Polycyclic aromatic hydrocarbons (PAH),t also known as polynuclear aromatic hydrocarbons or polyarenes, constitute a large class of organic compounds. They are formed and released into the environment through natural and man-made sources. Natural sources include volcanoes and forest fire, while the man-made sources come from wood burning, automobile exhaust, industrial power generators, incinerators, production of coal tar, coke, asphalt and petroleum, incomplete combustion of coal, oil, gas, garbage, tobacco and charbroiled meat. Polycyclic aromatic heterocyclic analogs containing one or more nitrogen, oxygen or sulfur atoms are also present in substantial quantities in coal tar and petroleum residues produced during the refining process. In the atmosphere, they are principally generated from the combustion of fossil fuels, wood or forest burning, refuse burning and coal tar. Although anthropogenic sources account for the major portion of atmospheric PAH pollution (l), vehicle emissions are believed to be responsible for 35% of the total PAH emission in highly populated and industrialized urban areas of the United States (2). Deposition of PAH in surface and ground waters can take place from a variety of sources such as airborne PAH, municipal wastewater discharge, effluents from wood treatment plants and other industries, oil spills and petroleum pressing. Accumulation of PAH in soils is believed to result from atmospheric deposition after long-range transport. The concentration of PAH found in soil around urban and industrialized areas are sometimes up to two orders of magnitude higher than those in less-developed areas (derived from forest fires and airborne pollution). Once released into the environment, PAH can partition between air, water, soil or sediments. An extensive body of work on this subject has appeared in the literature in recent years. Representative examples include partitioning of PAH between the gas and suspended particle phase (3,4), aidwater

A Compilation of Physical, Spectroscopic and Photophysical Properties of Polycyclic Aromatic Hydrocarbons

Relative rate constants for the heterogeneous reactions of OH, NO2 and NO radicals with polycyclic aromatic hydrocarbons adsorbed on carbonaceous particles. Part 1: PAHs adsorbed on 1–2 μm calibrated graphite particles

The relative spacing of amines in 3-aminopropylsilyl-grafted silica is studied by solid-state fluorescence spectroscopy of 1-pyrenecarboxylic acid (PCA) and 1-pyrenebutyric acid (PBA) bound to traditionally prepared, deprotected benzyl- or deprotected trityl-spaced aminosilicas. Thermogravimetric analysis and FT-Raman spectroscopy results show evidence that the protected imine can be cleaved to yield the corresponding amine in essentially quantitative yield. The steady-state fluorescence spectroscopic data of either PCA or PBA indicate that the number of amine pairs on the surface separated by a distance of 1 nm or less decreases as the total amine loading decreases. Both the intensity ratio of the excimer band to the monomer band (I470/I384 or Iexc/Imon) and lifetime decay studies of the fluorophore are useful probes of the amine spacing. Separation of amines on the surface can be achieved by either use of a protected synthesis route or through reduction of the concentration of the unprotected 3-aminopro...

Spacing and Site Isolation of Amine Groups in 3-Aminopropyl-Grafted Silica Materials: The Role of Protecting Groups

Disappearance of polycyclic aromatic hydrocarbons sorbed on surfaces of pine [Pinua thunbergii] needles under irradiation of sunlight: Volatilization and photolysis

Photocatalytic degradation of phenanthrene and pyrene on soil surfaces in the presence of nanometer rutile TiO2 under UV-irradiation

The emission spectroscopy of fluorene has been studied at a silica gel/air interface at surface loadings from 1.5% to 77.1% of a monolayer. Both monomer and excimer-like emissions are observed on the surface. The excimer-like emission, centered at 350 nm, arises from excitation of ground-state van der Waals pairs of fluorene molecules. Photolysis into the van der Waals dimers at room temperature does not lead to dissociation into constituent monomers; however, irradiation of fluorene monomers at a silica gel/air interface leads to production of 9-fluorenone as the only identifiable photoproduct in 72% yield. Fluorene triplet and cation radical are both observed at the silica gel/air interface by transient diffuse reflectance spectroscopy. Sensitization of singlet molecular oxygen by silica-sorbed methylene blue, in the presence of co-sorbed fluorene, does not lead to fluorene oxidation, thus suggesting that oxidation by direct photolysis does not involve an energy transfer mechanism. An electron transfer oxidation mechanism is proposed to account for the observed photochemical oxidation of fluorene at the silica gel/air interface.

Spectroscopy and photochemistry of fluorene at a silica gel/air interface

The photolysis of acenapthene (ACE) has been studied at a silica gel/air interface. Direct photolysis leads to 1-acenaphthenol as the principal photoproduct. Secondary photochemical conversion of the alcohol into 1-acenaphthenone is also observed. Reactions leading to formation of both 1-acenaphthenol and 1-acenaphthenone are attributed to electron-transfer oxidation mechanisms and the cation radical of ACE is directly observed by transient diffuse reflectance spectroscopy. Preconditioning the silica gel by heating at 200°C in air partially removes physisorbed water from the silica surface and photochemical conversion of ACE is observed to occur faster.

Photochemistry of acenaphthene at a silica gel/air interface

The photochemical reactions of trans -stilbene and 1,1-diphenylethylene have been studied at a silica gel–air interface Irradiation of trans -stilbene leads to the formation of a substantial amount of two dimers, along with the formation of cis -stilbene, phenanthrene and a small amount of benzaldehyde Photochemical dimer formation from trans -stilbene on silica is promoted by inhomogeneous surface loading and slow surface diffusion Benzaldehyde arises from a Type II oxidation mechanism Irradiation of 1,1-diphenylethylene at a silica gel–air interface leads primarily to the formation of benzophenone The oxidation of 1,1-diphenylethylene occurs by a Type I mechanism, as previously proposed [J Org Chem 50 (1985) 149] The differences in observed photochemistry for these two substituted phenylethylenes on silica is attributed to two factors Isomerization of trans -stilbene competes efficiently with oxidation, whereas this pathway appears not to be important for 1,1-diphenylethylene Singlet molecular oxygen is shown to be quenched in solution and at the silica gel–air interface at a faster rate by cis -stilbene than by trans -stilbene or 1,1-diphenylethylene, thus providing an enhanced Type II oxidation pathway for stilbene

Photochemical reactions of trans-stilbene and 1,1-diphenylethylene on silica gel: mechanisms of oxidation and dimerization

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Spectroscopy and photochemistry of fluorene at a silica gel/air interface

Photochemistry of acenaphthene at a silica gel/air interface

Photochemical reactions of trans-stilbene and 1,1-diphenylethylene on silica gel: mechanisms of oxidation and dimerization