Adsorption of polycyclic aromatic hydrocarbons at the air–water interface: Molecular dynamics simulations and experimental atmospheric observations (original) (raw)
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Adsorption of aromatic hydrocarbons and ozone at environmental aqueous surfaces
The Journal of …, 2008
Adsorption of environmentally important aromatic molecules on a water surface is studied by means of classical and ab initio molecular dynamics simulations and by reflectionabsorption infrared spectroscopy. Both techniques show strong activity and orientational preference of these molecules at the surface. Benzene and naphtalene, which bind weakly to water surface with a significant contribution of dispersion interactions, prefer to lie flat on water but retain a large degree of orientational flexibility. Pyridine is more rigid at the surface. It is tilted with the nitrogen end having strong hydrogen bonding interactions with water molecules. The degree of adsorption and orientation of aromatic molecules on aqueous droplets has atmospheric implications for heterogenous ozonolysis, for which the Langmuir-Hinshelwood kinetics mechanism is validated. At higher coverages of aromatic molecules the incoming ozone almost does not come into contact with the underlying aqueous phase. This may rationalize the experimental insensitivity of the ozonolysis on the chemical nature of the substrate on which the aromatic molecules adsorb.
Journal of Chemical & …, 2002
Experimental data on the adsorption of polycyclic aromatic hydrocarbons (PAHs) at the gas-water interface is lacking. The inverse gas chromatography (IGC) technique with Chromosorb P NAW as the packing support was used to obtain the thermodynamic parameters for the adsorption of three aromatic compounds (benzene, naphthalene, and phenanthrene) at the gas-water interface. The partition constants at different temperatures were measured and used to compute the free energy, enthalpy, and entropy of adsorption using the Gibbs-Helmholtz equation. The enthalpy of adsorption at the gas-water interface for all three compounds was larger than the enthalpy of condensation and the enthalpy of aqueous solvation. This supports the prevailing "critical cluster" model for the dynamics of the transfer of compounds to the gas-water interface. The thermodynamics of adsorption at the gas-solid interface was more favorable than that at the gas-water interface. The partition constant at the gas-water interface was correlated with the subcooled liquid vapor pressure of the PAHs. The possible effect of gas-water partitioning of PAHs upon their wet deposition from the atmosphere is explored theoretically.
The Journal of Physical Chemistry …, 2010
A combination of Monte Carlo and molecular dynamics simulations was carried out to investigate the effect of 1-octanol surface coverage on the interfacial partitioning and behavior of polyaromatic hydrocarbons. Also, how the surface coverage of 1-octanol is related to its gas-phase density was examined. It was found that 1-octanol partitioned sparsely, preferring to lie flat at the water surface at low gas-phase concentrations. As the gas-phase concentration increased, the 1-octanol surface coverage increased rapidly, and it oriented more perpendicular to the water surface. The interfacial partitioning of polyaromatic hydrocarbons was enhanced significantly for larger ones, such as naphthalene and anthracene, when 1-octanol was present at the air-water interface, but benzene had a similar portioning for both cases. Naphthalene preferred to lie flat on the bare water surface, but with 1-octanol present, it oriented fairly perpendicular to the surface when close to the water surface and parallel to the surface when at the interface of 1-octanol and air.
Journal of the Air & Waste Management …, 2004
Uptake of aromatic hydrocarbon vapors (benzene and phenanthrene) by typical micrometer-sized fog-water droplets was studied using a falling droplet reactor at temperatures between 296 and 316 K. Uptake of phenanthrene vapor greater than that predicted by bulk (airwater)-phase equilibrium was observed for diameters less than 200 m, and this was attributed to surface adsorption. The experimental values of the droplet-vapor partition constant were used to obtain the overall mass transfer coefficient and the mass accommodation coefficient for both benzene and phenanthrene. Mass transfer of phenanthrene was dependent only on gas-phase diffusion and mass accommodation at the interface. However, for benzene, the mass transfer was limited by liquid-phase diffusion and mass accommodation. A large value of the mass accommodation coefficient, ␣ ϭ (1.4 Ϯ 0.4) ϫ 10 Ϫ2 was observed for the highly surface-active (hydrophobic) phenanthrene, whereas a small ␣ ϭ (9.7 Ϯ 1.8) ϫ 10 Ϫ5 was observed for the less hydrophobic benzene. Critical cluster numbers ranging from 2 for benzene to 5.7 for phenanthrene were deduced using the critical cluster nucleation theory for mass accommodation. The enthalpy of mass accommodation was more negative for phenanthrene than it was for benzene. Consequently, the temperature effect was more pronounced for phenanthrene. A linear correlation was observed for the enthalpy of accommodation with the excess enthalpy of solution. A natural organic carbon surrogate (Suwannee Fulvic acid) in the water droplet increased the uptake for phenanthrene and benzene, the effect being more marked for phenanthrene. A characteristic time constant analysis showed that uptake and droplet scavenging would compete for the fog deposition of phenanthrene, whereas deposition would be unimpeded by the uptake rate for benzene vapor. For both compounds, the characteristic atmospheric reaction times were much larger and would not impact fog deposition.
Competitive adsorption of polycyclic aromatic hydrocarbons on organo-zeolites
Microporous and Mesoporous Materials, 2007
Sorption of polycyclic aromatic hydrocarbons on organo-zeolites was investigated to determine sorbent-sorbate interaction. The hydrophobic character of the surface of the organo-zeolites was studied using in water vapor adsorption experiments. Water adsorption decreased with increasing stearyldimethylbenzylammoniumchloride (SDBAC) loading up to 75 mmol/kg, which is related to increasing sorbate hydrophobicity. With loadings above 75 mmol/kg (ECEC value), water vapor adsorption increased. Effects of adsorbent size, SDBAC loading and initial concentration of PAHs on the adsorption efficiency were also determined. The highest adsorption for the PAHs studied was achieved with OZ II 75 (OZ -organo-zeolite; II -particle size of 0.4-0.8 mm; 75 -mmol of surfactant/kg of zeolite). At a concentration of 20 lg/dm 3 the adsorption index for benz[a]anthracene was 100%. The smaller adsorption indexes for PAHs with lower partition coefficients, K ow , indicated that the adsorption is primarily hydrophobic. The number of bed volumes passed through the adsorbent before the first PAH appeared in the effluent was 770. Column experiments showed competitive adsorption among the PAHs with different hydrophobicities.
Pure and Applied Chemistry, 2009
The thermodynamics of adsorption of gaseous organic compounds such as polycyclic aromatic hydrocarbons (PAHs) on water films is reviewed and discussed. The various experimental methods available to determine the thermodynamic equilibrium constant and the structure-activity relationships to correlate and estimate the same are reviewed. The atmos pheric implications of the adsorption and oxidation of PAHs at the air-water interface of thin films of water such as existing in fog droplets, ice films, and aerosols are also enumerated.
Industrial & Engineering Chemistry Research, 2003
Polycyclic aromatic hydrocarbons (PAHs) from phenanthrene to benzo [g,h,i]perylene in airborne particles were measured in the winter of 2000 at three different sites within the metropolitan area of S* ao Paulo City (MASP), Brazil. It is one of the largest metropolitan areas in the world and has an unconventional mixture of vehicle types, in which a variety of gasoline blends, including oxygenated ones, are used. In this study, occurrence of PAH, meteorological conditions and inter and intrasite comparisons are presented. Overall, the results revealed low PAH levels due to rainfall episodes during the sampling period. Samples collected in the urban site presented the highest PAH concentrations (av. 3.10 ng m À3 ) when compared to those collected in the urban site with dense vegetation (av. 2.73 ng m À3 ) and in the forest area (av. 1.92 ng m À3 ). PAH measurements in tunnels with different types of vehicles were performed in order to suggest possible tracers of the vehicular emissions in S* ao Paulo. Pyrene followed by chrysene and fluoranthene were emitted mainly from gasohol vehicular motor exhausts, whereas chrysene, pyrene and benzo[a]anthracene were emitted mainly from gasohol and diesel vehicular motor exhausts. Some characteristic ratios from the tunnel measurements were used to identify vehicular sources in the atmosphere of the MASP. Although it is known that losses can occur both by evaporation and sublimation during sampling, measurements of higher molecular weight PAH compounds were taken into consideration due to their high recovery efficiency. r
Chemical Society Reviews, 2013
Polycyclic aromatic hydrocarbons (PAHs) are of considerable concern due to their well-recognised toxicity and especially due to the carcinogenic hazard which they present. PAHs are semi-volatile and therefore partition between vapour and condensed phases in the atmosphere and both the vapour and particulate forms undergo chemical reactions. This article briefly reviews the current understanding of vapour-particle partitioning of PAHs and the PAH deposition processes, and in greater detail, their chemical reactions. PAHs are reactive towards a number of atmospheric oxidants, most notably the hydroxyl radical, ozone, the nitrate radical (NO 3) and nitrogen dioxide. Rate coefficient data are reviewed for reactions of lower molecular weight PAH vapour with these species as well as for heterogeneous reactions of higher molecular weight compounds. Whereas the data for reactions of the 2-3-ring PAH vapour are quite extensive and generally consistent, such data are mostly lacking for the 4-ring PAHs and the heterogeneous rate data (5 and more rings), which are dependent on the substrate type and reaction conditions, are less comprehensive. The atmospheric reactions of PAH lead to the formation of oxy and nitro derivatives, reviewed here, too. Finally, the capacity of PAHs for long range transport and the results of numerical model studies are described. Research needs are identified.
Oil & Gas Science and Technology - Revue de l'IFP, 2006
carbures comme source possible de pollution atmosphérique -Les solutions d'hydrocarbures ne sont pas très souvent étudiées. Cependant, leur comportement est impliqué dans de nombreux mécanismes, en particulier les mécanismes environnementaux. Dans le présent article, nous présentons la synthèse de plusieurs travaux ayant trait au comportement superficiel, en particulier d'adsorption, de solutions non saturées de benzène et de cyclohexane. Il y est mis en évidence la coadsorption de nitrate de plomb, bien que celui-ci, en l'absence de molécules organiques dans la surface, ne s'adsorbe pas du tout. Ces données ont été obtenues essentiellement au moyen d'une technique rarement utilisée, la colonne à bulles, brièvement décrite ci-dessous. Celle-ci, en dépit des contraintes de sa mise en oeuvre, s'est révélée très utile dans l'étude de ces composés faiblement adsorbables, et peu actifs sur la tension de surface. L'étude des mélanges se fait directement, sans avoir à utiliser de modèle, ce qui est précieux pour des études environnementales. Les résultats obtenus établissent de façon convaincante que des mécanismes, tels que le pétillement, joints à la coadsorption, peuvent entraîner le passage de composés nocifs pour l'environnement, peu solubles, peu actifs sur la surface quand ils sont isolés, depuis l'eau jusque dans l'atmosphère.