A New Tape Reagent for the Determination of Hydrogen Sulfide in Air

The lead acetate paper tape reagent method for the estimation of hydrogen sulfide in air has been reviewed with the conclusions that the colored spots on which the quantitative estimation is based are not stable and do not lend by themselves to accurate results. Although it may be retained for grab sampling work, the lead acetate paper tape reagent is not acceptable as a stoichiometric reagent in any case where long duration sampling periods are concerned like in air pollution studies. A new mercuric chloride paper tape reagent has been developed as a substitute. Due to the fact that the colored spots resulting from the action of hydrogen sulfide on mercuric chloride are sensitive and very stablet, this new paper tape reagent is proposed as an adequate and reliable analytical too for the estimation of hydrogen sulfide in air. Also, a more comprehensive application of the paper tape analytical system is proposed throughout a suitable control of the factor tape retention capacity vs sampling rate which imposes some restrictions in the selection of the practical working range of concentrations. Nevertheless this working range is still wide enough to encompass all the hydrogen sulfide concentrations normally encountered in the city atmosphere.     

Modifications to an H2S Tape Sampler for Increasing Sensitivity and Accuracy in H2S Sampling

The tape samplers using lead acetate impregnated paper tapes for continuous hydrogen sulfide sampling are subject to a number of errors which can throw considerable doubt on the accuracy of H₂S concentrations being measured. Some of the errors have been minimized with a change in the humidification system and a reduction of the lamp intensity in the optical system.     

Comparison of Hydrogen Sulfide Analysis Techniques

A summary and critique of common methods of analysis for H₂S is presented. The procedures described are: reflectance from silver plates and lead acetate-coated tiles, lead acetate and mercuric chloride paper tape, sodium nitroprusside and methylene blue wet chemical methods, infrared spectrophotometry, and gas chromatography. Pertinent details included for each method are type (continuous, semicontinuous, averaging), lower detection limit, range, known interferences and suggestions for their elimination, and appropriate instrument parameters as wavelength, flow rates, temperature, and sample size. The limitations of each technique are clearly described, as are the advantages, in such a manner as to aid the user to select proper instrumentation for his analytical requirements.     

Index

Abstract

Activated carbon (AC) adsorption has long been considered to be a readily available technology for providing protection against exposure to acutely toxic gases. However, ACs without chemical impregnation have proven to be much less efficient than impregnated ACs in terms of gas removal. The impregnated ACs in current use are usually modified with metalloid impregnation agents (ASC-carbons; copper, chromium, or silver) to simultaneously enhance the chemical and physical properties of the ACs in removing specific poisonous gases. These metalloid agents, however, can cause acute poisoning to both humans and the environment, thereby necessitating the search for organic impregnation agents that present a much lower risk. The aim of the study reported here was to assess AC or ASC-carbon impregnated with triethylenediamine (TEDA) in terms of its adsorption capability for simulated hydrogen sulfide (H₂S) and sulfur dioxide (SO₂) gases. The investigation was undergone in a properly designed laboratory-scale and industrial fume hood evaluation. Using the system reported here, we obtained a significant adsorption: the removal capability for H₂S and SO₂ was 375 and 229 mg/g-C, respectively. BET measurements, element analysis, scanning electron microscopy, and energy dispersive spectrometry identified the removal mechanism for TEDA-impregnated AC to be both chemical and physical adsorption. Chemical adsorption and oxidation were the primary means by which TEDA-im pregnated ASC-carbons removed the simulated gases.     

Characterization of the olfactory impact around a wastewater treatment plant: Optimization and validation of a hydrogen sulfide determination procedure based on passive diffusion sampling

A monitoring program based on an indirect method was conducted to assess the approximation of the olfactory impact in several wastewater treatment plants (in the present work, only one is shown). The method uses H₂S passive sampling using Palmes-type diffusion tubes impregnated with silver nitrate and fluorometric analysis employing fluorescein mercuric acetate. The analytical procedure was validated in the exposure chamber. Exposure periods of at least 4 days are recommended. The quantification limit of the procedure is 0.61 ppb for a 5-day sampling, which allows the H₂S immission (ground concentration) level to be measured within its low odor threshold, from 0.5 to 300 ppb. Experimental results suggest an exposure time greater than 4 days, while recovery efficiency of the procedure, 93.0 ± 1.8%, seems not to depend on the amount of H₂S collected by the samplers within their application range. The repeatability, expressed as relative standard deviation, is lower than 7%, which is within the limits normally accepted for this type of sampler. Statistical comparison showed that this procedure and the reference method provide analogous accuracy. The proposed procedure was applied in two experimental campaigns, one intensive and the other extensive, and concentrations within the H₂S low odor threshold were quantified at each sampling point. From these results, it can be concluded that the procedure shows good potential for monitoring the olfactory impact around facilities where H₂S emissions are dominant.

Implications: Passive samplers are very attractive tools to experimentally tackle a number of air pollution problems, especially those related to odor impact. Their small size and cost permit a denser sampling design and thus a more detailed spatial characterization than other techniques. On the other hand, the large inherent variability in passive sampler measures requires an uncertainty analysis of the chemical species and analytical procedures used.     

Performance Characterization and Optimization of the AgNO3-Filter/FMA Fluorimetric Method for Atmospheric H2S Measurements

This sensitive, albeit precarious, method for measuring ppb-ppt (V/V) concentrations of H₂S was examined for various sources of potential error within the procedure. Filter preparation, filter storage, filter extraction, fluorimetric reagent stabilities, matrix differences between standards and samples, and possible interferences from other sulfur-containing compounds were separately studied for their effects on the analytical performance of the method. The overall method showed no Interference from SO₂, CS₂, COS, CH₃SH, CH₃SCH₃, and SO₄ ^-2. To minimize bias and obtain a reliable estimate of precision, the method should be calibrated with H₂S standards rather than liquid bisulfide standards. The measurement precision is a function of the quantity of H₂S collected as Ag₂S and/or AgSH on the impregnated filters. Because of the method’s linear dynamic range, sufficient air should be sampled to achieve filter loadings of 15 to 35 ng S/filter. A quality control method based on fluorescein mercuric acetate (FMA) is presented that ensures data quality while reducing the otherwise frequent need for fluori-metric calibration.     

Instrumenting Light Aircraft for Air Pollution Research

Light aircraft and helicopters have been occasionally used to conduct aerial traverses for a single pollutant or atmospheric tracer. The continuous analyzer or sample collector is temporarily tied down with a seat belt or hand held. Flight variables are visually observed and written on the recorder chart, a notebook or possibly voice-recorded on a portable tape recorder. The versatile airborne instrumentation package described can measure and record up to 27 pollutant and flight variables from a Cessna Skymaster center-line thrust, light twin. Real-time analysis instrumentation include non-dispersive infrared analyzers for CO₂, CO, and hydrocarbons, conductivity and coulometric analyzers for sulfur dioxide and sulfur-containing gases, and Charlson-Ahlquist visual range nephelometer. A Battelle “bulk sampler” is used to collect particulates for weighing and microscopic examination. Indicated air speed, altitude, rate of climb, magnetic heading, temperature, and relative humidity are continuously measured. All variables are sequentially recorded on a 7-track, 200 bit per second, 27-channel, magnetic tape data logging system. Measured variables are recorded once each 0.3 to 0.8 sec—equivalent to 33-100 ft of traversedepending upon the number of variables recorded (i.e., between 9 and 27) when flying at 90 mph. Tape data are reduced directly by IBM 360 computer to a digital print-out or from tape to an X-Y analog plot.     

液电等离子体处理有机废水

水中高压脉冲放电可引起物理和化学效应 ,物理效应形成紫外光和冲击波 ,化学效应主要促使活性物质的形成。利用这一技术处理废水具有高能电子、紫外线、臭氧等多因素的综合作用 ,是集光、电、化学氧化于一体的新型水处理技术 ,可大大增强处理效果。阐述了这一技术在有机废水处理方面的技术原理、电源、反应器类型 ,以及研究现状和发展趋势 ,并对这一技术在废水处理中的应用进行展望     

Insecticide fingerprinting tecinique for detection and location of organochlorine insecticide rssiduss in foods

Abstract

Insecticide fingerprinting technique enables the detection and location of DDT and HCII residues in vegetables through the development of green and Prussian blue colors respectively. Cut vegetables are pressed against o‐tolidine impregnated paper and exposed to sunlight where colored spots appear instantly. The studies on 18 vegetable varieties revealed the pesticide residues and their distribution in different tissues. This direct method is sensitive (0.3 μg for HCII & 0.5 μg for DDT) and has special applications in quality control laboratorios and food industry.     

Impact of Light Duty Diesels on Visibility in California

This paper investigates the impact of light duty diesels on California visibility in the early 1990s. It is found that, without increased dieselization, there will be little change in statewide visibility levels from the late 1970s to the early 1990s. Visibility impacts from diesels are calculated for various scenarios of diesel use and particulate control. The likely dieselization (20%), do nothing particulate control (0.4 g/ml) scenario will change projected statewide emissions slightly for HC ( –2 % ) , NO _x (+1%), SO _x (+5%), and TSP (+1%) but will increase statewide emissions of elemental carbon (soot) by about 80%. Simplistic haze budget calculations indicate that this increase In soot emissions should reduce visibility about 10 to 25% in California. More precise and geographically detailed visibility calculations are performed by applying a lead tracer model to data for 86 California locations. The lead tracer model indicates that the likely dieselization, do nothing control scenario will reduce visibility by about 10 to 35%, with the greatest impacts occurring in and near urban areas. Actual visibility decreases for this scenario may even be much greater, 20 to 50%, because the analysis does not address two other significant factors: (1) increased SO₄ ^–2 levels due to catalytic SO₂ oxidation by soot and to higher SO₂ emissions, and (2) increased soot emissions due to dieselization of the medium and heavy duty fleets.     

Determination of Sulfur Oxides in the Flue Gases of the Pulping Processes

The body of information presented in this paper is directed to the operating personnel and process engineers employed in the power and recovery departments of a chemical pulping operation. The proper evaluation of the total analytical and sampling system (TASS), to be used in the determination of sulfur oxides is as important as a proper analytical and recording system (ARS). The presence of other sulfur gaseous compounds and particulates could greatly influence the results of the determination.

The analytical method employed determines sulfur dioxide and trioxide from an aliquot of the trapping solution, 3% hydrogen peroxide and 8 0% isopropyl alcohol respectively. The aliquot is titrated with barium perchlorate in the presence of Thorin indicator. The results of evaluating the method indicated negligible interference from the presence of hydrogen sulfide, mercaptans and nitrogen oxides. A blank correction of 15 parts per million (ppm) is recommended whenever 100 ppm of hydrogen sulfide or more are simultaneously present in the gas stream. Particulaies are shown to interfere either by addition or subtraction. Sulfate particulates that will add to the determination must be removed, but in doing so, care must be exerted to avoid surface-contacting conditions that promote reaction between carbonates and the sulfur oxides. The integrated method of sampling and analysis will permit determinations from a flue gas with sulfur oxides concentrations of 30 ppm and above. The relative standard deviation improves from 10% at 100 ppm SO₂ to 2.6% at 1000 ppm SO₂. In both cases, sulfides were present.     

Photocatalytic degradation of phenol using Ag core-TiO<Subscript>2</Subscript> shell (Ag@TiO<Subscript>2</Subscript>) nanoparticles under UV light irradiation

Ag@TiO₂ nanoparticles were synthesized by one pot synthesis method with postcalcination. These nanoparticles were tested for their photocatalytic efficacies in degradation of phenol both in free and immobilized forms under UV light irradiation through batch experiments. Ag@TiO₂ nanoparticles were found to be the effective photocatalysts for degradation of phenol. The effects of factors such as pH, initial phenol concentration, and catalyst loading on phenol degradation were evaluated, and these factors were found to influence the process efficiency. The optimum values of these factors were determined to maximize the phenol degradation. The efficacy of the nanoparticles immobilized on cellulose acetate film was inferior to that of free nanoparticles in UV photocatalysis due to light penetration problem and diffusional limitations. The performance of fluidized bed photocatalytic reactor operated under batch with recycle mode was evaluated for UV photocatalysis with immobilized Ag@TiO₂ nanoparticles. In the fluidized bed reactor, the percentage degradation of phenol was found to increase with the increase in catalyst loading.     

CdS-TiO_2/MWCNTs结构表征及其光催化性能

采用溶胶-凝胶法,制备了多壁碳纳米管(MWCNTs)负载的双组分复合半导体光催化剂CdS-TiO2/MWCNTs。通过透射电镜(TEM)、比表面分析(BET)、X射线衍射(XRD)和紫外-可见吸收光谱(UV-vis)等分析方法对光催化剂进行了结构表征,并考察了CdS-TiO2/MWCNTs对甲苯降解的光催化性能。结果表明:纳米活性粒子CdS-TiO2均匀负载于MWCNTs上,比表面积、光吸收阈值和强度增大,活性粒子间以及活性粒子与载体之间具有协同作用,有利于光催化性能的提高,CdS-TiO2/MWCNTs在主波长为254 nm紫外光照射下对甲苯的降解效果较好,去除率可达55.3%。     

A Simple Technique for Measuring Mean H2S Concentration

Lead acetate impregnated ceramic tiles are useful devices for determining H₂S levels in the outdoor air. The exposure of tiles in simple shelters and for an overnight period is effective in an areawide sampling program to determine: (1) whether a significant H₂S source exists, (2) the source location, (3) the area affected, and (4) the relative intensity pattern.

On the basis of an overnight exposure, tiles can “see” a mean H₂S concentration range of 0.003 to 0.3 ppm. The lower level of sensitivity is near 0.03 ppm X hr. Hence, tiles offer a way to verify whether hourly air quality standards are being exceeded.

Tiles can be qualitatively evaluated against: experience, known effects, or by ranking against each other. Tiles can be semi-quantitatively evaluated by visual grading against painted standards developed by exposing tiles of particular manufacture to known H₂S dosages.     

An Inspection Method for Automobile Hydrocarbon Emission

A quick, simple method for identifying and distinguishing lead from other heavy metals in living plants has been developed using sodium rhodizonate (C₆0₆Na₂) which forms a scarlet precipitate with lead at approximately pH 2.8. Hand sections of plant tissues are treated with rhodizonate reagent, buffered, and examined microscopically. Very little time and/or effort is required for this method. Those cells and tissues contaminated with lead turn scarlet—color intensity being directly related to concentration. Lead may be detected in quite low concentrations and, most importantly, may be observed in situ; its entry and movement through the plant can thus be followed. In an area of moderate traffic of Downey, Calif. (Southeast Los Angeles), lead was found abundantly on leaves as well as on and in roots of garden-grown lettuce; origin of this lead is presumed to be from car exhausts.     

Predicting and Managing the Health Risks of Sour-Gas Wells

The development of sour-gas resources in Canada and the United States has prompted concerns about the public health risks of accidental releases of gas contaminated with hydrogen sulfide (H₂S) from wells. This paper focuses on methods for improving the prediction and management of those risks. Data associated with the health effects of hydrogen sulfide are examined, and it is suggested that sublethal effects should be addressed in risk assessments of sour-gas wells along with the life-threatening effects normally considered. The demarcation of hazard zones around wells can be improved by using a statistical approach for estimating an upper-bound H₂S release rate; this rate can then be used in an atmospheric dispersion model to estimate maximum distances to downwind concentrations for lethal (300 ppmv) and sublethal (50 ppmv) effects resulting from an accidental release. A vertical release is found to have little impact, especially under stable atmospheric conditions; horizontal releases, on the other hand, result in the greatest downwind distances for health impacts. Management of health risks depends on a mix of safety technologies and contingency actions, such as well-ignition options and provision for post-release monitoring and assessment of ambient H₂S concentrations.     

Nitrogen Dioxide Absorption and Sulfide Oxidation in Aqueous Sulfide

ABSTRACT

Rates of nitrogen dioxide (NO₂) absorption and sulfide oxidation were measured in a highly characterized stirred cell contactor at 55 °C, with O₂ present in the gas phase. The rate constant of the reaction between NO₂ and sul-fide at 55 °C was determined to be 26.4 x10⁵ M^-1sec^-1. A reaction mechanism was proposed that is consistent with the kinetic data. NO₂ absorption initiates sulfide oxidation in the presence of oxygen. The rate of sulfide oxidation increased with sulfide and oxygen concentration and with the rate of NO₂ absorption. Furthermore, thiosulfate was an effective inhibitor of sulfide oxidation.     

Studies on a New Method of Simultaneously Removing Sulfur Dioxide and Oxides of Nitrogen from Combustion Gases

Simultaneous reduction of SO₂ and NO by catalyzed reaction with carbon monoxide at space rates approaching 10⁴ vol/vol/hr has been shown. The reaction of sulfur dioxide with carbon monoxide results in the formation of carbon dioxide and elemental sulfur. Nitric oxide reacts with carbon monoxide to form carbon dioxide and molecular nitrogen. Metals supported on alumina appear to be the preferred catalysts. Among the effective metals are copper, silver, and palladium. A side reaction of carbon monoxide with elemental sulfur to form carbonyl sulfide requires that the initial amount of carbon monoxide be stoichio-metric for the amount of sulfur dioxide plus nitric oxide present. A furnace employing this method would have to be operated at low excess air, near stoichiometric fuel/air, or possibly slightly on the rich side.     

A Portable Fiber-Optic Chemical Device for the Quantitative Determination of Carbon Monoxide from Automobile Exhaust Emissions

ABSTRACT

A colorimetxic method for the quantitative determination of CO by diffuse reflectance is described. This method is based on the reduction by CO of Mo (VI) from the indicator reagent molybdosilicic acid (H₈Si[Mo₂O₇]₆). The reduction yielded a change of color from clear yellow to dark green on white disk filter chart paper wetted with reagent indicator solution. The gaseous mixture containing CO was forced to pass through this chart paper, initiating the reaction. The intensity of the color produced, measured by diffuse reflectance, was proportional to the CO concentration present in exhaust gases in the range from 0.02 to 12% volume/volume (v/v). A 650-nm light-emitting diode was used as a light source. A two-fiber-optic system carried the light from the source to the detection system, which was composed of a photodiode, an amplification circuit, and a digital display. The method was applied with success in field measurements for automobiles in the Otto cycle. In a previous paper, this method was used for the quantitative determination of exhaust emissions from diesel-fueled vehicles.¹     

Determination of Nitrogen Oxides in Auto Exhaust

A new procedure for determining nitrogen oxides in automobile exhaust has been developed. The new procedure was included in a Bureau of Mines comparative study that aimed at evaluating various widely used methods for determining NO_x in auto exhaust. The methods included in the evaluation study follow: (1) Static oxidation in tank (ST method). The method involves oxidation of NO in residence with O₂ in a stainless steel tank. (2) Bureau of Mines method (BM method). The method involves application of the ST procedure in exhaust samples from which the hydrocarbons have been removed by combustion over catalyst. (3) Chevron Research method (CR method), as described in the literature. (4) Phenoldisulfonic acid method (PDS method), as described in the literature. The principal objective of this study was to generate experimental evidence which would lead to defining an optimum procedure for converting NO, present in exhaust gas, into NO₂; this conversion is desired so that the total of NO + NO₂ can be determined quantitatively in the form of NO₂. In pursuing this objective, the procedures prescribed by the foregoing methods were comparatively tested. The results indicated that all four methods are subject to error, the extent of which depends on the conditions employed. The BM method was superior from the standpoint of accuracy because it was less affected by interferences due to hydrocarbon-NO₂ reactions.