Volatilization Of Organic Compounds Research Articles

Molecular-Level Insights into the Relationship between Volatility of Organic Aerosol Constituents and PM2.5 Air Pollution Levels: A Study with Ultrahigh-Resolution Mass Spectrometry.

Volatility of organic aerosols (OAs) significantly influences new particle formation and the occurrence of particulate air pollution. However, the relationship between the volatility of OA and the level of particulate air pollution (i.e., particulate matter concentration) is not well understood. In this study, we compared the chemical composition (identified by an ultrahigh-resolution Orbitrap mass spectrometer) and volatility (estimated based on a predeveloped parametrization method) of OAs in urban PM2.5 (particulate matter with aerodynamic diameter ≤ 2.5 μm) samples from seven German and Chinese cities, where the PM2.5 concentration ranged from a light (14 μg m-3) to heavy (319 μg m-3) pollution level. A large fraction (71-98%) of compounds in PM2.5 samples were attributable to intermediate-volatility organic compounds (IVOCs) and semivolatile organic compounds (SVOCs). The fraction of low-volatility organic compounds (LVOCs) and extremely low-volatility organic compounds (ELVOCs) decreased from clean (28%) to heavily polluted urban regions (2%), while that of IVOCs increased from 34 to 62%. We found that the average peak area-weighted volatility of organic compounds in different cities showed a logarithmic correlation with the average PM2.5 concentration, indicating that the volatility of urban OAs increases with the increase of air pollution level. Our results provide new insights into the relationship between OA volatility and PM pollution levels and deepen the understanding of urban air pollutant evolution.

Production of ammonium bicarbonate from the condensate of the upgrading biogas-pipelines

Developing a suite of biofuels for different applications relies heavily on upgrading technologies to remove nitrogen compounds and carbon dioxide. Particularly in the upgrading of biogas to biomethane, simple water scrubbing is the most widely used technology for biogas upgrading. This technology can be synergistically implemented without the need for additional equipment for processing steps, although this design has not been conceived yet. Samples of biogas-pipeline condensates were collected from 3 different anaerobic digestion plants processing 3 different feedstocks (i.e., food waste, agrowaste, and manure) at 3 different locations in each plant (i.e., biodigester and postdigester condensate pits, digestate pasteurizer, and biogas booster and chiller). The methodology for the analysis of the 5-mL biogas-pipeline condensates was acid-base titration with 0.06 M hydrochloric acid and 0.13 M sodium hydroxide solutions as titrants, and induction of crystallization by cooling at 3 °C, adding up to 40 mL of acetone as antisolvent, and settling for 12 h. The results showed that the concentration of ammonium bicarbonate in the condensates ranged from 0.75 to 50 g/L. The most suitable location to enhance the upgradation of biogas, formation of condensate, and precipitation of ammonium bicarbonate was the pit after the anaerobic digester and before the biogas storage. The most concentrated condensate was retrieved from the biogas-pipeline coming out of the pasteurization tank, but the operation at 70.5 °C also led to volatilization of organic compounds that negatively affected the biogas quality. Future work aims to investigate coating and granulation of ammonium bicarbonate crystals to improve their stability and commercialization.

Volatility Parametrization of Low-Volatile Components of Ambient Organic Aerosols Based on Molecular Formulas.

Evaluating the volatility of organic compounds based solely on their molecular formulas would avoid tough demands in deriving molecular structures. Here, we deployed an iodide-adduct Long Time-of-Flight Chemical Ionization Mass Spectrometry (LToF-CIMS) combined with a Filter Inlet for Gases and AEROsols (FIGAERO) to investigate molecular formulas and thermograms of organic compounds on ambient particulate samples collected in the summer of 2021 in a suburban site of Shanghai and to estimate saturation vapor pressures of low- and semivolatile components of ambient organic aerosols. Then, a hierarchical cluster analysis and a subsequent classification of obtained clusters by similarity calculation were applied to the measured data set of molecular formulas and saturation vapor pressures of organic aerosols with at least a 2/3 appearance frequency, together with a similar data set collected at a rural site in the Beijing-Tianjin-Hebei region during the winter of 2018 (Ren et al., 2018), to classify all compounds into multiple groups. For each group of compounds, parametrizations between volatility and elemental composition were derived, and then relationships between each group of parameters and the mean O:C were established to achieve a volatility-molecular formula parametrization with the O:C as a key input. Statistical comparison of estimated volatilities of low-volatile organic compounds shows a much better performance of our parametrization than previous molecular formula-based ones.

Online measurement of highly oxygenated compounds from organic aerosol

Abstract. Highly oxygenated compounds are important contributors to the formation and growth of atmospheric organic aerosol and thus have an impact on Earth’s radiation balance and global climate. However, knowledge of the contribution of highly oxygenated compounds to organic aerosol and their fate after condensing into the particle phase has been limited by the lack of suitable detection techniques. Here, we present a new online method for measuring highly oxygenated compounds from organic aerosol. The method includes thermal evaporation of particles in a new inlet, the vaporization inlet for aerosols (VIA), followed by identification of the evaporated highly oxygenated compounds by a nitrate chemical ionization mass spectrometer (NO3-CIMS). The method does not require sample collection, enabling highly time-resolved measurements of particulate compounds. We evaluate the performance of the method by measuring the detection limit and performing background measurements. We estimate a detection limit of below 1 ng m−3 for a single compound and below 1 µg m−3 for SOA with the sampling setup used here. These detection limits can be improved upon by optimizing the flow setup. Furthermore, we detect hundreds of particulate highly oxygenated compounds from organic aerosol generated from different precursors. Our results are consistent with previous studies showing that the volatility of organic compounds decreases with increasing m/z ratio and level of oxygenation and that organic aerosol consists of monomers and oligomeric compounds. By comparing the gas- and particle-phase compounds, we found indications of potential particle-phase reactions occurring in organic aerosol. Future work will focus both on further improving the sampling design and on better understanding the evaporation dynamics of the system, but already these initial tests show that the VIA coupled to the NO3-CIMS is a promising method for investigating the transformations and fate of the compounds after condensing into the particle phase.

Non-Ionic Surfactant Recovery in Surfactant Enhancement Aquifer Remediation Effluent with Chlorobenzenes by Semivolatile Chlorinated Organic Compounds Volatilization.

Surfactant enhanced aquifer remediation is a common treatment to remediate polluted sites with the inconvenience that the effluent generated must be treated. In this work, a complex mixture of chlorobenzene and dichlorobenzenes in a non-ionic surfactant emulsion has been carried out by volatilization. Since this techhnique is strongly affected by the presence of the surfactant, modifying the vapour pressure, and activity coefficient, , a correlation between and surfactant concentration and temperature was proposed for each compound, employing the Surface Response Methodology (RSM). Volatilization experiments were carried out at different temperatures and gas flow rates. A good agreement between experimental and predicted remaining SVCOCs during the air stripping process was obtained, validating the thermodynamic parameters obtained with RSM. Regarding the results of volatilization, at 60 °C 80% of SVCOCs were removed after 6 h, and the surfactant capacity was almost completely recovered so the solution can be recycled in soil flushing.

Experimental Investigation on the Effects of Ethanol-Enhanced Steam Injection Remediation in Nitrobenzene-Contaminated Heterogeneous Aquifers

Steam injection is an effective technique for the remediation of aquifers polluted with volatile organic compounds. However, the application of steam injection technology requires a judicious selection of stratum media because the remediation effect of hot steam in heterogeneous layers with low permeability is not suitable. In this study, the removal effect of nitrobenzene in an aquifer was investigated through a series of two-dimensional sandbox experiments with different stratigraphic structures. Four types of alcohols were used during steam injection remediation to enhance the removal effect of nitrobenzene (NB)-contaminated heterogeneous aquifers. The principle of the removal mechanism of alcohol-enhanced organic compounds is that alcohols can reduce the surface tension of the contaminated water, resulting in Marangoni convection, thereby enhancing mass and heat transfer. The addition of alcohol may also reduce the azeotropic temperature of the system and enhance the volatility of organic compounds. The study revealed that all four alcohol types could reduce the surface tension from 72 mN/m to <30 mN/m. However, among these, only ethanol reduced the azeotropic temperature of NB by 15 °C, thereby reducing energy consumption and remediation costs. Therefore, ethanol was selected as an enhancing agent to reduce both surface tension and azeotropic temperature during steam injection. In the 2-D simulation tank, the interface between the low-and high-permeability strata in the layered heterogeneous aquifer had a blocking effect on steam transportation, which in turn caused a poor remediation effect in the upper low-permeability stratum. In the lens heterogeneous aquifer, steam flows around the lens, thereby weakening the remediation effect. After adding ethanol to the low-permeability zone, Marangoni convection was enhanced, which further enhanced the mass and heat transfer. In the layered and lens heterogeneous aquifers, the area affected by steam increased by 13% and 14%, respectively. Moreover, the average concentration of NB was reduced by 51% in layered heterogeneous aquifers and by 58% in low-permeability lenses by ethanol addition. These findings enhance the remediation effect of steam injection in heterogeneous porous media and contribute to improve the remediation efficiency of heterogeneous aquifers by steam injection.

Composite Encapsulation Enabled Superior Comprehensive Stability of Perovskite Solar Cells.

Solar cells based on organometal hybrid perovskites have exhibited promising commercialization potential owing to their high efficiency and low-cost manufacturing. However, the poor outdoor operational stability of perovskite solar cells restricted their practical application, and moisture permeation and organic compounds volatilization are realized as the main factors accelerating performance degradation. Herein, we developed a composite encapsulation, by sequentially depositing a compact Al2O3 layer and a hydrophobic 1H,1H,2H,2H-perfluorodecyltrichlorosilane layer on the completed device, to efficiently circumvent vapor permeability. Thus, the stability of the encapsulated perovskite solar cells was systematically investigated under simulated operational conditions. It was found that the MAPbI3 perovskite was prone to decay into solid PbI2 and organic vapor at high temperature or upon light illumination, and the decomposition was reversible in a well-encapsulated environment, resulting in reversible performance degradation and recovery. The enhanced thermal stability was ascribed to the competition between the perovskite decomposition and reverse synthesis. The as-prepared high-quality, multilayered encapsulation scheme demonstrated superior sealing property, and no obvious performance decline was observed when the device was stored under ambient air, continuous light illumination, double 85 condition (85 °C, 85% humidity), or even water immersion. Therefore, this work paves the way for a scalable and robust encapsulation strategy feasible to hybrid perovskite optoelectronics in a reproducible manner.

Raman spectroscopy of mini-CAST soot with various fractions of organic compounds: Structural characterization during heating treatment from 25 °C to 1000 °C

Soot particles undergo considerable changes in composition, morphology, as well as in internal structure during formation from the incipient particles to more mature aggregates, and still there is a lack of understanding of these mechanisms. In this study, soot produced by a mini-CAST soot generator was probed using Raman spectroscopy with focus on soot with large variation in size and fraction of organic compounds. The volatility of organic compounds and changes in internal bonding structures of the soot was surveyed by heating the samples from room temperature up to 1000 °C in a flow of inert N2 gas. The soot rich in organics showed more complex Raman spectra and stronger photoluminescence background. In particular, Raman signatures interpreted as the CH “out-of-plane” mode, ethers COC, and carbonyl CO groups were observed. During the heating treatment, these signatures disappeared, which was related to vaporization of the organics. Moreover, an enhancement of Raman band intensity of mature soot during heating treatment was observed for the first time. Our study thus brings new information on structural and compositional changes for soot during heating treatment in an inert atmosphere.

Increase in volatilization of organic compounds using air sparging through addition in alcohol in a soil-water system

This study developed a novel method to promote the remediation efficiency of air sparging. According to the enhanced-volatilization theory presented in this study, selected alcohols added to groundwater can highly enhance the volatilization amounts of organic compounds with high Henry’s law constants. In this study, the target organic compounds consisted of n-hexane, n-heptane, benzene, toluene, 1,1,2-trichloroethane, and tetrachloroethene. n-pentanol, n-hexanol, and n-heptanol were used to examine the changes in the volatilization amounts of organic compounds in the given period. Two types of soils with high and low organic matter were applied to evaluate the transport of organic compounds in the soil–water system. The volatilization amounts of the organic compounds increased with increasing alcohol concentrations. The volatilization amounts of the test organic compounds exhibited a decreasing order: n-heptanol>n-hexanol>n-pentanol. When 10mg/L n-heptanol was added to the system, the maximum volatilization enhancement rate was 18-fold higher than that in distilled water. Samples of soil with high organic matter might reduce the volatilization amounts by a factor of 5–10. In the present study, the optimal removal efficiency for aromatic compounds was approximately 98%.

Catalytic destruction of PCDD/Fs over vanadium oxide-based catalysts.

Vanadium oxide-based catalysts were developed for the destruction of vapour phase PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans). A vapour phase PCDD/Fs generating system was designed to supply stable PCDD/Fs steam with initial concentration of 3.2ngI-TEQNm(-3). Two kinds of titania (nano-TiO2 and conventional TiO2) and alumina were used as catalyst supports. For vanadium-based catalysts supported on nano-TiO2, catalyst activity is enhanced with operating temperature increasing from 160 to 300°C and then reduces with temperature rising further to 350°C. It is mainly due to the fact that high volatility of organic compounds at 350°C suppresses adsorption of PCDD/Fs on catalysts surface and then further inhibits the reaction between catalyst and PCDD/Fs. The optimum loading of vanadium on nano-TiO2 support is 5wt.% where vanadium oxide presents highly dispersed amorphous state according to the Raman spectra and XRD patterns. Excessive vanadium will block the pore space and form microcrystalline V2O5 on the support surface. At the vanadium loading of 5wt.%, nano-TiO2-supported catalyst performs best on PCDD/Fs destruction compared to Al2O3 and conventional TiO2. Chemical states of vanadium in the fresh, used and reoxidized VOx(5%)/TiO2 catalysts at different operating temperature are also analysed by XPS.

A refined method for the calculation of the Non-Methane Volatile Organic Compound emission estimate from Domestic Solvent Usage in Ireland from 1992 to 2014 – A case study for Ireland

This study describes a new methodology to calculate Non-Methane Volatile Organic Compounds from Domestic Solvent Use including Fungicides over the period 1992–2014. Improved emissions data compiled at a much more refined level can help policy-makers develop more effective policy’s to address environmental issues. However, a number of problems were found when member states attempt to use national statistics for Domestic Solvent Use including Fungicides. For instance, EMEP/EEA (2013) provides no guidance regarding which activity data should be used, resulting in emission estimates being potentially inconsistent and un-comparable. Also, previous methods and emission factors described in the EMEP/EEA (2013) guidebook do not exactly match data collected by state agencies. This makes using national statistics difficult. In addition, EMEP/EEA (2013) use broader categories than necessary (e.g. Cosmetics Aerosol/Non Aerosol) to estimate emissions while activity data is available at a more refined level scale (e.g. Personal Cleaning Products, Hair Products, Cosmetics, Deodorants and Perfumes). This can make identifying the drivers of emissions unclear. This study builds upon Tzanidakis et al. (2012) whereby it provides a method for collecting activity data from state statistics, developed country specific emission factors based on a survey of 177 Irish products and importantly, used a new method to account for the volatility of organic compounds found in commonly available domestic solvent containing products. This is the first study to account for volatility based on the characteristics of organic compounds and therefore is considered a more accurate method of accounting for emissions from this emission source. The results of this study can also be used to provide a simple method for other member parties to account for the volatility of organic compounds using sectorial adjustment factors described here. For comparison purposes, emission estimates were calculated using the Tier 1 approach currently used in the emission inventory, using activity data and emission factors unadjusted for volatility and adjusted for volatility. The unadjusted estimate is useful, because it demonstrates the failure to properly account for volatility can produce significantly over-estimated emissions from the Domestic Solvent Usage sector. Unadjusted emissions were found to be 30% lower than the EMEP/EEA (2013) Tier 1 period in 2014. Emissions were found to reduce a further 20.9% when the volatility of the organic compounds was included. This new method shows that member parties may be significantly overestimating emissions from Domestic Solvent Use including pesticides and further work should include refining organic compound content and the sectorial adjustment factor of products.

Emissions of Organic Compounds in Surfactant Solutions under Air Turbulence

The objective of this study was to investigate the effects of surfactants aggregating the gas-liquid interface on the volatilization rates of the organic compounds. The changes in the overall mass transfer coefficient (KOL) and concentration at gas-liquid interface of organic compounds in surfactant (dodecylbenzene sulfonic acid sodium, DBS) solutions under wind speed conditions were used to elucidate the results. The studied compounds consisted of aromatic compounds, benzene, toluene, ethylbenzene, m-dichlorobenzene, and propylbenzene with relatively higher Henry’s law constants (H) and water solubilities (Sw), and chlorinated pesticides, α-endosulfan, heptachlor epoxide, endrin, and dieldrin, with relatively lower H and Sw. Various surfactant concentrations, from 0 to 1000 mg/L under various wind speeds from 0 to 6.0 m/s, were used to examine the influence of the surfactant on the volatilization of the test organic compounds. The results indicated that the surfactant in the solution suppressed the volatilization of organic compounds. The degree of volatilization reduction was inversely proportional to the Sw values of the test organic compounds. The curve profiles for the KOL values of the organic compounds in the surfactant solutions, relative to the selected wind speed, were divided into the following two stages: the sharp-rise stage and the stable-linearity stage. The critical finding was that the surfactant markedly enhanced the concentrations of the low Sw compounds at the interface. The wind may cause an unexpected increase in the KOL value of the low Sw compound in the solution that contains a high surfactant concentration.

Experimental Study on Removal of Alkali-Metal and Incineration of High Concentration Organic Liquid Wastes

To resolve the operational problems such as agglomeration, fouling, sintering and corrosion due to low-melting eutectics formed by alkali and alkaline-earth metals in the wastewater, evaporation-crystallization method was used to remove alkali and alkaline-earth metals and decrease demand of assistant fuel before incineration. Salty concentrated liquid was recycled to be re-evaporated. The removal efficiency of Na+ in NaCl is 99.88%. The ratio of organic compounds volatilization is higher than 99.00%. Organic waste steam was incinerated in fluidized bed combustion (FBC). Combustion efficiency is influenced by bed temperature and air flux. As the temperature is increased from 650?C to 900?C at the air flux of 20m3/h, combustion efficiency is increased from 88.74% to 99.90%. When the air flux is increased from 20m3/h to 30m3/h, combustion efficiency is decreased, especially at the lower temperature. Reduction of the concentration of organic compounds can decrease the heat value of the steam, and then, reduce combustion efficiency.

Micellar Partitioning and Its Effects on Henry's Law Constants of Chlorinated Solvents in Anionic and Nonionic Surfactant Solutions

Micellar partitioning of volatile chlorinated hydrocarbons in surfactant solutions and its effects on vapor-liquid equilibrium is fundamental to the overall design and implementation of surfactant-enhanced aquifer remediation. Surfactant micelles greatly enhance contaminant recovery from the subsurface; however, the reduced volatility of organic compounds compromises the aboveground treatment of surfactant-laden wastewaters using air-stripping process. Batch equilibrium tests were performed to acquire micellar partition coefficients (Km) and apparent Henry's law constants (H*) of three prominent groundwater contaminants (tetrachloroethylene, trichloroethylene, cis-dichlorethylene) in the presence of two anionic surfactants (sodium dodecyl sulfate, SDS; sodium dodecylbenzene sulfonate, SDBS) and two nonionic surfactants (Triton X-100 and Tween 80). The H* values were significantly reduced in the presence of all four surfactants over their critical micelle concentrations (cmc's). On a cmc basis, the anionic surfactant SDS had the greatest effect on H*, followed by SDBS, Triton X-100, and Tween 80. Anionic surfactants decreased H* to an order of magnitude lower than nonionic surfactants, although nonionic surfactants decreased the H* at concentrations significantly lower than the anionic surfactants due to their lower cmc's. Nonionic surfactants present higher Km and molar solubilization ratio than anionic surfactants. Tetrachloroethylene has the highest Km values among three chlorinated solvents, which agrees well with the hydrophobicity (Kow) of these chemicals. An empirical correlation between log Km and log Kow is developed on the basis of data from this study and the Km values reported for a number of chlorinated and nonchlorinated hydrocarbons. Equilibrium data were also tested against three sets of models that describe the partitioning of volatile compounds in vapor-water-micelle phases. Applications of these models in experimentally determining Km from batch vapor-water equilibrium data are discussed.

Effect of Bubble‐Induced Surface Turbulence on Gas–Liquid Mass Transfer in Diffused Aeration Systems

Models that predict volatilization of organic compounds from wastewater treatment basins may underestimate emission rates if the surfaces are considered as quiescent. In reality, the water surface may be agitated by subsurface aeration, increasing mass transfer across the tank surface air-water interface. This study investigated the effect of turbulence, induced by diffused bubble aeration, on mass transfer at the water surface of a pilot aeration basin. The mass transfer of ammonia from an enclosed headspace over the basin to acidified water was measured when different diffuser types and airflow rates were applied. Oxygen-transfer tests were conducted immediately following each ammonia-transfer test. Increasing airflow rates through fine- and coarse-bubble diffusers had a significant effect on the ammonia mass-transfer rate. Experimental mass-transfer parameters (K(L)a's) for surface volatilization derived with aeration present were up to 48% higher than the K(L)a values for quiescent conditions over the range of conditions tested. No effect of diffuser type on ammonia transfer could be determined. The study results infer an effect on oxygen transfer into the water at the surface and potential transfer of volatile organic compounds, if present, from the water. The results of the ammonia mass-transfer experiments suggest that adjustments to the existing mass transfer correlations for surface volatilization from aeration basins may be in order. Such adjustments will have the greatest effect on predictions for the less volatile compounds, under conditions of low airflow rates.

Estimation of the volatilization of organic compounds from soil surfaces

Several simple models for the estimation of the half-life ( t 1/2) for the depletion of an organic chemical from a soil surface to air were examined. For moist surfaces, two models are proposed: the first requires knowledge of the soil/organic carbon partition coefficient ( K oc) and the Henry’s law constant ( H) and the second the vapor pressure ( P s) of the chemical involved. Due to uncertainties in the experimental K oc values those ones predicted by the group-contribution model of Meylan et al. [Environ. Sci. Technol. 26 (1992) 1560]—and proposed by the U.S. Environmental Protection Agency (EPA)—should be used. If reliable experimental P s values are not available, the first model is proposed, where in cases when H values are not available, predicted ones by the Bond-Contribution method of Meylan and Howard [Environ. Toxicol. Chem. 10 (1991) 1283]—and also proposed by EPA—can be used. In general, the agreement of the predicted t 1/2 values with the measured ones is within a factor of 3–5. Similar expressions, but with somewhat poorer results, are presented for dry field soils. In all cases, the obtained results represent a substantial improvement over those obtained with the currently used Dow method: t 1 / 2 = 1.58 · 10 - 8 ( K oc · S P S ) , where S is the solubility of the compound in water.

Volatile Organic Compounds Volatilization from Multicomponent Organic Liquids and Diffusion in Unsaturated Porous Media

Vapor phase diffusion is an important transport process in the unsaturated zone affecting evaporation of volatile organic compounds (VOCs) from pure and multicomponent organic liquids. To evaluate some widely used empirical relationships for the estimation of effective diffusion coefficients in the unsaturated zone and to assess the validity of Raoult9s Law during aging of organic mixtures, two series of laboratory-scale column experiments were performed using pure toluene, pure methyl tert-butyl ether (MTBE), and two multicomponent “kerosene-type” liquids containing four to seven compounds. The analytical one-dimensional solution of Fick9s Second Law described the diffusion process of pure compounds very well in two sands with different water contents. The effective diffusion coefficients obtained correspond well to a recently published empirical relationship (Moldrup et al., 2000); the capacity factors fitted indicate equilibrium partitioning of the solute between gas phase and water. A one-dimensional numerical model based on the combination of Fick9s Second Law and Raoult9s Law was used to predict the volatilization and the diffusion process from multicomponent organic liquids. Both the vapor phase diffusion process of the VOCs and the aging of the organic mixtures were predicted very well solely on the basis of effective diffusion coefficients estimated from the empirical relationship and assuming an ideal mixture (e.g., an activity coefficient of 1 in Raoult9s Law).

Volatile Organic Compounds Volatilization from Multicomponent Organic Liquids and Diffusion in Unsaturated Porous Media

Vapor phase diffusion is an important transport process in the unsaturated zone affecting evaporation of volatile organic compounds (VOCs) from pure and multicomponent organic liquids. To evaluate some widely used empirical relationships for the estimation of effective diffusion coefficients in the unsaturated zone and to assess the validity of Raoult's Law during aging of organic mixtures, two series of laboratory‐scale column experiments were performed using pure toluene, pure methyl tert‐butyl ether (MTBE), and two multicomponent “kerosene‐type” liquids containing four to seven compounds. The analytical one‐dimensional solution of Fick's Second Law described the diffusion process of pure compounds very well in two sands with different water contents. The effective diffusion coefficients obtained correspond well to a recently published empirical relationship (Moldrup et al., 2000); the capacity factors fitted indicate equilibrium partitioning of the solute between gas phase and water. A one‐dimensional numerical model based on the combination of Fick's Second Law and Raoult's Law was used to predict the volatilization and the diffusion process from multicomponent organic liquids. Both the vapor phase diffusion process of the VOCs and the aging of the organic mixtures were predicted very well solely on the basis of effective diffusion coefficients estimated from the empirical relationship and assuming an ideal mixture (e.g., an activity coefficient of 1 in Raoult's Law).

Volatile Organic Compounds Volatilization from Multicomponent Organic Liquids and Diffusion in Unsaturated Porous Media

Vapor phase diffusion is an important transport process in the unsaturated zone affecting evaporation of volatile organic compounds (VOCs) from pure and multicomponent organic liquids. To evaluate some widely used empirical relationships for the estimation of effective diffusion coefficients in the unsaturated zone and to assess the validity of Raoult's Law during aging of organic mixtures, two series of laboratory-scale column experiments were performed using pure toluene, pure methyl tert-butyl ether (MTBE), and two multicomponent “kerosene-type” liquids containing four to seven compounds. The analytical one-dimensional solution of Fick's Second Law described the diffusion process of pure compounds very well in two sands with different water contents. The effective diffusion coefficients obtained correspond well to a recently published empirical relationship (Moldrup et al., 2000); the capacity factors fitted indicate equilibrium partitioning of the solute between gas phase and water. A one-dimensional numerical model based on the combination of Fick's Second Law and Raoult's Law was used to predict the volatilization and the diffusion process from multicomponent organic liquids. Both the vapor phase diffusion process of the VOCs and the aging of the organic mixtures were predicted very well solely on the basis of effective diffusion coefficients estimated from the empirical relationship and assuming an ideal mixture (e.g., an activity coefficient of 1 in Raoult's Law).

Distribution and Volatilization of Organic Compounds Following Uptake by Hybrid Poplar Trees

ABSTRACT Hybrid poplar trees were exposed to eleven organic compounds in hydroponic systems. The eleven contaminants were common pollutants with a wide range of physio-chemical properties such as the octanol-water partition coefficient, Henry's constant, vapor pressure, and molecular weight. Contaminants, 14C-labeled, were introduced into the root zone, and contaminant transport and fate were examined. Aqueous concentrations were monitored throughout each experiment as was vapor phase concentrations in the air stream passing over the leaves. At experiment conclusion, plant tissues were oxidized to determine 14C concentrations. The uptake, distribution, and volatilization of these contaminants varied greatly among the 11 contaminants in the study. Uptake and translocation of the contaminants ranged from < 0.3% (of the applied 14C-labeled compound) for 1,2,4-trichlorobenzene to 20% for benzene. Volatile compounds were volatilized from the leaves. Volatilization in the transpiration stream was related to the vapor pressure of the compound. The fate and transport mechanisms investigated in this study provide valuable insight into the potential fate of contaminants in full-scale phytoremediation.