Uptake of Aromatic Hydrocarbon Vapors (Benzene and Phenanthrene) at the Air-Water Interface of Micron-Size Water Droplets

Abstract

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 phenan-threne vapor greater than that predicted by bulk (air-water)-phase equilibrium was observed for diameters less than 200 μm, 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, α = (1.4 ± 0.4) × 10^?2 was observed for the highly surface-active (hydrophobic) phenanthrene, whereas a small α = (9.7 ± 1.8) × 10^?5 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.     

Heterogeneous oxidation by ozone of naphthalene adsorbed at the air-water interface of micron-size water droplets

The mass transfer of naphthalene vapor to water droplets in air was studied in the presence of ozone (O3) in the gas phase. A falling droplet reactor with water droplets of diameters 55, 91, and 182 microm was used for the study. O3 reacted with naphthalene at the air-water interface, thereby decreasing the mass transfer resistance and increasing the rate of uptake of naphthalene into the droplet. A Langmuir-Hinshelwood reaction mechanism at the air-water interface satisfactorily described the surface reaction. The first-order surface reaction rate constant, ks, increased with decreasing droplet size. Three organic intermediates were identified in the aqueous phase as a result of ozonation of naphthalene at the surface of the droplet indicating both peroxidic and nonperoxidic routes for ozonation. The presence of an organic carbon surrogate (fulvic acid) increased both the partition constant of naphthalene and the surface reaction rate of O3. The heterogeneous oxidation of naphthalene by O3 on the droplet was 15 times faster than the homogeneous oxidation by O3 in the bulk air phase, whereas it was only 0.08 times the homogeneous gas-phase oxidation by hydroxyl radicals under atmospheric conditions.     

Seasonal trend of fog water chemical composition in the Po Valley

Fog frequency in the Po Valley, Northern Italy, can be as high as 30% of the time in the fall-winter season. High pollutant concentrations have been measured in fog water samples collected in this area over the past few years. The combined effects of high fog occurrence and high pollutant loading of the fog droplets can determine, in this area, appreciable chemical deposition rates. An automated station for fog water collection was developed, and deployed at the field station of S. Pietro Capofiume, in the eastern part of the Po Valley for an extended period: from the beginning of November 1989 to the end of April 1990. Time-resolved sampling of fog droplets was carried out during all fog events occurring in this period, and chemical analyses were performed on the collected samples. Statistical information on fog occurrence and fog water chemical composition is reported in this paper, and a tentative seasonal deposition budget is calculated for H+, NH4+, NO3- and SO4(2-) ions. The problems connected with fog droplet sampling in sub-freezing conditions are also addressed in the paper.     

Solubilization, solution equilibria, and biodegradation of PAH's under thermophilic conditions

Biodegradation rates of PAHs are typically low at mesophilic conditions and it is believed that the kinetics of degradation is controlled by PAH solubility and mass transfer rates. Solubility tests were performed on phenanthrene, fluorene and fluoranthene at 20 degrees C, 40 degrees C and 60 degrees C and, as expected, a significant increase in the equilibrium solubility concentration and of the rate of dissolution of these polycyclic aromatic hydrocarbons (PAHs) was observed with increasing temperature. A first-order model was used to describe the PAH dissolution kinetics and the thermodynamic property changes associated with the dissolution process (enthalpy, entropy and Gibb's free energy of solution) were evaluated. Further, other relevant thermodynamic properties for these PAHs, including the activity coefficients at infinite dilution, Henry's law constants and octanol-water partition coefficients, were calculated in the temperature range 20-60 degrees C. In parallel with the dissolution studies, three thermophilic Geobacilli were isolated from compost that grew on phenanthrene at 60 degrees C and degraded the PAH more rapidly than other reported mesophiles. Our results show that while solubilization rates of PAHs are significantly enhanced at elevated temperatures, the biodegradation of PAHs under thermophilic conditions is likely mass transfer limited due to enhanced degradation rates.     

Plant uptake, accumulation and translocation of phenanthrene and pyrene in soils

Uptake, accumulation and translocation of phenanthrene and pyrene by 12 plant species grown in various treated soils were comparatively investigated. Plant uptake and accumulation of phenanthrene and pyrene were correlated with their soil concentrations and plant compositions. Root or shoot accumulation of phenanthrene and pyrene in contaminated soils was elevated with the increase of their soil concentrations. Significantly positive correlations were shown between root concentrations or root concentration factors (RCFs) of phenanthrene and pyrene and root lipid contents. The RCFs of phenanthrene and pyrene for plants grown in contaminated soils with initial phenanthrene concentration of 133 mgkg(-1) and pyrene of 172 mgkg(-1) were 0.05-0.67 and 0.23-4.44, whereas the shoot concentration factors of these compounds were 0.006-0.12 and 0.004-0.12, respectively. For the same soil-plant treatment, shoot concentrations and concentration factors of phenanthrene and pyrene were generally much lower than root. Translocations of phenanthrene and pyrene from shoots to roots were undetectable. However, transport of these compounds from roots to shoots usually was the major pathway of shoot accumulation. Plant off-take of phenanthrene and pyrene only accounted for less than 0.01% of dissipation enhancement for phenanthrene and 0.24% for pyrene in planted versus unplanted control soils, whereas plant-promoted biodegradation was the predominant contribution of remediation enhancement of soil phenanthrene and pyrene in the presence of vegetation.     

Heterogeneous Oxidation by Ozone of Naphthalene Adsorbed at the Air-Water Interface of Micron-Size Water Droplets

Abstract

The mass transfer of naphthalene vapor to water droplets in air was studied in the presence of ozone (O₃) in the gas phase. A falling droplet reactor with water droplets of diameters 55, 91, and 182 μm was used for the study. O₃ reacted with naphthalene at the air-water interface, thereby decreasing the mass transfer resistance and increasing the rate of uptake of naphthalene into the droplet. A Langmuir-Hinshelwood reaction mechanism at the air-water interface satisfactorily described the surface reaction. The first-order surface reaction rate constant, k_s, increased with decreasing droplet size. Three organic intermediates were identified in the aqueous phase as a result of ozonation of naphthalene at the surface of the droplet indicating both peroxidic and nonperoxidic routes for ozonation. The presence of an organic carbon surrogate (fulvic acid) increased both the partition constant of naphthalene and the surface reaction rate of O₃. The heterogeneous oxidation of naphthalene by O₃ on the droplet was 15 times faster than the homogeneous oxidation by O₃ in the bulk air phase, whereas it was only 0.08 times the homogeneous gas-phase oxidation by hydroxyl radicals under atmospheric conditions.     

Uptake of polycyclic aromatic hydrocarbons by Trifolium pretense L. from water in the presence of a nonionic surfactant

A greenhouse study examined plant uptake of phenanthrene and pyrene, as representatives of polycyclic aromatic hydrocarbons (PAHs), from an aqueous solution containing a nonionic surfactant Tween 80. The uptake was conducted with 1.0 mg l(-1) phenanthrene and 0.12 mg l(-1) pyrene under a wide range of Tween 80 concentrations (0-105.6 mg l(-1)). Tween 80 at the test concentrations did not show any apparent phytotoxity toward the growth of red clover (Trifolium pretense L.). At concentrations generally lower than 13.2 mg l(-1), Tween 80 enhanced the plant uptake based on the concentrations and PCFs (plant concentration factors) of these two PAHs. When present at higher concentrations, Tween 80 inhibited the uptake of both PAH compounds by the tested plant. The maximal plant uptake was observed at 6.6 mg l(-1) Tween 80, in which PAH concentrations and PCFs were 18-115% higher than those in Tween 80-free controls. The total mass removal (off-take) of phenanthrene and pyrene by root or shoot increased initially and decreased thereafter with the increase in Tween 80 concentrations. Although shoot biomass was evidently larger than root, the off-take was much higher in root than shoot because of the larger root concentrations of these chemicals. Results from this study show promises for the potential efficacy of enhanced phytoremediation in PAH contaminated sites using surfactant amendment.     

Cooling Pond Steam Fog

This paper is responsive to needs to describe and predict the environmental effects from power plant cooling ponds. A study was made to determine atmospheric and pond surface conditions required for steam fog to occur from power plant cooling ponds, to define the dimensions of the fog, and to collect data on deposition of ice. Data, collected principally at the 4-Corners Plant over a three-year period, included water surface temperature, ambient meteorological conditions and occurrence and magnitude of steam fog and ice deposition. With strong winds, the fog extended onshore without lifting. With light winds, the fog extended some distance onshore but then lifted to form stratus. With almost calm winds, the steam fog lifted over the pond and drifted downwind as stratus. Steam fog was observed in winds to 28 mph, air-water temperature differences from 21.5° to 68°F and in atmospheric stability categories C, D, E, and F. A fog index number, Ar/(e_s — e_a)°F/mbs, was defined and used for data interpretation, where Ar is temperature of water less temperature of ambient air, e_s is the saturation vapor pressure of the ambient air and e_a is the actual vapor pressure of the ambient air. The probability of occurrence of steam fog as a function of the fog index number varied from 0.04 for an index number less than 10 to 1.00 for an index number greater than 90. From the data, if fog occurred, its extent along the ground was ≥100 feet 88% of the time, ≥500 feet 35% of the time, ≥1000 feet 18% of the time, and ≥5000 feet 12% of the time. If stratus occurred its extent above ground was ≥1 mile 91% of the time, ≥5 miles 55% of the time and ≥10 miles 36% of the time. Measurements showed that steam fog droplet sizes predominate in the 10 micron diameter size. Values of liquid water content up to 0.20 g/m³ were reported. Ice accretion data show build-up rates from 0.23 to 13 mm/hr of rime.     

Uptake of PAHs into polyoxymethylene and application to oil-soot (lampblack)-impacted soil samples

Polyoxymethylene (POM) is a polymeric material used increasingly in passive sampling of hydrophobic organic contaminants such as PAHs and PCBs in soils and sediments. In this study, we examined the sorption behavior of 12 PAH compounds to POM and observed linear isotherms spanning two orders of magnitude of aqueous concentrations. Uptake kinetic studies performed in batch systems for up to 54 d with two different volume ratios of POM-to-aqueous phase were evaluated with coupled diffusion and mass transfer models to simulate the movement of PAHs during the uptake process and to assess the physicochemical properties and experimental conditions that control uptake rates. Diffusion coefficients of PAHs in POM were estimated to be well correlated with diffusants' molecular weights as D(POM) proportional, variant(MW)(-3), descending from 2.3 x 10(-10) cm(2) s(-1) for naphthalene to 7.0 x 10(-11) cm(2) s(-1) for pyrene. The uptake rates for PAHs with log K(ow)<5.8 were controlled by the POM phase and the hydrophobicity of PAH compounds. For more hydrophobic PAH compounds, the aqueous boundary layer played an increasingly important role in determining the overall mass transfer rate. The POM partitioning technique was demonstrated to agree well with two other procedures for measuring PAH soil-water distribution coefficients in oil-soot (lampblack) containing soil samples.     

Quantifying simultaneous fluxes of ozone, carbon dioxide and water vapor above a subalpine forest ecosystem

Assessing the long-term exchange of trace gases and energy between terrestrial ecosystems and the atmosphere is an important priority of the current climate change research. In this regard, it is particularly significant to provide valid data on simultaneous fluxes of carbon, water vapor and pollutants over representative ecosystems. Eddy covariance measurements and model analyses of such combined fluxes over a subalpine coniferous forest in southern Wyoming (USA) are presented. While the exchange of water vapor and ozone are successfully measured by the eddy covariance system, fluxes of carbon dioxide (CO(2)) are uncertain. This is established by comparing measured fluxes with simulations produced by a detailed biophysical model (FORFLUX). The bias in CO(2) flux measurements is partially attributed to below-canopy advection caused by a complex terrain. We emphasize the difficulty of obtaining continuous long-term flux data in mountainous areas by direct measurements. Instrumental records are combined with simulation models as a feasible approach to assess seasonal and annual ecosystem exchange of carbon, water and ozone in alpine environments. The viability of this approach is demonstrated by: (1) showing the ability of the FORFLUX model to predict observed fluxes over a 9-day period in the summer of 1996; and (2) applying the model to estimate seasonal dynamics and annual totals of ozone deposition and carbon, and water vapor exchange at our study site. Estimated fluxes above this subalpine ecosystem in 1996 are: 195 g C m(-2) year(-1) net ecosystem production, 277 g C m(-2) year(-1) net primary production, 535 mm year(-1) total evapo-transpiration, 174 mm year(-1) canopy transpiration, 2.9 g m(-2) year(-1) total ozone deposition, and 1.72 g O(3) m(-2) year(-1) plant ozone uptake via leaf stomata. Given the large portion of non-stomatal ozone uptake (i.e. 41% of the total annual flux) predicted for this site, we suggest that future research of pollution-vegetation interactions should relate plant response to actively assimilated ozone by foliage rather than to total deposition. In this regard, we propose the Physiological Ozone Uptake Per Unit of Leaf Area (POUPULA) as a practical index for quantifying vegetation vulnerability to ozone damage. We estimate POUPULA to be 0.614 g O(3) m(-2) leaf area year(-1) at our subalpine site in 1996.     

Sorption of phenanthrene by soils contaminated with heavy metals

The fate of polycyclic aromatic hydrocarbons (PAHs) in soils with co-contaminants of heavy metals has yet to be elucidated. This study examined sorption of phenanthrene as a representative of PAHs by three soils contaminated with Pb, Zn or Cu. Phenanthrene sorption was clearly higher after the addition of heavy metals. The distribution coefficient (K(d)) and the organic carbon-normalized distribution coefficient (K(oc)) for phenanthrene sorption by soils spiked with Pb, Zn or Cu (0-1000 mg kg(-1)) were approximately 24% larger than those by unspiked ones, and the higher contents of heavy metals added into soils resulted in the larger K(d) and K(oc) values. The enhanced sorption of phenanthrene in the case of heavy metal-contaminated soils could be ascribed to the decreased dissolved organic matter (DOM) in solution and increased soil organic matter (SOM) as a consequence of DOM sorption onto soil solids. Concentrations of DOM in equilibrium solution for phenanthrene sorption were lower in the case of the heavy metal-spiked than unspiked soils. However, the decreased DOM in solution contributed little to the enhanced sorption of phenanthrene in the presence of metals. On the other hand, the sorbed DOM on soil solids after the addition of heavy metals in soils was found to be much more reactive and have far stronger capacity of phenanthrene uptake than the inherent SOM. The distribution coefficients of phenanthrene between water and the sorbed DOM on soil solids (K(ph/soc)) were about 2-3 magnitude larger than K(d) between water and inherent SOM, which may be the dominant mechanism of the enhanced sorption of phenanthrene by soils with the addition of heavy metals.     

Unsteady absorption of sulfur dioxide by an atmospheric water droplet with internal circulation

Unsteady absorption characteristics of sulfur dioxide by an atmospheric water droplet in motion are predicted numerically and analyzed theoretically to recognize the physical mass transport processes inside an aerosol droplet, which is frequently encountered in the atmosphere. Considering the absorption of sulfur dioxide by a droplet in cloud or fog with various velocities, three different Reynolds numbers, viz., Re_g=0.643, 1.287, and 12.87 are studied and compared with each other. The results indicate that for the Reynolds number of 0.643, sulfur dioxide always penetrates toward the droplet centerline throughout the entire absorption period. This is due to the mass transfer dominated by diffusion along the radial direction. In contrast, when the Reynolds number is 12.87, the strength of the vortex motion inside the droplet is strong enough. It results in that, most of the time the concentration contours parallel the streamlines and the lowest SO₂ concentration is located at the vortex center. As a consequence, the diffusion distance is reduced by a factor of three and the absorption time for the droplet reaching the saturated state is shortened in a significant way. With regard to an intermediate Reynolds number such as 1.287, a two-stage mass transfer process can be clearly identified. In the first stage, it is dominated by one-dimensional diffusion, in which over 50% sulfur dioxide is absorbed before the saturated state is reached. In the second stage, the vortex motion mainly controls the mass transfer. However, the contour core is inconsistent with the vortex center. This is because the characteristic time of mass diffusion is in a comparable state with that of droplet internal circulation. The present study elucidates that the strength of a droplet's internal motion plays a vital role in determining SO₂ absorption process.     

Laboratory studies on the uptake of aromatic hydrocarbons by ice crystals during vapor depositional crystal growth

Uptake of aromatic hydrocarbons (AH) by ice crystals during vapor deposit growth was investigated in a walk-in cold chamber at temperatures of 242, 251, and 260 K, respectively. Ice crystals were grown from ambient air in the presence of gaseous AH namely: benzene (C₆H₆), toluene (methylbenzene, C₇H₈), the C₈H₁₀ isomers ethylbenzene, o-, m-, p-xylene (dimethylbenzenes), the C₉H₁₂ isomers n-propylbenzene, 4-ethyltoluene, 1,3,5-trimethylbenzene (1,3,5-TMB), 1,2,4-trimethylbenzene (1,2,4-TMB), 1,2,3-trimethylbenzene (1,2,3-TMB), and the C₁₀H₁₄ compound tert.-butylbenzene. Gas-phase concentrations calculated at 295 K were 10.3–20.8 μg m⁻³. Uptake of AH was detected by analyzing vapor deposited ice with a very sensitive method composed of solid-phase micro-extraction (SPME), followed by gas chromatography/mass spectrometry (GC/MS).Ice crystal size was lower than 1 cm. At water vapor extents of 5.8, 6.0 and 8.1 g m⁻³, ice crystal shape changed with decreasing temperatures from a column at a temperature of 260 K, to a plate at 251 K, and to a dendrite at 242 K. Experimentally observed ice growth rates were between 3.3 and 13.3×10⁻³ g s⁻¹ m⁻² and decreased at lower temperatures and lower value of water vapor concentration. Predicted growth rates were mostly slightly higher.Benzene, toluene, ethylbenzene, and xylenes (BTEX) were not detected in ice above their detection limits (DLs) of 25 pg g_ice⁻¹ (toluene, ethylbenzene, xylenes) and 125 pg g_ice⁻¹ (benzene) over the entire temperature range. Median concentrations of n-propylbenzene, 4-ethyltoluene, 1,3,5-TMB, tert.-butylbenzene, 1,2,4-TMB, and 1,2,3-TMB were between 4 and 176 pg g_ice⁻¹ at gas concentrations of 10.3–10.7 μg m⁻³ calculated at 295 K. Uptake coefficients (K) defined as the product of concentration of AH in ice and density of ice related to the product of their concentration in the gas phase and ice mass varied between 0.40 and 10.23. K increased with decreasing temperatures. Values of Gibbs energy (ΔG) were between −4.5 and 2.4 kJ mol⁻¹ and decreased as temperatures were lowered. From the uptake experiments, the uptake enthalpy (ΔH) could be determined between −70.6 and −33.9 kJ mol⁻¹. The uptake entropy (ΔS) was between −281.3 and −126.8 J mol⁻¹ K⁻¹. Values of ΔH and ΔS were rather similar for 4-ethlytoluene, 1,3,5-TMB and tert.-butylbenzene, whereas 1,2,3-TMB showed much higher values.     

Effect of water content on transient nonequilibrium NAPL-gas mass transfer during soil vapor extraction

The effect of water content on the volatilization of nonaqueous phase liquid (NAPL) in unsaturated soils was characterized by one-dimensional venting experiments conducted to evaluate the lumped mass transfer coefficient. An empirical correlation based upon the modified Sherwood number, Peclet number, and normalized mean grain size was used to estimate initial lumped mass transfer coefficients over a range of water content. The effects of water content on the soil vapor extraction SVE process have been investigated through experimentation and mathematical modeling. The experimental results indicated that a rate-limited NAPL-gas mass transfer occurred in water-wet soils. A severe mass transfer limitation was observed at 61.0% water saturation where the normalized effluent gas concentrations fell below 1.0 almost immediately, declined exponentially from the initiation of venting, and showed long tailing. This result was attributed to the reduction of interfacial area between the NAPL and mobile gas phases due to the increased water content. A transient mathematical model describing the change of the lumped mass transfer coefficient was used. Simulations showed that the nonequilibrium mass transfer process could be characterized by the exponent beta, a parameter which described the reduction of the specific area available for NAPL volatilization. The nonequilibrium mass transfer limitations were controlled by the soil mean grain size and pore gas velocity, were well described by beta values below 1.0 at low water saturation, and were well predicted with beta values greater than 1.0 at high water saturation.     

Plant-accelerated dissipation of phenanthrene and pyrene from water in the presence of a nonionic-surfactant

Plant-accelerated dissipation of phenanthrene and pyrene in water in the presence of a nonionic-surfactant (Brij35) was studied. The mechanisms involved were evaluated, based on the investigation of plant uptake of these compounds from water with Brij35. The presence of ryegrass (Lolium multiflorum Lam) clearly enhanced the dissipation of tested PAHs in water with 0-296 mg l(-1) Brij35. The first-order rate constants (K), calculated from the first-order kinetic models for these PAH degradation (all significant at P < 0.05, n=8), of phenanthrene and pyrene in the presence of ryegrass were 16.7-50% and 47.1-108% larger than those of plant-free treatments, whereas half-lives (T1/2) of the former were 14.3-33.4% and 32.0-52.0% smaller than the latter, respectively. However, the promotion of PAH dissipation by ryegrass was found to significantly decrease with increasing Brij35 concentrations. In the range of 0-296 mg l(-1), low concentrations (< or = 74.0 mg l(-1)) of Brij35 generally enhanced plant uptake and accumulation of phenanthrene and pyrene, based on the observed plant concentrations and accumulated amounts of these chemicals from water. In contrast, Brij35 at relatively high concentrations (> or = 148 mg l(-1)) markedly restricted plant uptake of these PAHs. Plant accumulation of phenanthrene and pyrene accounted for 6.21-35.0% and 7.66-24.3% of the dissipation enhancement of these compounds from planted versus unplanted water bodies. In addition, plant metabolism was speculated to be another major mechanism of plant-accelerated dissipation of these PAHs in water systems. Results obtained from this study provided some insight with regard to the feasibility of phytoremediation for PAH contaminated water bodies with coexisted contaminants of surfactants.     

PCB mass transfer coefficients determined by application of a water surface sampler

A water surface sampler (WSS) was employed in combination with greased surface deposition plates (GSDPs) to measure the particulate dry deposition and gas exchange of polychlorinated biphenyls (PCBs) in Chicago, IL. Vapor phase PCB fluxes were calculated by subtracting the particulate fluxes obtained from GSDPs from total (particulate+gas) fluxes obtained from the WSS. Vapor phase PCB fluxes were divided by ambient air concentrations measured with a high volume sampler to calculate overall gas phase PCB mass transfer coefficients (K(G)). The calculated average PCB MTC was 0.54+/-0.47 cm s(-1). This experimentally determined average gas phase overall mass transfer coefficient, K(G), agreed well with the ones reported from studies using similar techniques and agreed well with modeled values obtained using MTC correlations developed for the WSS.     

Ionic liquid-containing semipermeable membrane devices for monitoring the polycyclic aromatic hydrocarbons in water

Ionic liquid-containing semipermeable membrane devices (IL-SPMDs) were developed to monitor the polycyclic aromatic hydrocarbons in water. Uptake kinetics of naphthalene, 1-methylnaphthalene, phenanthrene, pyrene, chrysene by layflat low-density polyethylene tubing (15 cm x 2 cm) filled with 0.5 ml 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid were studied in a laboratory continuous-flow system for the duration of 16 days. The device concentration factors were in the range of 830-7800 for the studied PAHs. The kinetic parameters of IL/water partition coefficients, analytes uptake rate constants and sampling rates were estimated using mathematical models. These parameters were used in the field experiment to estimate the concentrations of the PAHs in Lanzhou section of Yellow River in China, with the result in comparison with that obtained by triolein-SPMD.     

Remediation of PAH contaminated soils: application of a solid-liquid two-phase partitioning bioreactor

The feasibility of a two-step treatment process has been assessed at laboratory scale for the remediation of soil contaminated with a model mixture of polycyclic aromatic hydrocarbons (PAHs) (phenanthrene, pyrene, and fluoranthene). The initial step of the process involved contacting contaminated soil with thermoplastic, polymeric pellets (polyurethane). The ability of three different mobilizing agents (water, surfactant (Biosolve) and isopropyl alcohol) to enhance recovery of PAHs from soil was investigated and the results were compared to the recovery of PAHs from dry soil. The presence of isopropyl alcohol had the greatest impact on PAH recovery with approximately 80% of the original mass of PAHs in the soil being absorbed by the polymer pellets in 48 h. The second stage of the suggested treatment involved regeneration of the PAH loaded polymers via PAH biodegradation, which was carried out in a solid-liquid two-phase partitioning bioreactor. In addition to the PAH containing polymer pellets, the bioreactor contained a microbial consortium that was pre-selected for its ability to degrade the model PAHs and after a 14 d period approximately 78%, 62% and 36% of phenanthrene, pyrene, and fluoranthene, respectively, had been desorbed from the polymer and degraded. The rate of phenanthrene degradation was shown to be limited by mass transfer of phenanthrene from the polymer pellets. In case of pyrene and fluoranthene a combination of mass transfer and biodegradation rate might have been limiting.     

Characteristics of photocatalytic oxidation of toluene, benzene, and their mixture

The investigation of the photocatalytic oxidation (PCO) of multicomponent volatile organic compounds (VOCs) is very important to the application of PCO technology, because there is seldom a single VOC component in indoor air. In this paper, the characteristics of binary indoor VOCs, toluene and benzene, were experimentally studied using a mass transfer based method that we developed. The concentration ranges for toluene and benzene were 4.48-27.4 mg/m3 and 1.82-4.08 mg/m3, respectively. We found the following: (1) the PCO of each individual contaminant studied obeys the unimolecular form of the Langmuir-Hinshelwood (L-H) rate form; (2) the PCO of the binary contaminants follow the competitive adsorption L-H rate form; (3) the reaction-coefficient for PCO of individual contaminants differs from that in the competitive adsorption L-H rate form; and (4) the component impact factor of A to B, put forward in this paper, is a useful parameter describing the influence of A on the reaction coefficient of B, and it was found that the impact factor of toluene (a chemically active component) on benzene (a chemically stable component) is high, and the impact factor of benzene on toluene is low.     

Modelling photochemical reactions in atmospheric water droplets: An assessment of the importance of surface processes

The relative importance of surface versus bulk processes was computed in spherical water drops, based on the model photochemical reaction yielding phenol from benzene via the ^•OH radicals, formed on UV photolysis of nitrate. The coadsorption of benzene and nitrate at the droplet surface was taken into account by means of the Wagner–Onsager–Samaras interaction model. The results indicate that the surface accumulation of benzene and the coadsorption of benzene and nitrate, which substantially increase the value of the concentration product of the model species at the droplet surface compared to the bulk, would cause surface processes to play a very significant role, in particular in small drops (1 μm radius, as can be found in haze and mist). Under such circumstances, over 15% of phenol photoformation would take place in just 0.1% of the drop volume. Similar results are expected in the case of benzene hydroxylation and nitration on nitrite photolysis.