Atmospheric emissions Benzene

Figure 7. Schematic diagram of by-product coke oven showing possible atmospheric emission sources for Benzene. (Reproduced with permission from Ref. 3.)...

Table I illustrates the estimation of ambient exposures to benzene associated with various categories of atmospheric emission sources. Since benzene is a suspected carcinogen, annual exposure is an appropriate measure for assessing long-term effects.

For solvent operations, benzene use had to be estimated by a series of tenuous assumptions about the amount of benzene in "other uses," the percent of that used for solvents, and the loss of benzene from those operations. As an upper limit, it might be assumed that all of the purchased benzene is eventually lost to the atmosphere. However, some measured concentrations suggest that perhaps only 10% is lost at the plant. The remainder might be incinerated after becoming unusable or sent elsewhere for disposal. A general rule for volatile solvents is that they eventually reach the environment unless they are destroyed deliberately or degrade naturally. The distribution of solvent emissions geographically is much more difficult to determine. 

PEDCo Environmental "Atmospheric Benzene Emissions," PEDCo Environmental, Inc., 1977. 

The development of new models for the prediction of chemical effects in the environment has improved. An Eulerian photochemical air quality model for the prediction of the atmospheric transport and chemical reactions of gas-phase toxic organic air pollutants has been published. The organic compounds were drawn from a list of 189 species selected for control as hazardous air pollutants in the Clean Air Act Amendments of 1990. The species considered include benzene, various alkylbenzenes, phenol, cresols, 1,3-butadiene, acrolein, formaldehyde, acetaldehyde, and perchloroethyl-ene, among others. The finding that photochemical production can be a major contributor to the total concentrations of some toxic organic species implies that control programs for those species must consider more than just direct emissions (Harley and Cass, 1994). This further corroborates the present weakness in many atmospheric models. 

In the meantime, the reactivity of milled aluminum correlated well with the intensity of exoelectron emission. Such an emission decayed with time after termination of milling, along with the suppression of the chemical reaction. The aluminum, which had entirely lost electron emission activity, did not react with butyl bromide at all. Alkyl halides capture free electrons. The emission intensity of the free (unused) electrons under butyl bromide atmosphere was less than 20% of that under benzene atmosphere. In other words, exoelectrons are captured with butyl bromide more easily than with benzene. Butyl bromide has much stronger electron affinity than benzene. 

Chiba et al. [749] used atmospheric pressure helium microwave induced plasma emission spectrometry with the cold vapour generation technique combined with gas chromatography for the determination of methylmercuiy chloride, ethylmercury chloride and dimethylmercury in sea water following a 500-fold preconcentration using a benzene- cysteine extraction technique. 

The environmental effects from the emission of these chlorinated benzenes are estimated to be insigificant because of the low levels and the further dilution by factors of 103 to 105 in the atmosphere before any hunan or plant exposure. 

Use of RFC decreases the amounts of volatile organic compounds (VOCs) and oxides of nitrogen (NO ) in the atmosphere that react in the presence of sunlight to produce ozone, a major component of smog. Vehicles also release toxic emissions, one of which (benzene) is a known carcinogen. 

Solvents are widely used in the chemical industry and play a variety of roles e.g. mass and heat transfer (Adams et al, 2004). They are conventionally volatile organic compounds (VOC) that lead to significant emissions to the atmosphere and possess substantial risks such as flammability and toxicity. Some of these solvents are already banned in the pharmaceutical industry (e.g. benzene) and others... 

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],... 

Guerra G, Lemma A, Lerda D, et al. 1995. Benzene emissions from motor vehicle traffic in the urban area of Milan hypothesis of health impact assessment. Atmospheric Environment 29(23) 3559-3569. 

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). 

As a fourth step, discussion continues for the introduction of emission limits for other exhaust gas components, and for particulate matter of diesel powered vehicles. For example, there has been discussion in the USA and some European countries on separate - additional - emission limits for carbon dioxide, benzene and/or aldehydes. In the USA there is a project to consider an additional ozone-formation factor to be allocated to the tailpipe emission of passenger cars. This is because each exhaust gas component has a different potential to contribute to atmospheric ozone formation. This potential is quantified according to the theory of Carter by the maximum incremental reactivity (MIR) factor, expressed as grams of... 

Fossil-fueled vehicles give rise to emissions of unburned fuel and partially oxidized hydrocarbons [102,106]. Prominent are the BTEX suite of aromatics - benzene, toluene, ethylbenzene, and xylenes. These compounds are ubiquitous in the environment, present in essentially every hive atmosphere we test and often among the most prominent peaks in the chromatogram. To date, it has not been possible to position a bee colony that avoids capture of significant amounts of BTEX. We also detect more biorefractive fuel components in hive air - polycyclic aromatics and biphenyls commonly associated with diesel products [114]. Incompletely burned fuel residuals [102] were also evident as noted in the Oxygenates portion of Table 2.5. These comprised aldehydes, ketones, alcohols, and oxides. 

Real primary emissions consist of a complex mixture including Unear and branched alkanes, mono aromatics, substituted aromatics (alkyl benzenes), and PAHs, among many other compounds [7, 142]. The most direct evidence that SOA formation is important for typical atmospheric IVOC mixtures thus comes from experiments on vapors from these very mixtures [127, 143-148]. 

Aromatic VOCs are released into the atmosphere from a wide range of sources. It is surprising that these emissions still originate partly from gasoline-fuelled vehicles. This is because benzene and other aromatics remain in gasoUne due to their high octane number. Emissions from stationary sources are also abundant and come from a variety of industries, such as chemicals, petrochemicals, paints, coatings... 

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