Measured Concentration Levels Research Articles

Dispersion processes in reservoirs and natural streams

The application of dispersion models in estimating the concentration levels of a solute, or a pollutant constituent, resulting from discharging waste into reservoirs and natural streams is presented. For the reservoir case, the mass balance principle of the aggregated dead zone (ADZ) model is employed, from which a general formulation for the dispersion of a pollutant constituent is derived. A hypothetical case is presented where an accidental spillage of a chemical discharge into a reservoir is considered. The prediction of the transient change in the concentration levels is analytically derived for the general case of reservoirs of arbitrary volumes and of various influx rates and duration. For the case of natural streams, the classic version of the Fickian diffusion model is modified, from which an expression for quantifying the coefficient of dispersion is proposed. The proposed dispersion model has been applied to a case study carried out on Waikato River, in New Zealand, where a dye is released in the river for the purpose of providing information about flushing rates at low steady flows. It has been demonstrated that the proposed dispersion model gives a more realistic estimation of the concentration profiles than those obtained from other existing models. Reasonably good comparisons were obtained with the measured concentration levels in the river at both the near-field and the far-field locations from the injection site.

Concentração de flúor em diferentes espécies de pastagens da região carboelétrica de Candiota, RS.

Estudos anteriores demonstraram uma considerável contaminação de pastagens da região carboelétrica de Candiota, RS. Neste trabalho 21 espécies de pastagens nativas desta região foram identificadas e analisadas quanto a seus teores de flúor. A determinação deste elemento foi feita por meio da técnica de eletrodo íon-seletivo em soluções resultantes da decomposição de amostras de pastagens com mistura HNO3 + H2O2. Amostras coletadas em três pontos das vizinhanças da usina termoelétrica (UTM) acusaram valores de referência. A diferenciada capacidade de absorção e de retenção deste elemento pelas espécies estudadas fica evidenciada pela variabilidade dos níveis de concentração medidos.

Spatial and temporal distributions of 1,3-dichloropropene in soil under drip and shank application and implications for pest control efficacy using concentration-time index

A field experiment was conducted to study the spatial and temporal distributions of (EZ)-1,3-dichloropropene (1,3-D) in the soil and effects on pest control efficacy. An emulsifiable concentrate formulation of 1,3-D (Telone EC) was applied with drip irrigation at 47 kg AI ha−1 to two different depths (2.5 and 20.3 cm, respectively). Comparisons were made between the two drip treatments and a direct shank injection of 1,3-D (Telone II) at 112 kg AI ha−1. Concentrations of 1,3-D in soil air were measured at several locations over time to determine the spatial and temporal characteristics, and to calculate the concentration–time index (CT). Citrus nematodes (Tylenchulus semipenetrans) were placed in the fumigated soil at 25 cm depth and their mortality rates were compared to the calculated CT. Distributions of 1,3-D were found to be relatively uniform in both the drip irrigation and the shank injection treatment. An application rate of 47 kg ha−1 with drip irrigation was sufficient to achieve significant concentration levels in soil beds. Applying 1,3-D with direct shank injection at 112 kg ha−1 extended the measurable concentration levels to the furrows between the soil beds and to a depth of 1 m below the soil surface. Effective control of T. semipenetrans was achieved with both the drip irrigation and the shank injection. A threshold soil 1,3-D CT value of 12 μg h cm−3 was needed to reach a 100% efficacy for T. semipenetrans. The study indicates that 1,3-D fumigation may be carried out with drip irrigation at very low rate, and a CT index may be derived to aid in the determination of a minimum effective dosage. © 1999 Society of Chemical Industry

Spatial and temporal distributions of 1,3-dichloropropene in soil under drip and shank application and implications for pest control efficacy using concentration-time index

A field experiment was conducted to study the spatial and temporal distributions of (EZ)-1,3-dichloropropene (1,3-D) in the soil and effects on pest control efficacy. An emulsifiable concentrate formulation of 1,3-D (Telone EC) was applied with drip irrigation at 47 kg AI ha -1 to two different depths (2.5 and 20.3 cm, respectively). Comparisons were made between the two drip treatments and a direct shank injection of 1,3-D (Telone II) at 112 kg AI ha -1 . Concentrations of 1,3-D in soil air were measured at several locations over time to determine the spatial and temporal characteristics, and to calculate the concentration-time index (CT). Citrus nematodes (Tylenchulus semipenetrans) were placed in the fumigated soil at 25 cm depth and their mortality rates were compared to the calculated CT. Distributions of 1,3-D were found to be relatively uniform in both the drip irrigation and the shank injection treatment. An application rate of 47 kg ha -1 with drip irrigation was sufficient to achieve significant concentration levels in soil beds. Applying 1,3-D with direct shank injection at 112 kg ha -1 extended the measurable concentration levels to the furrows between the soil beds and to a depth of 1 m below the soil surface. Effective control of T. semipenetrans was achieved with both the drip irrigation and the shank injection. A threshold soil 1,3-D CT value of 12 μg h cm -3 was needed to reach a 100% efficacy for T. semipenetrans. The study indicates that 1,3-D fumigation may be carried out with drip irrigation at very low rate, and a CT index may be derived to aid in the determination of a minimum effective dosage.

Application of a Three-Layer Photochemical Box Model in an Athens Street Canyon

ABSTRACT The aim of this paper is to show that a photochemical box model could describe the air pollution diurnal profiles within a typical street canyon in the city of Athens. As sophisticated three-dimensional dispersion models are computationally expensive and they cannot serve to simulate pollution levels in the scale of an urban street canyon, a suitably modified three-layer photochemical box model was applied. A street canyon of Athens with heavy traffic was chosen to apply the aforementioned model. The model was used to calculate pollutant concentrations during two days with meteorological conditions favoring pollutant accumulation. Road traffic emissions were calculated based on existing traffic load measurements. Meteorological data, as well as various pollutant concentrations, in order to compare with the model results, were provided by available measurements. The calculated concentrations were found to be in good agreement with measured concentration levels and show that, when traffic load and traffic composition data are available, this model can be used to predict pollution episodes. It is noteworthy that high concentrations persisted, even after additional traffic restriction measures were taken on the second day because of the high pollution levels.

Field testing of new aerosol sampling method with a porous curved surface as inlet.

A new aerosol sampling method, utilizing a porous curved surface as the sampling inlet, has recently been developed. Previous laboratory evaluations of this method have demonstrated its important features, such as low wind sensitivity and good filter collection uniformity. In this study a prototype incorporating the new method was evaluated in the field as a stationary and personal sampling device. The small sampler, utilizing a 25-mm filter is called the button aerosol sampler and was evaluated for collecting total airborne dust and fungal spores. The study was performed in nine poorly maintained inner-city houses during environmental cleanups at different cleanliness levels. The button sampler was used in parallel with the standard 37-mm closed-face filter cassette. Four collocated samplers of each type were tested at all sites as stationary samplers, and three samplers of each type were tested at two sites as personal samplers. Aerosol samples were collected on filters and analyzed using the gravimetric method for total dust and epifluorescence microscopy for fungal spores. The average particle concentration values measured with the button sampler and with the standard sampling cassette were found to correlate well within ranges of 10(1)-10(3) micrograms/m3 for total dust and 10(3)-10(5) spores/m3 for airborne fungi. The measurement results obtained with the new button sampler showed lower intersample variations of the measured concentration levels and higher uniformity of the particle deposits on the filters than those obtained with the standard cassette.

Preconcentration and matrix separation of precious metals in geological and related materials using metalfix-chelamine resin prior to inductively coupled plasma mass spectrometry

A method for determining Au, Pt, Pd, Ir and Rh in ores and silicates and Fe-formation rocks is described. Sample decomposition was carried out with aqua regia and HF, followed by fusion of any insoluble residue with Na 22O 2 in a glassycarbon crucible. The precious metals were separated, in 1.2 mol dm −3 HCl media, from the matrix elements by ion-exchange, using a mini-column with tetraethylenepentamine (metalfix-chelamine) resin. The resin was destroyed with HNO 3 and H 2O 2 in a high-pressure vessel assisted by microwave heating, and the precious elements were determined by flow-injection inductively coupled plasma mass spectrometry. The sample treatment, optimization of analytical variables and measurable concentration levels are discussed. The limits of quantification (10 sd n − 1 ) calculated from a procedural blank sample solution were 4.0, 2.0, 1.5, 0.8 and 0.5 ng g −1 for Au, Pt, Pd, Ir and Rh, respectively. The accuracy of the proposed method was tested by determining these elements in SARM 7 platinum-ore reference material. For all the analytes, the relative standard deviation of the combined dissolution, separation and determination methods was below 3.5% ( n = 6).

On-line ion-exchange separation and determination of niobium, tantalum, tungsten, zirconium and hafnium in high-purity iron by flow injection inductively coupled plasma mass spectrometry

A study was made to investigate the feasibility of using an anion-exchange resin for on-line separation of trace amounts of niobium, tantalum, tungsten, zirconium and hafnium from iron matrix samples. The incorporation of a micro-column packed with Dowex 1X8-100 ion-exchange resin into a flow injection system is presented. The detection was done with inductively coupled plasma mass spectrometry (ICP-MS). The sample treatment, optimization of analytical variables and measurable concentration levels are discussed. Recoveries from standard additions to a high-purity iron were for all the analytes close to 100%, with relative standard deviations ranging from 0.7 to 3.0%. The limits of quantification (10 s n−1 ) calculated from a 5% (m/v) iron sample solution were 8, 5, 14, 12 and 10 ng g −1 for Nb, Ta, W, Zr and Hf, respectively. The accuracy of the proposed method was tested by determining these elements in Euronorm-CRM 098-1 reference material. Recoveries from 0.250 g test portions of the above reference material spiked with 2.5 and with 12.5 ng each of the five analytes are reported.

Concentration in local television markets

This article asserts that the degree of economic concentration in markets is affected by the precise definition of the markets and that measurement is problematic because media firms operate in a number of markets and face competition from substitutes. The author builds several alternative market definitions for local television and shows that there are significant differences in the measured concentration levels using the market definitions.

Continuous Analysis of Vehicle Exhaust Gas by Fourier-Transform Infrared Spectroscopy

Fourier-transform infrared spectroscopy (FT-IR) was applied to a continuous measurement of unregulated emissions from a diesel engine. Improvements in measuring the diesel exhaust gas were achieved by heating the gas sampling Une, adapting the filter to remove particles in the exhaust gas, and modifying the window material of the sampling cell. An increase in the sample flow rate as well as a volume reduction of the sampling cell could improve the response of FT-IR, though it was insufficient under transient conditions. It was confirmed that FT-IR could continuously and simultaneously detect unregulated emissions, such as HCHO and NHi, as well as regulated emissions. The measured concentration level of unregulated emissions was very low. It was suggested that FT-IR might be useful in estimating any change in the combustion process by measuring the intermediate products, including HCN and HONO, which are related to NO production during combustion. It was also demonstrated that gaseous unregulated emissions from vehicles can be measured in real-time by FT-IR.

Pharmacokinetics of omega-3-fatty acids during ingestion of fish oil preparations

An in vivo comparison of three dosages (3 g, 6 g, 12 g) of two different fish oil preparations in terms of plasma concentrations of their major active components eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) was performed. The plasma accumulation was measured during 28 days of ingestion and an equally long wash out period. Data were scrutinized for bioavailability in order to distinguish between the efficiency of the two preparations. Rapid increases in EPA and DHA plasma concentrations can be demonstrated at all dosages during a 28-day ingestion period. EPA accumulated more during ingestion of high than of low dosages of fish oil. DHA revealed almost identical increases and peak values in plasma concentrations in all subgroups. The present data demonstrate dose dependent increases of EPA concentrations whereas DHA plasma concentrations are comparable in all dosages investigated. Measurable EPA and DHA plasma concentration levels are inappropiate means to explain clinical effectiveness. These results were found in both commercially available fish oil preparations. Direct comparison of both preparations revealed no differences in bioavailability.

Determination of cobalt at low levels in silicate rocks by atomic absorption spectrometry using a continuous on-line precipitation-dissolution procedure based on 1-nitroso-2-naphthol

A continuous pre-concentration flame atomisation atomic absorption spectrometric method for the determination of cobalt by precipitation with 1-nitroso-2-naphthol is proposed. The sample treatment, dissolution of the tris(1-nitroso-2-naphthalato)cobalt(III), optimisation of analytical variables and measurable concentration levels are discussed. Several calibration graphs were used for the determination of CoII in the range 1–180 ng ml–1 with a sampling frequency of between 4 and 40 h–1 and a relative standard deviation of between 2.5 and 3.0%. The proposed method was successfully applied to the determination of Co at the µg g–1 level in silicate rocks.

Inductively coupled plasma atomic emission spectrometric determination of arsenic, antimony, tin, bismuth, selenium and tellurium in leads and refined coppers

Methods were developed for the determination of As, Sb, Sn, Bi, Se and Te in leads and refined coppers using both direct sample solutions and the hydride generation technique. For hydride generation in coppers, prior separation of the matrix was necessary owing to the inhibiting effect of copper on hydride formation. For leads, it is possible to generate hydrides for As, Sb, Bi and Se directly from test solutions. Tin and Te require prior separation of the matrix in order to avoid lead precipitation in the hydrochloric medium suitable for the generation of the tin hydride in the former instance and the inhibition produced by lead in the latter. The dissolution of samples, separation processes, sample treatment, choice of analytical lines and measurable concentration levels were investigated.

Correlation of studies of surface-level carbon monoxide concentrations and sodar-observed thermal structures

Measured concentration levels of carbon monoxide present in the atmosphere near the ground surface have been studied in relation to atmospheric stability inferred from acoustic sounder vis-à-vis the density of motor-vehicular traffic responsible for the emission of carbon monoxide gas. It has been seen that concentration levels of carbon monoxide during peak traffic hours depend on the prevailing stability of the atmosphere. The need for continuous monitoring of atmospheric stability at a place using acoustic sounder to assess air quality has been emphasized.

A human exposure assessment study using personal monitoring of carbon monoxide—direct and indirect methods

Data obtained from fixed site monitors have been used and were considered adequate to estimate the populations exposure to pollutants. Thus, residential exposure was based on the likely occurrence of a pollutant when residential demographic data were merged with pollutant concentrations observed at the nearest fixed site. The recent development of personal exposure monitors (PEMs) have made available the opportunity to measure a person's total exposure in both the ambient and indoor air. This paper introduces two approaches to determine exposure and describes experimental data obtained during application of these approaches to a pollutant, carbon monoxide. One is the direct approach in which a representative sample of the population is selected and sampling is conducted using a PEM. The indirect approach is the combination of collected field data from activity patterns and measured concentration levels within microenvironments. The conclusions combine statistical survey design techniques and PEM concentration data to produce an exposure profile for a representative population.

The identification of runoff sources of a forested lowland catchment: A chemical and statistical approach

The seasonal and intra-storm variations in streamwater chemistry are described and used to distinguish runoff and solute sources in the catchment, e.g. throughfall as channel precipitation, litter-layer water and water from the organic rich topsoil, throughflow in the sandy A2 horizon. Statistical treatment of the streamwater concentration data by means of factor and cluster analysis show the significant relationships and different behaviour of three groups of solute species: K, NH 4, NO 3 Mg , Na, Cl/Ca, Si, SO 4, each group having a different response to rainfall. Three types of storm events with specific hydrologic situations could be distinguished: (1) winter and spring storms generating direct runoff and baseflow; (2) summer and autumn storms generating only direct runoff; and (3) snowmelt runoff. Each of these types of runoff event is characterized by a particular solute behaviour, related to contributions from the different runoff and solute sources. The validity of this model of solute contributions by these sources (throughfall (stemflow), litter and soil waters) is corroborated by the measured concentration levels of these sources.

Aircraft sampling of the sulfate layer near the tropopause following the eruption of Mount St. Helens

Twenty‐three filter sampling flights of the NASA Lewis F‐106 aircraft, were conducted in the Great Lakes region between June 4 and December 23, 1980, following the major eruption of Mount St. Helens (Washington State) on May 18. The IPC‐1478 filters were exposed over an altitude range spanning the local tropopause. A filter sample exposed above the tropopause on June 5 indicated a sulfate level of 50 times the baseline measurements, which is consistent with the trajectory predictions of the leading edge of the cloud on its second transit around the earth. Subsequent measurements over a period of 7 months revealed the existence of a layer of sulfate above the tropopause that decayed to a level of about 4 times previously measured background levels by the beginning of August. Concentration of nitrate above the tropopause exhibited considerable variability and showed some enhancement compared with previously measured concentration levels. On the basis of the null results of X ray fluorescence measurements, there is no evidence of ash particle concentrations >3.4 μm/m3 persisting in the layer above the tropopause following the second transit of the cloud.