Evaluation of Probes Used for Source Sampling of Hydrogen Fluoride

The body of information presented in this paper is directed to those individuals concerned with methods for the sampling and measurement of fluorides contained in stack gases produced during the manufacture of phosphate fertilizer or aluminum. An air stream containing gaseous hydrogen fluoride (HF), at concentrations of from 87 to 1700 µg F m^-3, was generated and passed through 193 to 198 cm lengths of Pyrex glass, type 316 stainless steel, TFE Teflon, and methyl methacrylate-coated aluminum probes at flow rates of 28 I min^-1. HF passing through the probes was collected in deionized water contained in a Greenburg-Smith impinger. The Teflon probe exhibited no loss of HF and no trend toward increased passage of HF with time. Significant amounts of fluoride were lost in 18 out of 20 tests with the methacrylate probe and in 4 out of 20 tests with the Pyrex and stainless steel probes. Trends toward increased passage of HF with time occurred with the latter three probe materials. The selective ion electrode and semiautomated methods gave equivalent results when samples were made alkaline to avoid sorption of fluoride by Tygon tubing used in the semiautomated method. These results demonstrated that a Teflon probe gave the most representative sample of gaseous HF. However, additional tests are needed before a final recommendation is made for a probe to sample fluorides in stack gases.     

Correction for water vapor in the measurement of atmospheric trace gases

The presence of water vapor in a sample of air reduces the concentration of a trace gas measured from the sample. We present a methodology to correct for this effect for those cases when the concentration of the trace gas has already been measured from a wet sample. The conversion or correction factor that takes the wet mole fraction to a dry mole fraction is determined by the mixing ratio of water vapor inside the sampling canister. For those samples where the water vapor is saturated inside the canister, the water vapor mixing ratio is largely determined by laboratory conditions; for the unsaturated samples, the mixing ratio is determined by station conditions. If the meteorology at the sampling station is known, the equations presented here can be used directly to calculate the appropriate correction factor. For convenience, we use climatological data to derive average monthly correction factors for seven common global sampling sites: Barrow, AK, US (71 degrees N, 157degrees W); Cape Meares, OR, US (45 degrees N, 124 degrees W); Mauna Loa, HI, US (19 degrees N, 155 degrees W); Ragged Point, Barbados (13 degrees N, 59 degrees W); American Samoa (14 degrees S, 171 degrees W); Cape Grim, Tasmania, Australia (41 degrees S, 145 degrees E); South Pole (90 degrees S). These factors adjust wet mole fractions upwards within a range of 0.002% for the South Pole to over 0.8% for saturated sites. We apply the correction factors to wet nitrous oxide (N2O) mole fractions. The corrected data are more consistent with our understanding of N2O sources.     

Variation of the Relative Humidity of Air Released from Canisters after Ambient Sampling

ABSTRACT

Dalton's law of partial pressures and the hypothesis that water vapor equilibrium in a canister is identical to that established above liquid water are used to predict the variation of the percent relative humidity (%RH) of air released from canisters used in ambient air sampling, typically 6-L canisters pressurized with 18 L of air. When (and if) the water vapor partial pressure in a canister exceeds its saturation vapor pressure, water vapor condensation begins and the condensation rate equals the sampling rate of water vapor into the canister. Under constant temperature conditions, the air subsequently released from the canister is less humid than the original sample, following the relationship %RH = 100% (6 L/V_s) for V_s> V_r, where V_s is the residual air volume (referenced to atmospheric pressure), and V_r is shown to depend on the %RH of the ambient air sample. V_r is the residual air volume at which water is completely removed (except for adsorbed water vapor) from the canister wall. For V_s < V_r, the predicted %RH is constant and equal to its value at V_r. Experimental values agree reasonably well with predictions at both high (90%) and low (34%) RH. However, experimental values are often slightly displaced (usually towards lower values of %RH) for mid-range %RH (61%) and variations in %RH near V_r change from canister to canister.     

Vapor-Phase and Fine Particulate Matter Concentrations of Polycyclic Aromatic Hydrocarbons Measured during the Winter Months in a Northern Rocky Mountain Urban Airshed

Abstract

A fine particulate matter (PM_2.5) sampling program was conducted in Missoula, MT, to investigate both the particle and vapor phases of PM_2.5-associated polycyclic aromatic hydrocarbons (PAHs) found in a northern Rocky Mountain urban airshed. Twenty-four-hour samples were collected during the cold winter months of January through April 2002, when many of the more volatile organic components of PM_2.5 were expected to be found in the condensed particle form. To meet analytical detection limits, each of the 12 individual sample days were aggregated into four total filter and polyurethane foam (PUF) samples, respectively, with each aggregate containing 3 sample days. Quartz filter (particle-phase PAHs) and PUF (vapor-phase PAHs) aggregates were analyzed separately for 18 individual PAHs and phenolics by gas chromatography/mass spectrometry. Results showed that 87% of the PM_2.5-associated phenolics and PAHs measured in this study were found in the vapor phase. PM_2.5-associated gas/particle partition coefficients (K_p,2.5) ranged from 0 for the lighter phenolics and PAHs to ~0.1 for some of the heavier PAHs, such as fluoranthene and pyrene. Calculating K_p,2.5 for the heaviest measured PAHs was not feasible because of low or undetectable concentrations in the vapor phases of these compounds. Phenolics and two-ringed and three-ringed PAHs were found almost exclusively in the vapor phase. Four-ringed PAHs were distributed between the particle and vapor phases, with more mass measured in the vapor phase. Very little five-ringed and higher PAHs were measured from either the filter or PUF sampling medium. These results provide information on both the concentrations and different phases of PM_2.5-associated PAHs measured during the winter months in a northern Rocky Mountain urban airshed, when concentrations of PM_2.5 are generally at their highest compared with the rest of the year.     

Issues Related to Solution Chemistry in Mercury Sampling Impingers

ABSTRACT

Analysis of Hg speciation in combustion flue gases is often accomplished in standardized sampling trains in which the sample is passed sequentially through a series of aqueous solutions to capture and separate oxidized Hg (Hg²⁺) and elemental Hg (Hg⁰). Such methods include the Ontario Hydro (OH) and the Alkaline Mercury Speciation (AMS) methods, which were investigated in the laboratory to determine whether the presence of Cl₂ and other common flue gas species can bias the partitioning of Hg⁰ to front impingers intended to isolate Hg²⁺ species. Using only a single impinger to represent the front three impingers for each method, it was found that as little as 1-ppm Cl₂ in a simulated flue gas mixture led to a bias of approximately 10-20% of Hg⁰ misreported as Hg²+ for both the OH and the AMS methods. Experiments using 100-ppm Cl₂ led to a similar bias in the OH method, but to a 30-60% bias in the AMS method. These false readings are shown to be due to liquid-phase chemistry in the impinger solutions, and not necessarily to the gas-phase reactions between Cl₂ and Hg as previously proposed. The pertinent solution chemistry causing the interference     

强化水旋澄清池技术处理黄河高浊度水的试验研究

由于兰州段夏季黄河水的浊度较高,直接影响了自来水厂的正常运行,而目前水厂所用工艺无法满足高浊度水的处理要求,因此,采用自主研究开发的具有特殊结构的水旋澄清池对黄河高浊度水进行了强化处理的试验研究.研究结果表明:在多点投药混合方式下,强化水旋澄清池可提高浊度的处理效果;若在投加无机絮凝剂PAC后,再投加有机絮凝剂PAM进行复配作用,不仅可降低无机絮凝剂的用量,节约制水成本,而且提高了自来水厂的出水水质;结果也表明该水旋澄清池技术能够推广应用于黄河高浊度水的强化处理工艺中.     

Effects of soil moisture and physical-chemical properties of organic pollutants on vapor-phase transport in the vadose zone

Vapor-phase transport of organic pollutants is one of the important pathways in the distribution and attenuation of volatile organic compounds in the vadose zone. In this study, the impact of vapor-phase partitioning and of the physical-chemical properties of organic pollutants on vapor-phase transport was assessed. An experimentally derived relationship to predict vapor sorption for a variety of soil types under varying soil moisture conditions was incorporated into the two-dimensional finite-element model, Vocwaste. The revised model was then used to simulate the transport of volatile organics. Vapor-phase partitioning in the model accounted for vapor uptake by sorption onto moist mineral surfaces as well as sorption at the liquid-solid interface and dissolution into soil water. Under dry conditions, vapor-phase sorption of volatile organic pollutants was shown to have a retarding effect on transport of organic vapors. However, for shallow, contaminated soils, volatilization was controlled by vapor diffusion, even under dry conditions where vapor-phase sorption was high. The influence of Henry's law constant and of the aqueous-phase (solid-liquid) partition coefficient for volatile organic pollutants was considered in the simulations. Volatilization of organic vapors was shown to be favored for contaminants with high Henry's law constants and low aqueous-phase partitioning coefficients. Because of the interdependence of these two physical-chemical properties, individual properties of the contaminant should not be considered in isolation in the evaluation of vapor transport.     

诱导结晶法去除地下水中氟离子简

针对现行高氟地下水处理工艺中存在的工艺复杂、运行管理困难等问题,提出采用诱导结晶法除氟。其技术核心是在高氟水中投加氟磷灰石作为晶种,并投加磷酸盐和钙盐使水中氟离子在晶种表面生成氟磷酸钙（Ca₁₀（PO₄） ₆F₂）结晶。通过单因素实验得出最佳工艺条件：投加8g/L氟磷灰石,并投加NaH₂PO₄和CaCl₂,使钙离子、磷酸根离子和氟离子的摩尔比为10：5：1,搅拌速度为100 r/min,反应时间1 h。反应中磷酸根离子和钙离子的利用率分别达到98%和25%以上。电子扫描显微镜（SEM）表征晶种在参与反应后,表面有结晶生成。研究表明,采用诱导结晶法可将水中氟离子浓度从5~10 mg/L降至1 mg/L以下,达到饮用水水质标准。     

The Effects of Liquid Water Addition In Gas Turbine Combustors

The addition of liquid water, in quantities equivalent to the mass of fuel consumed, exerts thermal and chemical effects upon the combustion process in a gas turbine engine. The thermal influence is produced by the vaporizalion and heating of the water and its vapor. The final temperature is reduced and the concentrations of NO _x , O, OH, CO are lower than standard combustion concentrations. Chemically, the additional H₂O participates in reactions producing the aforementioned species. However, the lower temperature overrides this influence. These effects have been assessed for different fuel states, i.e., for pre-mixed combustion and for liquid fuel undergoing vaporization and mixing.     

Estimating Overall Sample Train Efficiency

A common part of many gas analyses using bubblers is to combine the contents of the first n-1 impingers and analyze them separate from the nth. The nth impinger, yielding as it should a nil result, confirms that all of the sample entering the train was caught and that the concentration calculated therefrom represents the “true” value.

Many a hapless analyst has found himself stuck with nonzero nth impingers on occasion. Bemgloath tb reject the whole test, the analyst will often report the concentration based on the total catch (with appropriate qualifiers, of course). Another common practice is to calculate the percentage of the total catch in the first n-1 impingers. Sometimes this is reported, erroneously, as the sampler efficiency. The true sampler efficiency cannot be known (if it is less than 100%) because the presence of sample in the last impinger indicates that some unknown amount has passed through the train entirely.     

Particle-Molecule Collection by Sonic Flow Impingers

The information presented in this paper is directed to those industrialists and researchers interested in molecule and near micron and submicron particle sampling by a convenient, inexpensive, and sufficiently accurate method. The use of two sonic flow impingers in series is predicted to collect 98-99% of a phosphoric acid aerosol having a mass median diameter of 0.7 p. The first impinger of a new design is shown, in field sampling, to collect simultaneously 90-98% of the aerosol and 95% of molecular fluoride compounds. On the same aerosol, the standard Greenburg-Smith impinger shows a low collection performance, less than 50% at 1 cfm and 65% at sonic velocity. The use of a first impinger at sonic flow greatly simplifies sampling procedures by eliminating the need for a test meter and associated pressure and temperature measurements. Also, for small particle sizes isokinetic sampling is not necessary and sampling line losses by deposition are shown to be less than 1%. The low initial cost of the sampling units and the low manpower requirements for setting up and supervising sampling make possible the taking of a number of samples sufficient to establish emissions over extended intervals of time. The equipment is especially suited to locations having multiple emission sources, or for locations requiring simultaneous sampling of many points.     

The Microdetermination of Fluoride in Vegetation

This paper describes a micro method for the determination of the fluoride content of plant materials, particularly the leaves. The samples are dried and ground to a fine powder. Fifty milligram samples are burned in oxygen in 250-ml separatory funnels or in 300-ml Erienmeyer flasks. The gaseous products of the combustion are absorbed in 0.1 N NaOH in the closed funnel or flask and transferred to a small covered plastic dish in which the fluoride is diffused to tiny droplets of 3N sodium hydroxide solution distributed over the lower side of a tight fitting cover. The diffused fluoride is dissolved in water and determined colori-metrically by the SPADNS reagent.     

Kinetics of Catalytic Oxidation of Benzene,n-Hexane,and Emission Gas from a Refinery Oil/Water Separator over a Chromium Oxide Catalyst

ABSTRACT

With the advances made in the past decade, catalytic incineration of volatile organic compounds (VOCs) has become the technology of choice in a wide range of pollution abatement strategies. In this study, a test was undertaken for the catalytic incineration, over a chromium oxide (Cr₂O₃) catalyst, of n-hexane, benzene, and an emission air/vapor mixture collected from an oil/water separator of a refinery. Reactions were carried out by controlling the feed stream to constant VOC concentrations and temperatures, in the ranges of 1300–14,700 mg/m³ and 240–400 ° C, respectively. The destruction efficiency for each of the three VOCs as a function of influent gas temperature and empty bed gas residence time was obtained.

Results indicate that n-hexane and the oil vapor with a composition of straight- and branch-chain aliphatic hydrocarbons exhibited similar catalytic incineration effects, while benzene required a higher incineration temperature or longer gas retention time to achieve comparable results.

In the range of the VOC concentrations studied, at a given gas residence time, increasing the operating temperature of the catalyst bed increased the destruction efficiency. However, the much higher temperatures required for a destruction efficiency of over 99% may be not cost-effective and are not suggested. A first-order kinetics with respect to VOC concentration and an Arrhenius temperature dependence of the kinetic constant appeared to be an adequate representation for the catalytic oxidation of these volatile organics. Activation energy and kinetic constants were estimated for each of the VOCs. Low-temperature destruction of the target volatile organics could be achieved by using the Cr₂O₃ catalyst.     

Analysis of VOCs in Ambient Air Using Multisorbent Packings for VOC Accumulation and Sample Drying

Abstract

Solid multisorbent packings have been characterized for trapping and release efficiency of trace (10-20 ppbv in humidified zero air) volatile organic compounds (VOCs). The use of a two-stage trapping system reduces sample water content typically by more than 95.5% while maintaining a trapping and release efficiency of 100% for 49 VOCs, including eight water-soluble VOCs. Three combinations of primary tube and focusing tube are examined in detail by using an atomic emission detector to monitor hydrogen as an indication of residual water vapor, and to monitor either chlorine, bromine, or carbon for target VOCs. Linearity of response to individual VOCs, the presence of artifacts, and a laboratory monitoring application are also discussed.     

Pathways for the oxidation of sarin in urban atmospheres

The nerve agent sarin has recently been deployed by terrorists in a major city. The molecule is volatile and made its way to many victims by passing as vapor through a highly reactive medium. Here we estimate rates and pathways for the removal of gas phase sarin from a generalized urban atmosphere. Only information from the open scientific literature is used. By structure reactivity comparisons with the organophosphorus pesticides, hydroxyl radical hydrogen abstraction may occur in as little as one hour. Decomposition of side chains after hydroxyl attack leads to organic oxygenates which preserve the phosphonofluoridate and so toxicity. The aqueous aerosol surface is contacted in minutes and offers access to a range of dissolved nucleophiles. Substitution displaces the fluoride leaving group, giving safe phosphoric acid analogs. Because of uncertainties in the electron distribution and in aqueous decay mechanisms, the time constants must be viewed as lower limits.     

Recommendations on a Preferred Procedure for the Determination of Particulate in Gaseous Emissions

Studies were made over a 3 year period to evaluate the EPA Method 5 manual particulate sampling procedure in the forest products industry through laboratory and field studies. Results of the study showed that several modifications could be made to improve the performance and suitability of the method for routine source particulate measurements. Physical system changes included the use of a Teflon-lined umbilical cord to the collection system. Procedure changes included changing the isokinetic sampling rate variations to ±20% for emission sources where the particles were smaller than three micrometers in aerodynamic diameter, purging the impinger solutions with an inert gas immediately following collection, and separate evaporation of impinger organics and inorganics at 25 °C and 105°C, respectively. Calculation changes included inclusion of impinger-caught particulate and separate consideration of inorganic and organic particulates.     

The Effect of Water Vapor on Ozone Synthesis in the Photo-oxidation of Alpha-pinene

A study of the effect of water vapor on the photochemical system NO₂ + alphapinene + hv was conducted. A Hotpack Environmental Room was used as a constant temperature chamber, a bank of ultraviolet and fluorescent lamps as a source of simulated solar radiation, and a 150-liter FEP Teflon bag as a reaction vessel. Representative concentrations of 10 pphm NO₂ and 50 pphm alphapinene were used in a 3 × 2 × 2 factorial design where absolute humidities of 0.0000, 0.0090, 0.01 80 g H₂O/g dry air were varied.

Matheson zero air was passed through a clean air train and used as the diluent. Nitrogen dioxide was added to the reaction mixture by a permeation tube, and water and alpha-pinene by evaporation techniques.

Variables measured as a function of time over a 2-hour irradiation period were total oxidants (Mast Ozone Meter), condensation nuclei (General Electric Small Particle Detector), ozone (Regener Chemiluminescent Ozone Meter), nitrogen dioxide and nitric oxide (Technicon Autoanalyzer), and alpha-pinene (Perkin- Elmer Model 800 gas chromatograph).

Upon irradiation, systems containing nitrogen dioxide and alpha-pinene formed oxidants, ozone, condensation nuclei, and nitric oxide. Based on the differences between simultaneous oxidant and ozone measurements, the formation of peroxide- like compounds may be inferred. During the course of the irradiation, nitrogen dioxide and alpha-pinene were consumed. The concentration-time profiles of all variables were characteristic of those exhibited by typical photochemical smog systems.

An effect of water vapor on the systems studied was demonstrated. Increasing humidity decreased net mean/time oxidant and ozone production and net maximum condensation nuclei production. These effects were significant at a 0.05 confidence level. Effects of water on average mean/time NO₂, NO, and alphapinene concentrations were insignificant at this level. The oxidant to ozone ratio was found to decrease with increasing humidity.

The significant decreases in net oxidant and ozone production and NO₂ consumption with increasing water vapor concentration in systems of nitrogen dioxide alone, suggests that water manifests an effect on pertinent inorganic reactions, and the data also suggest additional water participation in the organic reactions.     

Cincinnati’s Radioactive Fallout Monitoring Program

A fluoride analyzer originally designed by Wiggins, St. John, Thomas arid associates at Stanford Research Institute, has been modified to improve its operational capabilities and reliability so as to operate for periods in excess of six months with virtually no maintenance. It measures hydrogen fluoride in the atmosphere in the sub-parts per billion range. The need for the instrument, method of measuring fluoride and the modifications made to improve the SRI instrument are presented. The instrument has been operated in the field for two years beside impingers which obtain daily integrated samples. The impingers samples are subsequently titrated. Satisfactory correlation has been found between the average daily values by the automatic analyzer and the impinger.     

Non-aqueous phase liquid spreading during soil vapor extraction

Many non-aqueous phase liquids (NAPLs) are expected to spread at the air-water interface, particularly under non-equilibrium conditions. In the vadose zone, this spreading should increase the surface area for mass transfer and the efficiency of volatile NAPL recovery by soil vapor extraction (SVE). Observations of spreading on water wet surfaces led to a conceptual model of oil spreading vertically above a NAPL pool in the vadose zone. Analysis of this model predicts that spreading can enhance the SVE contaminant recovery compared to conditions where the liquid does not spread. Experiments were conducted with spreading volatile oils hexane and heptane in wet porous media and capillary tubes, where spreading was observed at the scale of centimeters. Within porous medium columns up to a meter in height containing stagnant gas, spreading was less than ten centimeters and did not contribute significantly to hexane volatilization. Water film thinning and oil film pinning may have prevented significant oil film spreading, and thus did not enhance SVE at the scale of a meter. The experiments performed indicate that volatile oil spreading at the field scale is unlikely to contribute significantly to the efficiency of SVE.     

Investigation of the positive artifact formation during sampling semi-volatile aerosol using wet denuders

Wet denuders are used in several steam-based semi-continuous aerosol monitors to avoid gaseous absorption artifacts and pre-humidify the air stream, while simultaneously allowing measurements of water-soluble gaseous species. Unlike dry denuders, wet denuders saturate the sample air stream with water vapor, which can lead to re-partitioning of water-soluble volatile species to the aerosol phase, thereby causing a positive artifact in aerosol measurements. This paper investigates the magnitude of the positive artifact formation occurring in wet denuders using modeling techniques. Gaseous nitric acid was used as an example of volatile water-soluble gas in both flat and annular wet denuders. We have also verified the occurrence of the positive artifact in a flat wet denuder through a laboratory experiment. The model results indicate that the magnitude of the artifact is rather limited under typical conditions being less than 2.5% of ambient nitric acid concentration for the flat denuder and less than 0.6% for the annular denuder. The magnitude of the artifact increases with condensational sink of the aerosol (i.e. with the mean aerosol size and number concentration) and aerosol water solubility. While the artifact is relatively small in the absolute sense, it could be substantial for aerosol nitrate measurements, especially in ammonia limited conditions, when the concentration of the nitric acid is high and the concentration of nitrate is low. Therefore, we recommend that the artifact is assessed regularly by replacing the wet denuder with a dry denuder.