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The photodegradation of benzo[e]pyrene (BeP), a ubiquitous polycyclic aromatic hydrocarbon (PAH) contaminant, was investigated in solution and adsorbed on surfaces modeling the atmospheric particulate matter to provide fundamental information that could help to clarify its fate in the atmosphere. Diones, diols, and hydroxy derivatives were identified as the major photoproducts of BeP irradiated under simulated atmospheric conditions. The relative distribution of the products and the photodegradation rates of BeP were affected by the average pore size of the surface. Major photoproducts characterized in samples adsorbed on silica gel and alumina surfaces were not observed in irradiated solutions of BeP in hexane. In acetonitrile, the photodegradation rate was faster than in hexane, and one of the diones was observed. Different photoreaction pathways seem to take place in polar versus nonpolar microenvironments.

Benzo[e]pyrene (BeP) is a widespread polycyclic aromatic hydrocarbon found principally in highly polluted areas. The study of its photochemistry is important because of its possible toxic nature and its potential for phototransformation into biologically active products. We studied the primary photophysical and photochemical degradation processes of BeP, both in solution and adsorbed on silica gel and alumina, acting as models for the atmospheric particulate matter. The radical cation of BeP was characterized as an intermediate species during the photodegradation of BeP in polar solvents and adsorbed on the surfaces. The photoionization process was monophotonic, and once the radical cation was formed, it could react with water or oxygen to yield mainly diones, alcohols, and diols. In alumina, the radical yield was small, in accordance with the low photoreactivity observed on this surface. Two triplet-triplet absorption bands at 350 and 560 nm were observed in the time-resolved spectra of adsorbed BeP and in solution under nitrogen atmosphere. The BeP's triplet state, however, did not play an important role in its photoreaction pathway. The surface's pore size and the coadsorbed water affected the yields and kinetics of the intermediates but not the photodegradation mechanism.

The global minimum-energy and other significant structures of HCl(NH3)n (n=1–4) clusters have been identified by ab initio Monte Carlo simulated annealing. Geometries of the isomers were refined in density functional theoretical and Hartree–Fock plus second-order Møller–Plesset perturbation theoretical calculations. The energy orderings were confirmed in single-point higher-level calculations. While for HCl(NH3) only one hydrogen-bonded structure was found, for the larger clusters both ionic and molecular structures exist. Stabilization by hydrogen bonding is found to be less important in the ammonia clusters than in water clusters of similar size.

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Absorption and fluorescence emission spectra of the polycyclic aromatic hydrocarbons benzo [a] pyrene (BaP) and benzo[e]pyrene (BeP) in solution and adsorbed on silica have been obtained and compared to examine the spectroscopic effects of clustering. Molecular mechanics calculations with the UFF potential were done to optimize monomer, dimer and trimer geometries, and energy differences were determined by MP2/6-31G* calculations. Fluorescence emission spectra of adsorbed BeP and BaP display a red shift that progresses with increased loading, and the two differ in their photodegradation kinetics. The experimental and theoretical results are found to be consistent.

In advanced water treatment processes, the degradation efficiency of contaminants depends on the reactivity of the hydroxyl radical toward a target micropollutant. The present study predicts the hydroxyl radical rate constant in water (k ) for 118 emerging micropollutants, by means of quantitative structure-property relationships (QSPR). The conformation-independent QSPR approach is employed, together with a large number of 15,251 molecular descriptors derived with the PaDEL, Epi Suite, and Mold2 freewares. The best multivariable linear regression (MLR) models are found with the replacement method variable subset selection technique. The proposed five-descriptor model has the following statistics for the training set: [Formula: see text], RMS = 0.21, while for the test set is [Formula: see text], RMS = 0.11. This QSPR serves as a rational guide for predicting oxidation processes of micropollutants.

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