Phenols and nitrophenols as tropospheric pollutants: Emissions from automobile exhausts and phase transfer in the atmosphere

Motor exhaust gas from an automobile motor, operated under stationary conditions with unleaded gasoline, was sampled with two different impinger bath methods. The samples were analyzed by gas chromatography/mass spectrometry (GC/MS) for phenol, cresols and nitrated phenols. Phenol and cresols were measured in the range of 80–220 nmol/L of exhaust gas from a noncatalyst engine, and nitrated phenols were found in the range of 9–36 nmol/L. A large reduction of total phenols down to 7% and less was observed when the engine was operated with a regulated three-way catalytic converter. The result of this study shows that exhaust gas sampling of phenols with alkaline aqueous impinger solutions leads to an underestimation of phenol emissions, since phenols are not stable under high-pH conditions. In order to better assess the environmental fate of nitrated phenols, laboratory experiments were conducted to measure the Henry's law constants of a series of nitrated phenols. For that purpose an apparatus for dynamic determination of the Henry's law constants was constructed and successfully used. Special emphasis was put on temperature dependence of the Henry's law constants.     

The Distribution of PCB's and Chlorinated Pesticides in Two Connected Himalayan Lakes

PCBs and organochlorine pesticides were determined in water, sediment and zooplankton of two Himalayan lakes, located at different altitudes and connected to each other in such a way that Superior Lake acts as a sedimentation basin for Inferior Lake. Surficial sediments of both lakes show PCB contamination comparable to lakes of industrialised areas. Biota appear to be the main machanism responsible for micropollutant burial in the sediments of Inferior Lake, whereas inorganic particles are more relevant in Superior Lake. Physical and chemical properties of individual chemicals, particularly Henry's law constant and K_ow values, seem to regulate distribution in different environmental compartments.     

Sensitivity of organic contaminant transport and persistence models to Henry's Law constants: Case of polychlorinated biphenyls

Volatilization can be an important process influencing the transport and persistence of trace organic compounds in the environment. Henry's Law constants (H) describe the equilibrium distribution between vapor and aqueous phases, and thus are important for prediction of biogeochemical dynamics of organic chemicals subject to significant volatilization. Variability in reported H values can be appreciable, particularly for compounds such as polychlorinated biphenyls (PCBs) which possess low vapor pressures and solubilities. Recently reported Henry's constants for a number of PCB congeners were compiled to assess the magnitude of this variability. Coefficients of variation were generally 30 to 70% and tended to increase with increasing chlorine substitution and decreasing magnitude of Henry's constant. The influence of this variability on predicted transport and persistence of PCBs in soil and aquatic systems was evaluated using the behavior assessment and two-layer models, respectively. The 2,4′, 2,2′, 5,5′, and 2,2′,4,4′,5,5′ congeners were selected for this analysis on the basis of their high content in Arochlor fluids and range in hydrophobicity, solubility, and reported H values. Results from the two-layer model indicate that both the liquid and gas boundary layers contribute to the overall resistance to mass transfer. Selection of H had a moderate influence on predicted transport and persistence for the idealized lotic aquatic system modeled. Decreasing H and increasing relative contributions of gas phase resistance to overall resistance to mass transport resulted in longer predicted congener persistence. Selection of H also influenced predicted volatilization rates from soil. The volatilization flux rate was found to be controlled by impedance in the soil body for all but very short times, where boundary layer effects tended to limit volatilization. Evaporation, previously demonstrated to enhance volatilization for some chemicals, did not have a significant effect on predicted PCB vapor losses from soil.     

THE TIMES REQUIRED FOR THE ATTAINMENT OF AIR-WATER EQUILIBRIUM IN CLAY SOILS

The coefficient of diffusion of air through the pore water of clay soils has been measured directly and has been shown to be markedly less than for free water and to decrease with water content. It has been shown that these low coefficients of diffusion are not accounted for by the sinuosity of the flow channels, or by any important departure from Henry's law of solution at curved air-water interfaces. The main factors appear to be constrictions in the flow channels and the reduced viscosity of the adsorbed water. It is concluded that air-water equilibrium in partly saturated soils will be attained much more slowly than is generally assumed.     

Procedures for estimating atmospheric deposition properties of organic chemicals

A rationale for procedures to estimate the climatological mean dry deposition velocity and precipitation scavenging ratio of organic chemicals is developed. Both deposition parameters depend strongly on vapor pressure, as it affects the partitioning between vapor and sorbed phases. Separate formulae are presented for vapor and sorbed fractions using their mass-weighted average to describe the deposition parameters for the total airborne concentration. Deposition of sorbed fractions is controlled solely by particle size, and methods for estimating the particle size are presented. Dry deposition velocity for the vapor fraction is derived by semiempirical analysis, and is found to depend on Henry's Law constant, molecular diffusion coefficients in air and water, and the chemical's reaction rate in water. Estimates of the dry deposition velocity for 5 chlorinated hydrocarbons are made and compared with observations. Estimates of the precipitation scavenging ratio are compared with observational data for 11 chlorinated or aromatic hydrocarbons. The estimates generally are within an order of magnitude of the measured values.     

Adjusted Fick's law for gas diffusion in soils contaminated with petroleum hydrocarbons

In bioremediation, hydrocarbon biodegradation rates can be estimated from measured O₂ and CO₂ profiles in situ. Although Fick's law is typically used in calculating the respiration rates, its theoretical base is weak. We propose an adjusted Fick's law with a correction term for the advective flux. We evaluated the applicability of this model to simulate gas diffusion associated with passive degradation of petroleum hydrocarbons in a biopile by comparing the results of this model with the results of Fick's law and the Stefan–Maxwell equations. The deviations from the use of Fick's law depended strongly on the consumption rate of oxygen, the respiration quotient, the mineralization quotient and the volatility of the hydrocarbon. In the whole range of calculated CO₂ concentration versus depth profiles, production rates of CO₂ could be estimated by Fick's law with a maximum deviation of 6%. For the consumption rate of O₂ the maximum deviation is 19%. However, when we used the adjusted Fick's law, the deviations from the results obtained with the Stefan–Maxwell equations were much smaller. The deviations amounted up to only 4%, when the respiration rate r was 1.5 or a hydrocarbon with volatility similar to benzene was present. If the presence of a hydrocarbon was neglected in the calculations, the deviations of the adjusted Fick's law from the results obtained with the Stefan–Maxwell equations were substantial for a hydrocarbon with volatility similar to benzene or toluene.     

REAL-TIME MEASUREMENT AND INTERPRETATION OF THE CONDUCTIVITY AND pH OF PRECIPITATION SAMPLES

A microprocessor-based acid rain monitor was used to make real-time measurements of conductivity and pH of rainwater within individual storms. The automated measurements were compared with laboratory analyses of a subset of the samples taken. The laboratory measurements tended to overestimate the pH because of temperature induced changes in dissociation and Henry's Law constants affecting ionic compounds in the rainwater. The measurement artefact due to these effects may result in average hydrogen ion concentrations being underestimated by approximately 10 to 15% at UK sites. The greatest systematic discrepancies would be anticipated at highly polluted sites and during low temperature acidic episodes. The concept of a rainwater acid fraction was investigated and found to be useful fro quality control and interpretative purposes. The field measurement of conductivity of low ionic strength samples was slightly lower than the corresponding laboratory measurement, possibly caused by limited resolutio nof the conductivity probe or dissolution of fine particulate material.     

Field analysis of mercury in water,sediment and soil using static headspace analysis

We developed a field screening method for the rapid analysis of mercury (Hg) in water, soil and sediment which can be applied cost-effectively at Hg-contaminated sites. The samples are chemically pretreated in ordinary containers, followed by analysis of the sample headspace Hg vapor using a portable commercially-available analyzer. Mercury in water samples is reduced directly by the addition of stannous chloride, while solids are first digested with aqua regia or piranha solution to liberate the Hg from the solids. Aided by vigorous agitation after addition of the reductant, the elemental Hg partitions between the solution and headspace according to Henry's Law. The method requires about 2 and 15 minutes to complete for water and solids, respectively. The method provides very useful detection limits for water (0.1μg/L) and solids (≤ 2μg/g). Intercomparisons with laboratory-analyzed environmental samples have shown reasonable agreement.     

The Henry's Law Constant of Trichloroacetic Acid

The Henry's law constant of trichloroacetic acid [K′_H (mol kg^-1 atm^-1) for the equilibrium CCl₃COOH_(g) ? CCl₃COOH_(aq)] has been determined from measured partial pressures over aqueous solutions at 298.15 K and 308.15 K. Its value is given by: ln(K′_H) = (11.21 ± 0.5) – 8.66 × 10³ (l/T_r – l/T) where T (K) is temperature and T_r is equal to 298.15 K, for an aqueous phase dissociation constant (K_a) of 0.55 mol kg^-1 determined from literature osmotic coefficient and electromotive force data. Accuracy is estimated to be 4–30% in the product K′_HK_a. Trichloroacetic acid is highly soluble and will partition strongly into aqueous atmospheric aerosols, and completely into fog and cloud water. Its occurrence and transport in the environment are therefore to be associated primarily with liquid phases.     

膜下滴灌间作盐生植物棉田水盐运移特征及脱盐效果

盐生植物改良盐碱地作为改良盐碱地最有效的方法之一,具有成本低,效率高,环境友好等特点,有良好的应用前景。该文包括2个研究目标:1)研究间作不同盐生植物的膜下滴灌棉田水盐运移特性;2)研究不同地下水埋深条件下盐生植物的盐碱地改良效果。针对第1个研究目标,设置了3种(孜然、碱蓬、苜蓿)间作盐生植物,进行大田试验,分析地下水埋深相似条件下间作不同盐生植物时土壤水盐分布状况;针对第2个研究目标,设置了4种地下水埋深(1.5、2.0、2.5、3.0 m),进行均衡场试验,研究不同地下水埋深条件下间作盐生植物时地下水的补给比例和土壤脱盐效果。结果表明:1)膜下滴灌棉田间作盐生植物能明显提高棉花生育期膜间和膜内0~30 cm土层平均含水率,且碱蓬效果最明显;间作条件下苜蓿、碱蓬、孜然、对照0~100 cm土层平均脱盐率依次为55.97%、-18.77%、-21.43%、-307.52%,即苜蓿的总脱盐率效果最好;间作盐生植物能在一定程度上抑制0~100 cm土层钠离子和氯离子的聚集,同时增加棉花产量和提高其水分利用效率,且碱蓬对抑制盐离子累积的效果最好;2)间作条件下,地下水埋深越浅,0~100 cm土层平均含水率越高,膜内膜间的含水率差异越小,土壤的脱盐率越低。与未间作相比,间作种植有效的提高了土壤脱盐率,增加了棉花产量、提高了地下水补给比例和水分利用效率。可见,膜下滴灌棉田间作盐生植物不仅可以有效降低土壤含盐量,增加其含水率,还可以增加棉花产量和提高其水分利用效率,且间作碱蓬和苜蓿的节水、脱盐、增产效果较好,这为膜下滴灌土壤盐碱地改良提供了有效的理论支撑。     

Effects of soil erosion on long-term soil productivity in the black soil region of northeastern China

China's northeastern Black Soil Region, one of the country's most important crop production areas, has been seriously affected by soil erosion. This study evaluated the effects of soil erosion on the long-term productivity of this region. We used a modified productivity index (MPI) model (MPI is a number between 0 and 1, with 1 indicating highest productivity) to assess the current effects of soil erosion on soil productivity, as well as to predict long-term change in productivity. Samples from 21 black soil profiles yielded varying MPI values, although most MPI values were indicative of moderate productivity. Organic matter content and available water capacity impact MPI values in the region, whereas soil clay content and pH were less important. Overall, organic matter content and available water capacity of soil profiles decreased consistently as depth of erosion increased. Modeling indicated that MPI in the region will decrease by 0.0052 for each centimeter of topsoil eroded; this rate represents 1% of the current average MPI for the study area. The model predicts a 9.6% productivity reduction over 100 years and a 48.3% reduction over 500 years.     

Stability Studies of Waste Produced in Pilot-Plant Testing using Ferrous-EDTA and Magnesium-Enhanced Lime for Combined Sulfur-Dioxide/Nitrogen Oxides Removal

A pilot-plant-scale study of combined sulfur dioxide/nitrogen oxides (SO₂/NO_x) removal has been performed by the Dravo Lime Company at the Cincinnati Gas and Electric Company's Miami Fort Station in North Bend, Ohio. This study used Dravo's patented Thiosorbic® lime process along with Argonne National Laboratory's (ANL's) patented process for combined SO₂/NO_x removal using the chelate ferrous·ethylenediaminetetraacetate (Fe·EDTA). For approximately nine months, scrubbing tests were carried out, and waste samples were collected. Waste testing at ANL involved two types of long-term chemical stability experiments. In one test, the gas-phase composition above several different samples was studied by mass spectrometry over 22 months. Unexpectedly, production of carbon dioxide and hydrogen sulfide was observed in some of the samples. The other experiment involved solid-phase leaching. Samples were stored for up to 14 months before leaching. Each leachate was tested for total Kjeldahl nitrogen and for the nitrogen-containing ions nitrite, nitrate, and ammonium. Significant amounts of ammonium ions were found in two of the samples. Total leachable nitrogen was found to stabilize after about the first 7 months of storage.     

Silicone rubber sampler to measure dissolved gases in saturated soils and waters

Dissolved gases in saturated soils and waters are usually monitored by the gas extraction equilibration technique (EET). A novel sampling technique, using silicone tubing, was developed and tested with dissolved nitrous oxide (N₂O) and carbon dioxide (CO₂). The device consists of a silicone cell encased in a PVC pipe through which a continuous flow of water was maintained. Dissolved gases diffuse through the silicone membrane into the cell. Air samples were withdrawn from the silicone cell headspace, and gas phase concentrations were converted into dissolved N₂O and CO₂ using Henry's law coefficients. Effluent from the PVC pipe was also collected into evacuated bottles, and dissolved gases content was determined using EET. Statistical analysis showed no significant difference between the two techniques. Regression analysis between concentrations of dissolved N₂O and CO₂ obtained using the new method (Y) and EET (X) yielded the following relationships: Y=0.961 X (R²=0.996) and Y=1.01 X (R²=0.756) for N₂O and CO₂, respectively. Equilibration time between gas and liquid phases across the silicone membrane varies with gaseous species, membrane thickness, temperature, and the silicone cell dimensions (volume to area ratio). After nearly 1 year of operation, no indication of microbial growth on the membrane was found. These results confirm the development of a new, accurate and versatile technique to monitor dissolved gases.     

Sorption and desorption of Zn on Ca-Kaolinite

Experiments on Zn²⁺ sorption-desorption by Ca-kaolinite using a wide range of Zn²⁺ concentrations and two acid pH values allowed us to reach the following conclusions: (1) For Zn²⁺ surface coverages below the kaolinite C.E.C., Zn²⁺ was sorbed mainly via ion exchange; (2) At Zn^2? sorption values above the C.E.C., Zn²⁺ was sorbed with higher affinity by a mechanism stronger than ion exchange, involving a strong association of Zn ions with silicate solid phases; and (3) Use of C.E.C. values and/or Langmuir's calculated maxima would greatly underestimate Zn²⁺ sorption capacity by kaolinite, even at acid pH values.     

不同根系含量对山原红壤抗剪强度的影响

[目的]探讨云南省昆明市呈贡区段家营一植被覆盖的斜坡区不同含量植被根系对山原土壤抗剪强度的增强效应,为相关研究提供理论依据。[方法]制备0(无根系空白样),0.467,0.93,1.4 mg/cm~3这4种根系含量以及20%,25%,30%,35%,40%这5种含水量的根—土复合体试验样品进行抗剪强度试验。[结果]根—土复合体中,植被根系能提供给土壤额外的抗剪能力和抵抗土体变形来增强土体的抗剪强度,植被根系对土体抗剪强度有明显的增强效应,但这种增强效应是有限的。根系含量在0.93 mg/cm~3时,根系对土体的抗剪强度增强效果最好。随着根系含量的增加,黏聚力和内摩擦角总是呈现负相关性的关系,在低含水量情况下,黏聚力随根系含量增加而先降低后增加,内摩擦角随根系含量变化则相反。当含水量低且根系含量相对较少时(当含水量≤35%,根系含量≤0.93 mg/cm~3时),土壤参与剪切整个过程且为被剪主体,得到的黏聚力和内摩擦角均为正值,符合库仑定律;当含水量较高且根系含量较多时(当含水量=35%,根系含量=1.4 mg/cm~3时以及当含水量=45%,根系含量≥0.467 mg/cm~3时),被剪主体为根系,得到的黏聚力为负值,不符合库仑定律。[结论]库仑定律不适用于高含水量和高含量植被根系的根—土复合体抗剪强度的研究。在采用植被护坡时可用试验确定边坡土壤抗剪强度最高时的最佳含根量和含水量。     

Transport of volatile chlorinated hydrocarbons in unsaturated aggregated media

Transport of volatile hydrocarbons in soils is largely controlled by interactions of vapours with the liquid and solid phase. Sorption on solids of gaseous or dissolved compounds may be important. Since the contact time between a chemical and a specific sorption site can be rather short, kinetic or mass-transfer resistance effects may be relevant. An existing mathematical model describing advection and diffusion in the gas phase and diffusional transport from the gaseous phase into an intra-aggregate water phase is modified to include linear kinetic sorption on gas-solid and water-solid interfaces. The model accounts for kinetic mass transfer between all three phases in a soil. The solution of the Laplace-transformed equations is inverted numerically. We performed transient column experiments with 1,1,2-Trichloroethane, Trichloroethylene, and Tetrachloroethylene using air-dry solid and water-saturated porous glass beads. The breakthrough curves were calculated based on independently estimated parameters. The model calculations agree well with experimental data. The different transport behaviour of the three compounds in our system primarily depends on Henry's constants.     

基于Horn-Schunck光流法的多目标反刍奶牛嘴部自动监测

奶牛反刍行为的智能监测对于奶牛健康及提升现代养殖业的水平具有重要意义。奶牛嘴部区域的自动检测是奶牛反刍行为智能监测的关键,该文提出一种基于Horn-Schunck光流法的多目标奶牛嘴部区域自动检测方法。利用Horn-Schunck光流法模型求取奶牛反刍视频中各时间序列图像的光流场,将各帧序列图像中运动较大的光流数据进行叠加,获取奶牛反刍时的候选嘴部区域,最后运用奶牛嘴部区域检测模型实现反刍奶牛嘴部区域的检测。为了验证算法的有效性,利用不同环境下获取的12段视频进行验证,选取的12段视频的每段时长10 s,每段视频帧数在250~280帧之间,结果表明,对于多目标奶牛,12段视频中有8段视频可以成功检测到反刍奶牛的嘴部区域;根据所定义的真实充盈率指标与检测充盈率指标,分别统计了8段成功检测反刍奶牛嘴部区域的视频检测结果,试验表明,8段视频中最大真实充盈率为96.76%,最小真实充盈率为25.36%,总体平均真实充盈率为63.91%;最大检测充盈率为98.51%,最小检测充盈率为43.80%,总体平均检测充盈率为70.06%。研究结果表明,将Horn-Schunck光流法应用于多目标奶牛嘴部区域的自动检测是可行的,该研究可为奶牛反刍行为的智能监测提供参考。     

Spatial organization of soil nematode communities in urban landscapes: Taylor's Power Law reveals life strategy characteristics

It is well known that Taylor's power law describes spatial aggregation, but its ecological interpretation remains elusive. Here we used data on spatial organization of soil nematode communities in urban landscapes to test relationships between nematode life history characteristics and the power law aggregation indicator, b. Forty seven genera of soil inhabiting nematodes were identified from 360 samples taken from turfgrass lawns at three public schools located in each of three northeast Ohio cities in July and October 2007. The nematodes were classified according to their life-styles in three life history classifications: trophic group, colonizer-persistor (cp) class, and functional guild, a combination of trophic group and cp-class. Estimates of Taylor's b for 28 more common genera ranged from 1.21 to 2.34. Estimates of b for trophic group, cp-class and functional guild ranged from 1.41 to 2.10, 1.34 to 1.97 and 1.41 to 2.39, respectively. Segregating genera by their trophic group, cp-class and functional guild each accounted for as much inter-genus variation in Taylor's power law as fitting 28 separate regressions. The improvements of fit in parallel line analyses for the three life-style categories over 28 lines for individual genera were highly significant. Bacterial- and plant-feeding groups were more highly aggregated than omnivorous and predatory nematodes. Nematodes in cp-classes 1 and 2 tended to be more aggregated than those in higher cp-classes. The functional guilds were generally more highly aggregated than individual genera, suggesting a higher degree of aggregation at the functional guild level. We conclude that nematode genera vary in their spatial organizations, but membership in a cp-class and functional guild accounts for much of this variability. Thus, Taylor's power law aggregation indicator, b, is sensitive to nematode feeding habits and life strategy traits as they influence a population's pattern of spatial organization.     

The contribution of physics to land drainage

The physics of land drainage is developed from the application of Darey's law to the water movement produced as a result of the conditions at the boundaries of the groundwater region in a given drainage situation. The physical understanding of the groundwater problem so obtained allows land drainage to be considered as an engineering operation founded on rational scientific principles and allows recommendations to be made concerning the design of installations. However, for theory to be applied in many field situations, a greater understanding of the soil-water physics of heterogeneous soils, of fissured soils and of swelling soils is required.