approach where the nonexhaust benzene was modeled as a weight fraction of nonexhaust VOC from the headspace model of General Motors. The exhaust model was based on 19 different test programs. ... 

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