Source petrogenic

The mixture of PAHs present in a particular sample in many cases mirrors the sources that produce them. Several methods can be used to qualitatively identify the probable sources of PAHs. Commonly used methods include the abundance ratios of individual compounds, the fossil fuel pollution index (FFPI), and diagnostic ratios indicative of sources (petrogenic vs. pyrogenic). Quantitative apportionment of sources needs sophisticated statistical approaches such as the chemical mass balance models (Li et al., 2003). 

PAHs are released to the environment from a number of sources pyrogenic sources including fossil fuel combustion and pyrolytic processes of organic matter such as incineration and petrogenic sources such as oils spills. Direct oil spilled from stationary sources and accidents cause contamination of land. Oil spills at US Army bases in South Korea is reported as a source of soil and groundwater contamination to nearby area... 

Therefore, Ph/An> 15 may point to petrogenic sources and Ph/An< 10 to pyrolytic sources. Due to the wide range of values for this index found in the literature, values between 10 and 15 are considered indeterminate relative to source. In petroleum-derived PAHs, pyrene is more abundant than fluoranthene, while at higher combustion temperatures a predominance of fluoranthene over pyrene is characteristic. So the Fl/Pyr values greater than 1 are obviously related to pyrolytic sources, whereas values less than 1 are attributed to petrogenic sources. In order to avoid erroneous conclusions, the two ratios are often combined. When Ph/An> 15 and Fl/Pyr < 1, the PAH input is mainly from crude oil sources and when Ph/An< 10 and Fl/Pyr > 1, the major input may be related to combustion (Wang et ah, 2004b). 

Sources of PAHs can be distinguished by using select ratios. For example, ratios of total methylphenanthrenes to phenanthrene is used to identify PAHs as pyrolytic or petrogenic sources. Other work has resorted to the application of compound-specific isotope analysis (CSIA), to constrain better anthropogenic sources of PAHs. 

PAFIs and their alkylated derivatives are also used to distinguish between pyrolytic and petrogenic inputs to sediments and soils and are often used in conjunction with aliphatic indices to discriminate hydrocarbon sources. The lower molecular weight 2- to 4-ringed PAHs and their alkylated versions comprise a small, but significant, component of crude oils and liquid fuels. Ratios of parent PAHs (non-alkylated) as well as parent to alkylated versions are frequently used to distinguish... 

PAHs to distinguish them from the petrogenic PAHs derived directly from uncombusted petroleum, coal, and their by-products. Natural sources such as forest fires could be important in less inhabited and remote watersheds, but anthropogenic combustion of fossil fuel (e.g., petroleum, coal) and wood is the dominant source of pyrogenic PAHs (Neff, 1979 Bjorseth and Ramdahl, 1983 Ballentine et al., 1996 O Malley et ai, 1997). 

Figure 5 PAHs distribution in petrogenic sources. Compound symbols as in Figure 2 with the modifier M (methylated), D (dimethylated), and T (trimethylated) added for alkylated PAH.

The reactivity of MPa and BaP seems to have resulted in the alteration of their source compositional ratios during transportation/deposition, and thus may not be a reliable source indicator. In addition to the compositional attributes of the parental PAHs, the presence of methylated compounds and a UCM in the surface sediments indicates possible petrogenic inputs of PAHs to the Harbor. The UCM is generally indicative of petroleum and petroleum products, and is a widely used indicator of petrogenic contamination in sediments (Prahl and Carpenter, 1979 Volkman et al., 1992, 1997 Simoneit, 1998). It is commonly assumed that a UCM consists primarily of an accumulation of multibranched structures that are formed as a result of biodegradation reactions of petroleum (Volkman et al., 1992). Since no clear indication of petroleum-derived inputs can be discerned from the compositional ratios of the prominent PAHs in the sediments, it is apparent that the isomeric ratios of the prominent petrogenic PAHs are masked by pyrogenic-derived components. 

Examination and comparison of these ratio plots and dot maps for each of the two fields indicate that the more anomalous magnitude sites (large dots) match the composition of the known underlying reservoirs. The areal groupings and Pixler ratio plots of these specific components with their appropriate reservoirs lends confidence to the deduction that these soil-gas anomalies are the result of migration of petrogenic hydrocarbons from the underlying sedimentary sources. 

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