A new approach for estimating emissions of organic solutes and organic solvents under wind speeds

A new approach is developed to predict the volatilization loss of the pure liquid and the volatilization rates of organic solutes with different Henry's law constants (H) under wind speed. The tested compounds include eight volatile organic compounds for pure liquid and the forty-one organic solutes with different H compounds are divided into three groups that span seven H orders. The wind speed is set from 0 to 6.0 ms^?1. A characteristic parameter ε was established to estimate volatilization loss of pure organic compounds. The mass transfer coefficient (K_OL) ratios of the organic solutes, under both wind speed and still conditions, are applied to describe the volatilization characteristics of the selected solutes. The curve profile for K_OL ratios and ε values relative to the selected wind speed can be divided into two stages, the sharp-rise stage and the stable-linearity stage. The critical finding is the ε values for the different organic compounds under a specific wind speed approach a constant. The changes in the curve profile of the K_OL ratios are similar to the ε values of the pure organic compounds. It is also found the relatively lower H compounds exhibit a sensitive wind effect on the K_OL ratios. The K_OL ratios of the relatively higher H compounds indicate a similar linear increase with the increasing wind speed in the two stages. Accordingly, concentrations of the organic compounds at the interface are thought to the primary factor. The obtained results could be a good reference to estimate volatilization loss of the organic solutes or the organic solvents under different wind speed conditions.     

Method for predicting photocatalytic oxidation rates of organic compounds

In designing a photocatalytic oxidation (PCO) system for a given air pollution source, destruction rates for volatile organic compounds (VOCs) are required. The objective of this research was to develop a systematic method of predicting PCO rate constants by correlating rate constants with physical-chemical characteristics of compounds. Accordingly, reaction rate constants were determined for destruction of volatile organics over a titanium dioxide (TiO2) catalyst in a continuous mixed-batch reactor. It was found that PCO rate constants for alkanes and alkenes vary linearly with gas-phase ionization potential (IP) and with gas-phase hydroxyl radical reaction rate constant. The correlations allow rates of destruction of compounds not tested in this research to be predicted based on physical-chemical characteristics.     

Modeling effects of moisture content and advection on odor causing VOCs volatilization from stored swine manure

Two models for evaluating the contents and advection of manure moisture on odor causing volatile organic compounds (VOC-odor) volatilization from stored swine manure were studied for their ability to predict the volatilization rate (indoor air concentration) and cumulative exposure dose: a MJ-I model and a MJ-II model. Both models simulating depletion of source contaminant via volatilization and degradation based on an analytical model adapted from the behavior assessment model of Jury et al. In the MJ-I model, manure moisture movement was negligible, whereas in the MJ-II model, time-dependent indoor air concentrations was a function of constant manure moisture contents and steady-state moisture advection. Predicted indoor air concentrations and inhaled doses for the study VOC-odors of p-cresol, toluene, and p-xylene varied by up to two to three orders of magnitude depending on the manure moisture conditions. The sensitivity analysis of both models suggests that when manure moisture movement exists, simply MJ-I model is inherently not sufficient to represent a more generally volatilization process, which can even become stringent as moisture content increases. The conclusion illustrates how one needs to include a wide variety of manure moisture values in order to fully assess the complex volatilization mechanisms that are present in a real situation.     

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.     

An alternative method for predicting organic solute volatilization rates under gas and liquid turbulence

A method for predicting organic compound volatilization rates under turbulent liquid and gas conditions is developed. The reference compounds are classified according to their physico-chemical properties. The mass transfer coefficient (K(OL)) ratios for organic solutes to the reference compounds are constant for a wide range of environmental conditions, including liquid or air turbulence, or both at once. The obtained results indicate that when the environmental conditions are the same the determination of the volatilization rates is strongly dependent on the solute properties and the chemical structure. The presented method can more effectively estimate the volatilization rates of the solutes than the traditional one under various environmental conditions especially for low volatility solutes. The advantages and disadvantages of the traditional method are also discussed.     

Modeling effects of moisture content and advection on odor causing vocs volatilization from stored swine manure

Abstract

Two models for evaluating the contents and advection of manure moisture on odor causing volatile organic compounds (VOC‐odor) volatilization from stored swine manure were studied for their ability to predict the volatilization rate (indoor air concentration) and cumulative exposure dose: a MJ‐I model and a MJ‐II model. Both models simulating depletion of source contaminant via volatilization and degradation based on an analytical model adapted from the behavior assessment model of Jury et al. In the MJ‐I model, manure moisture movement was negligible, whereas in the MJ‐II model, time‐dependent indoor air concentrations was a function of constant manure moisture contents and steady‐state moisture advection. Predicted indoor air concentrations and inhaled doses for the study VOC‐odors of p‐cresol, toluene, and p‐xylene varied by up to two to three orders of magnitude depending on the manure moisture conditions. The sensitivity analysis of both models suggests that when manure moisture movement exists, simply MJ‐I model is inherently not sufficient to represent a more generally volatilization process, which can even become stringent as moisture content increases. The conclusion illustrates how one needs to include a wide variety of manure moisture values in order to fully assess the complex volatilization mechanisms that are present in a real situation.     

Modelling pesticide volatilization after soil application using the mechanistic model Volt'Air

Volatilization of pesticides participates in atmospheric contamination and affects environmental ecosystems including human welfare. Modelling at relevant time and spatial scales is needed to better understand the complex processes involved in pesticide volatilization. Volt'Air-Pesticides has been developed following a two-step procedure to study pesticide volatilization at the field scale and at a quarter time step. Firstly, Volt'Air-NH₃ was adapted by extending the initial transfer of solutes to pesticides and by adding specific calculations for physico-chemical equilibriums as well as for the degradation of pesticides in soil. Secondly, the model was evaluated in terms of 3 pesticides applied on bare soil (atrazine, alachlor, and trifluralin) which display a wide range of volatilization rates. A sensitivity analysis confirmed the relevance of tuning to K_h. Then, using Volt'Air-Pesticides, environmental conditions and emission fluxes of the pesticides were compared to fluxes measured under 2 environmental conditions. The model fairly well described water temporal dynamics, soil surface temperature, and energy budget. Overall, Volt'Air-Pesticides estimates of the order of magnitude of the volatilization flux of all three compounds were in good agreement with the field measurements. The model also satisfactorily simulated the decrease in the volatilization rate of the three pesticides during night-time as well as the decrease in the soil surface residue of trifluralin before and after incorporation. However, the timing of the maximum flux rate during the day was not correctly described, thought to be linked to an increased adsorption under dry soil conditions. Thanks to Volt'Air's capacity to deal with pedo-climatic conditions, several existing parameterizations describing adsorption as a function of soil water content could be tested. However, this point requires further investigation. Practically speaking, Volt'Air-Pesticides can be a useful tool to make decision about agricultural practices such as incorporation or for the estimation of overall pesticide volatilization rates, and it holds promise for time specific dynamics.     

Estimating biotransformation rate constants of organic chemicals from modeled and measured elimination rates.

In this study, biotransformation rate constants are estimated for a large set of organic compounds. Biotransformation (km) is considered part of the total elimination, further consisting of physico-chemical elimination to water (kw), depuration by feces (kf) and growth dilution (gamma). Existing models are used to estimate kw and kf, and gamma. The difference between measured elimination rate constants and the sum of predicted elimination rate constants for water, feces and growth indicates the ration of biotransformation in the total elimination. In all examined animal classes, polycyclic aromatic hydrocarbons seem to be metabolized at an intermediate rate. Because of the relative low hydrophobicity of some of the studied compounds, their physico-chemical elimination rate constant is relatively high, and the relative contribution of metabolism to total elimination of these compounds is therefore relatively low. Fish seem to be capable of metabolizing chlorodibenzo-p-dioxins and -furans, DDT, chloroanilines and phenol.     

Volatilization of 1,2-dibromo-3-chloropropane (DBCP) from soils.

The volatilization of DBCP from soils, as affected by the soil characteristics and application techniques, was studied in a laboratory experiment. The volatilization rate of DBCP applied in water was higher from sandy and silty loam soils than from clay soil. Water added after DBCP application acted as a soil cover, decreasing the volatilization rate. The results obtained with DBCP application in hexane to air-dry soils, indicate that adsorption could be an important factor in reducing the volatilization losses. Diffusion coefficients were calculated from the volatilization parameters, by using a simplified relationship between volatilization losses and diffusion through soil.     

Influence of membrane permeation on biodegradation kinetics of hydrophobic compounds

The relationship between membrane permeation rate and biodegradation rate has been investigated for alkyl esters of p-aminobenzoic acid. The pseudo-first order biodegradation rate constants of these compounds increase with increasing alkyl chain length, and increasing hydrophobicity, until alkyl chain lengths of greater than five carbon atoms, for which the biodegradation rate constants remain constant. This relationship between biodegradation rate constant and hydrophobicity parallels that of the permeabilities of lipid membranes and aqueous diffusion layers towards these compounds. This indicates that the rate-determining step in the biodegradation of these esters is their diffusion into bacterial cells, and that they then undergo rapid transformation.     

Volatilization of 1,2‐dibromo‐3‐chloropropane (DBCP) from soils

Abstract

The volatilization of DBCP from soils, as affected by the soil characteristics and application techniques, was studied in a laboratory experiment. The volatilization rate of DBCP applied in water was higher from sandy and silty loam soils than from clay soil. Water added after DBCP application acted as a soil cover, decreasing the volatilization rate. The results obtained with DBCP application in hexane to air‐dry soils, indicate that adsorption could be an important factor in reducing the volatilization losses.

Diffusion coefficients were calculated from the volatilization parameters, by using a simplified relationship between volatilization losses and diffusion through soil.     

Rate constants for reactions of singlet oxygen with phenols and other compounds in water

Rate constants for some environmentally important organic model compounds reacting with singlet oxygen in water have been determined in laboratory experiments using rose bengal as a sensitizer. Dimethylfuran, furfuryl alcohol, 2,3-dimethyl-2-butene and diethylsulfide react about three times faster in water than in non-aqueous solutions. Phenolic compounds react faster at higher pH values. Their rate constants exactly increase with their degree of dissociation. Rate constants for the ionized species of these phenolic compounds are greater than 10⁸M⁻¹s⁻¹. In natural surface water under solar irradiation reaction with singlet oxygen is important only for a few classes of especially reactive organic compounds.     

Behaviour of DDT under laboratory and outdoor conditions in Germany

Abstract

Experiments were conducted on adsorption, volatilization and UV‐degradation of p,p'‐DDT on soil surface, and leaching and degradation in sand columns. p,p'‐DDT was shown to adsorb stronger to soils with higher organic content. UV irradiation at 290 nm for 10 hours mineralized less than 0.1% of DDT in soil.

Results show that only 0.1% of DDT volatilized in a sun‐exposed semi‐closed quartz system. Polar compounds accounted from 1.4% after 55 days. The rate of volatilization and degradation in an open system was much higher; only 15% DDT and 7% DDE were recovered after 6 weeks in the organic extract. p,p'‐DDT was adsorbed to a great extent on the top layers of sand columns; 86% in the top 8 cm.     

Kinetic model for phenolic compound oxidation by Fenton's reagent

A kinetic model is developed for the oxidation of phenolic compounds by Fenton's reagent. In the first stage a rigorous kinetic model is applied to calculate the different kinetic rate constants for the oxidation process of p-hydroxybenzoic acid. In a second phase a competitive method is applied to calculate these kinetic constants for another 10 phenolic compounds present in agroindustrial and pulp paper wastewaters. These 10 phenolic compounds were: beta-resorcylic acid, 3-(4-hydroxyphenyl)-propionic acid, ferulic acid, protocatechuic acid, caffeic acid, p-coumaric acid, vanillic acid, syringic acid, veratric acid and 3,4,5-trimethoxybenzoic acid.     

Atmospheric Chemistry of Toxic Contaminants 1. Reaction Rates and Atmospheric Persistence

Using structure-reactivity relationships between reaction rate constants and ionlzatlon potentials for structural homologues, estimates are presented for the rate constants of the reactions of ozone, the hydroxyl radical, and the nitrate radical with forty toxic air contaminants for which no or little data are available. These rate constants are in turn used to estimate the atmospheric persistence of saturated allphatics, unsaturated allphatics, and aromatic toxic organics. The corresponding atmospheric half-lives for removal by chemical reactions range from a few hours for the most reactive toxics (chloroprene, hexachlorocyclo-pentadiene, cresols, nitrosamines, maleic anhydride) to several months for the least reactive compounds (nitrobenzene, methyl bromide, phosgene).     

Dissipation of triadimefon on the solid/gas interface.

The dissipation of triadimefon, as pure solid and in the Bayleton 5 commercial formulation, was studied under controlled and natural conditions. Volatilization and photodegradation were shown to be the main dissipation processes. The volatilization results can be described by an empirical model assuming exponential decay of the volatilization rate. The filler of the commercial formulation is determinant for the volatilization but has little effect on the photodegradation rates. The main photoproducts were identified and a reaction mechanism proposed.     

Kinetics of phenanthrene desorption from activated carbons to water

We determined the kinetics of phenanthrene desorption from three activated carbons to water using Tenax beads as an infinite sink for organic compounds in water. Desorption kinetic data very well fitted a biphasic kinetic model based on the presence of two different adsorption sites, viz. low-energy sites and high-energy sites. Rate constants for desorption to water from these two types of sites in the three activated carbons did not reveal a relation with activated carbon grain size. These rate constants were comparable to those for desorption of various organic compounds from hard carbon in various sediments.     

Prediction of pesticide volatilization with PELMO 3.31

In the current EU risk assessment for pesticide registration, the European Community requires prediction of the concentration of each pesticide in air. A number of mathematical models are used to assess the fate of pesticides in groundwater, surface water and soil. PELMO 3.20 calculates the volatilization fluxes from bare soil and was improved in the new version PELMO 3.31 to include the effect of temperature and sorption in dry soil. The objective of this study was to evaluate the new version of PELMO 3.31 in predicting the pesticide volatilization under field conditions. Procymidone, malathion, and ethoprophos were the test compounds in two different seasons (autumn and winter). Comparing simulation results obtained with PELMO 3.31, after calibration, with the previous version PELMO 3.20 shows that the estimated volatilization results seems improved for malathion, similar or slightly overestimating in the warmer season for ethoprophos, and similar or slightly underestimating in the colder season for procymidone. The new release of PELMO allows a more accurate estimation of pesticides volatilization from soil as function of meteorological factors, especially for medium or low volatility pesticides. Some difficulties remain, such as the determination of the active air layer and the sorption increment with the soil drying.     

Reaction rates and intermediates of chlorinated organic compounds in water and soil

Degradation reactions of thirteen chlorinated organic compounds were investigated in a water system and a water-soil system. Three compounds were degraded following the first order rate equation regardless of pH, and five compounds were degraded following the second order rate equation with a concentration of hydroxide ion in alkaline solution.The reaction rate constants and the activation energies of the reactions were obtained, and the intermediates were determined quantitatively for the eight compounds.From the result of the degradation of 1,1,1-trichloroethane in the water-soil system, it was found that 1,1,1 trichloroethane did not react on the soil surface and only reacted in the water phase.     

Monitoring of organochlorine pesticide residues in the Indian marine environment.

Organochlorine pesticide residues in sediment and fish samples collected from the east and west coasts of India are presented. HCH isomers and DDT and its metabolites are the predominantly identified compounds in most of the samples. Despite the higher quantity of consumption, HCH and DDT levels in fish in India were lower than those in temperate countries suggesting a lower accumulation in tropical fish, which could be due to rapid volatilization and degradation of these insecticides in the tropical environment. The predominance of alpha- and beta-HCH reflect the use of technical grade HCH in India. The high temperature in the tropics also enhances the elimination rate of chemicals in fish, as the biological half-lives of semivolatile compounds such as DDT are short at high temperature.