Alkyl PAHs

Finally, since our focus is on the atmospheric chemistry of unsubstituted (or methyl substituted) PAHs, we do not discuss major classes of PAHs from natural sources that are not found at significant levels in ambient air but may be important in soil and water environments, e.g., alkylated PAHs (see the review by Si-moneit, 1998). 

The rank of coal (maturity) is an important factor that affects PAH emissions from residential combustion. PAH emission from various coals is found to have a relationship with their volatile contents, and the complete combustion of coals with a high volatile content is more difficult to achieve. Bituminous and sub-bituminous coals with high volatile content yield more PAHs when burned at low temperatures, such as residential combustion, while anthracite coal containing very little volatile matter can burn more completely and emit PAHs with a mass that is three orders of magnitude lower than bituminous coal. Smoky coal, which is burned as fuel for cooking and heating in unvented homes, produces combustion emissions composed primarily of parent PAHs and alkylated PAHs. 

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.

Two other samples have PAH distributions that do not correspond to the pattern seen in the other sediments and soils. They are the Alaska K-30 sediment and the Enewetok soil. Both have patterns with relatively high abundances of alkylated PAH (see Figure 3). The sample site description for the Alaskan sediment indicates that the sample was taken near an oil seep. It is not surprising that the PAH pattern should reflect the high degree of alkylation found in petroleum (1,22). Figure 3 graphically demonstrates this pattern for a crude oil as well as for a shale... 

Petroleum and low-temperature combustion processes yield primarily highly alkylated PAHs, while high-temperature combustion sources result in many nonalkylated PAHs. If this is generally the case, we must conclude, from an examination of the data in Figures 5-11, that the PAHs in these samples generally have dual sources or that they have undergone substantial biochemical and/or physical modifications. If petroleum is a... 

OPAHs, NPAHs, and alkylated PAH derivatives, as well as other unidentified structural isomers of PAHs. 

SPME with PDMS fibers was employed to measure PAHs and alkylated-PAHs in groundwater samples collected over two years from sites contaminated with coal tar and refinery wastes.NAP was the predominant PAH detected. Heavier PAH concentrations were much lower due to partitioning onto soils and sediments. Source determination by examining isomer ratios was difficult due to the very low concentrations measured. Very low detection limits were achieved, 0.07 ng ml . ... 

Online LC-GC-ITD-MS was used to identify alkyl-PAH, OP AH, and NPAH in supercritical fluid extracts of particulate matter on quartz filters, collected in DCM, and solvent exchanged into... 

Aromatic hydrocarbons are cyclic, planar compounds that are stabilized by a delocalized tt electron system. Aromatics include the mono aromatic hydrocarbons such as BTEX (benzene, toluene, ethylbenzene, and o-, m-, and p-xylenes) and other alkyl-substituted benzene compounds (C -benzenes), and polycyclic aromatic hydrocarbons (including oil-characteristic alkylated PAH homologues and the other U.S. EPA priority PAHs). Benzene is the simplest one ring aromatic compound. The commonly analyzed PAH compounds range from two ring PAHs (such as naphthalene) up through six ring PAHs (benzo g, h, i) perylene). BTEX and PAHs are of concern because of their toxic properties in the environment. 

Do not measure dominated alkylated PAH homologues, aliphatics and biomarkers in oils Provide little diagnostic source information... 

In recent several years, many EPA and ASTM methods have been modified (such as the modified EPA method 8015, 8260 and 8270 and the modified ASTM methods 3328-90, 5037-90 and 5739-95) to improve specificity and sensitivity for measuring spilled oil and petroleum products in soils and waters by environmental chemists. For example, EPA Method 8270 has been modified to increase analytical sensitivity and to expand the analyte list to include petroleum specific compounds such as the alkylated PAHs, sulfur, and nitrogen containing PAHs, and biomarker triterpane and sterane compounds. The principal modification to EPA Method 8270 is the use of the high resolution GC-MS selected ion mode (SIM) analysis that olfers increased sensitivity relative to the full scan mode. Many environmental laboratories have used the modified EPA Method 8270, combined with column cleanup and rigorous QA measures, to identify and quantify low levels of hydrocarbons. 

The EPA priority parent PAHs and, in particular, the petroleum specihc alkylated (Ci to C4) homologues of selected PAHs (that is, alkylated naphthalene, phenanthrene, dibenzothiophene, fluorene, and chrysene series). These alkylated PAH homologues (Table 27.4) are the backbone of chemical characterization and identification of oil spill assessments ... 

Oil-characteristic alkylated PAHs Other EPA priority PAH pollutants ... 

In this tiered analytical approach, the high resolution capillary GC-FID analysis is applied to evaluate hydrocarbon groups (including TPH, UCM, the total saturates and total aromatics), to determine concentrations of n-alkanes and major isoprenoid compounds, and to characterize the product types in fresh to highly weathered oil samples. The GC -MS analysis provides data on the source specific marker compounds including the target alkylated PAH homologues and other... 

A microcolumn packed with 3 g of activated silica gel is used for sample cleanup and fractionation. An aliquot of the extract (containing about 20 mg oil or TSEM) is then transferred to the silica gel cleanup column to remove polar components and other interferences. The column is eluted first with hexane, which recovers samrated hydrocarbons as Fraction 1 (FI). The mixture of hexane/DCM or hexane/benzene (1 1, v v) is used to elute the aromatic compounds as Fraction 2 (F2). Half of FI and half of F2 are combined into the Fraction 3 (F3). These three fractions are concentrated to appropriate volume (0.5 to 1.0 ml) by nitrogen purge. The quantitation internal standards are 5-a-androstane, di4-terphyl, and C30 17(3(H), 21(3(H)-hopane. The Fraction 3 is analyzed for quantitation of the TPH and the UCM by GC-FID. The Fraction 1 is analyzed for determination of n-alkanes by GC-FID and biomarker terpanes and steranes by GC-MS. The Fraction 2 is analyzed for the determination of alkylated PAH homologues and other EPA priority unsubstantiated PAHs by GC-MS. 

The GC-MS analysis is conducted by injection of 1 /xL of FI orF2 into a gas chromatograph-mass spectrometer. The MS detector is operated in the scan mode to obtain spectral data for identification of components and in the selected ion mode (SIM) for quantitation of target compounds. An appropriate temperature program is selected to achieve near-baseline separation of all of the target components. Quantitation of the alkalized PAH homologues, other EPA priority PAHs and biomarker compounds are performed by the internal standard method with the RRFs for each compound determined during the instrument calibration. The ions monitored for alkylated PAH and biomarker analyses are listed in Table 27.4 and Table 27.5, respectively. 

Quantifying the alkylated PAH homologues using RRFs obtained directly from authentic alkylated PAH standards, rather than the standard parent PAH compounds... 

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