Gaseous Organic Compounds Research Articles

Methylated mercury species in municipal waste landfill gas sampled in Florida, USA

Mercury-bearing material has been placed in municipal landfills from a wide array of sources including fluorescent lights, batteries, electrical switches, thermometers, and general waste. Despite its known volatility, persistence, and toxicity in the environment, the fate of mercury in landfills has not been widely studied. The nature of landfills designed to reduce waste through generation of methane by anaerobic bacteria suggests the possibility that these systems might also serve as bioreactors for the production of methylated mercury compounds. The toxicity of such species mandates the need to determine if they are emitted in municipal landfill gas (LFG). In a previous study, we had measured levels of total gaseous mercury (TGM) in LFG in the μg/m 3 range in two Florida landfills, and elevated levels of monomethyl mercury (MMM) were identified in LFG condensate, suggesting the possible existence of gaseous organic Hg compounds in LFG. In the current study, we measured TGM, Hg 0, and methylated mercury compounds directly in LFG from another Florida landfill. Again, TGM was in the μg/m 3 range, MMM was found in condensate, and this time we positively identified dimethyl mercury (DMM) in the LGF in the ng/m 3 range. These results identify landfills as a possible anthropogenic source of DMM emissions to air, and may help explain the reports of MMM in continental rainfall.

Laboratory and field investigation of the adsorption of gaseous organic compounds onto quartz filters

A common method for measuring the mass of organic carbon in airborne particulate matter involves collection on a quartz filter and subsequent thermal analysis. If unaccounted for, the adsorption of organic gases onto quartz filters will lead to the overestimation of aerosol organic carbon concentrations (positive artifact). A recommended method of correction for the positive artifact involves sampling with a backup filter. Placed behind either the primary quartz filter, or behind a Teflon filter and collected in parallel with the primary quartz filter, the carbon content of the quartz backup filter is a measure of the adsorbed organic material on the primary quartz filter. In this paper, we illustrate the application of this technique to samples collected in Berkeley, California. While the tandem quartz filter method can be successfully applied to correct for the positive artifact, we discuss two cases when this method will fail. We have found that the capacity for adsorption of organic gases is not uniform for all filters. Instead, filters manufactured by the same company, but having different lot numbers, exhibit variable adsorption capacity. Thus, a filter pair composed of filters from different lots may lead to significant under- or overestimation of particulate organic carbon concentration. Additionally, we have observed that the tandem filter method under-corrects for the positive artifact if the sampling time is short (few hours). Laboratory experiments with vapors of single organic compounds corroborate results based on ambient samples. The evolution of adsorbed organic gases, particularly polar compounds, during thermal analysis indicates that a single compound may experience two distinct adsorbent–adsorbate binding energies. Adsorbed gases may co-evolve with particles at temperatures in excess of 250°C.

TiO2-coated optical fiber bundles used as a photocatalytic filter for decomposition of gaseous organic compounds

An optical fiber-based, filter-type photocatalytic reactor was designed and the decomposition reaction of gas phase isopropanol was studied using a recirculating reaction system. Compared to the conventional TiO2-coated glass plate or honeycomb monolith, both higher efficiency of light utility and larger processing capacity were obtained. This good combination was achieved by employing both high input light intensities (1.6×1016 to 2.6×1017quantacm−2s−1) and a large number of glass fibers (18000 pieces, 125μm diameter) in the reactor, which makes it possible for the reaction to occur with a high reaction rates while maintaining a high quantum efficiency. These characteristics can be understood by considering a TiO2-coated single fiber as a micro-reactor distributed with low photon flux, and the corresponding fiber bundles being composed of large number of such micro-reactors.

Effects of Mordenite Support on Photodegradation of Gaseous Organic Compounds over TiO2 Photocatalyst

Abstract Effects of mordenite as a support material for TiO2 on photodegradation rates of gaseous propionaldehyde, acetone, and propane were investigated using TiO2 (50 wt%)-loaded mordenite as a photocatalyst in reference to unsupported TiO2. The supported photocatalyst allowed adsorption of all the substrates several times greater than the unsupported photocatalyst, resulting in higher photooxidation rates for them. Detailed analysis suggests that the enhancement of the decomposition rate caused by the use of mordenite support is more remarkable for lower amounts of adsorption of the substrates on the support. The concentration of oxygen was found to have little influence on the photodegradation rates, suggesting that the rate of degradation of the organic substrates was not decided by photogenerated electron transfer processes but by the consumption of photogenerated holes by adsorbed organic substrates.

Volatile organic compound concentration patterns at the New Hendersonville monitoring site in the 1995 Southern Oxidants Study in the Nashville, Tennessee, area

Ambient gaseous organic compounds were monitored on an hourly basis with an automated gas chromatograph from June 15 to 27, 1995, at the New Hendersonville site near Nashville, Tennessee, as part of the Southern Oxidants Study (SOS). These compounds and their estimated average contributions to the total were as follows: isoprene (2.1 ppbC), methyl vinyl ketone (1.1 ppbC), methacrolein (0.6 ppbC), α‐pinene plus β‐pinene (1.3 ppbC), and those nonmethane hydrocarbons, minus isoprene, monitored routinely in the Photochemical Assessment Monitoring Stations (44.6 ppbC). The sum of n‐aldehydes from butanal through nonanal averaged 12.6 ppbC, where a conservative estimate of artifact n‐aldehydes has been subtracted. Strong diurnal variations in the concentrations of n‐aldehydes and the apparent influence of wind shifts on concentration support the existence of n‐aldehydes at significant levels in the ambient air. The empirical fit to data as developed by Jobson et al. [1994] was the upper bound to the loci of maximum isoprene concentrations as a function of temperature and the diurnal variation of the ratio of methyl vinyl ketone to methacrolein was similar to that in studies by Montzka et al. [1993] in the rural southeastern United States. The α‐pinene and β‐pinene concentrations were proportional and α‐pinene concentrations always less than 2 ppbC. In supplemental experiments at a rural site in North Carolina, the α‐pinene concentrations showed a distinctive diurnal pattern with high nighttime values and low midday values. Patterns of concentration for the anthropogenic hydrocarbons benzene, toluene, and o‐xylene versus wind direction showed the impact of a major toluene emitting source as well as the influence of emissions from the direction of Nashville.

Gas-Phase Transport and Sorption of Benzene in Soil

To better understand the transport of gaseous organic compounds through soil near buildings and under high soil gas flow rates in remediation processes, we have studied benzene equilibrium partitio...

Analysis of low-temperature surface discharge plasma products from gaseous organic compounds

Nonequilibrium low-temperature discharge plasma decomposition products of 1000 ppm gaseous organic compounds contaminated in atmospheric pressure air, nitrogen, or oxygen, such as chlorofluorocarbon (CFC-113), organic chloride (trichloroethylene), and carbon tetrachloride, were studied for a better understanding of the decomposition mechanism of the plasma processing. A gas chromatograph-mass spectrometer was used as a main analyzing equipment. When the decomposition rate is not high (20-80%) for CFC-113, many various halogenated carbons or halogenated hydrocarbons are identified as intermediate products by the plasma processing. As the electric discharge power consumption increases, the decomposition rate of CFC-113 increases and intermediate products decrease. At the decomposition rate of more than 90%, some elemental products of hydrochloric acid, carbon dioxide, and nitrogen suboxide are recognized as final products. On the other hand, if the environmental gas is pure nitrogen without any oxygen and water vapor, the decomposition products are still intermediate with sufficient electric discharge power consumption, suggesting the existence of double decomposition mechanisms of nitrogen radicals and oxygen radicals. In the case of trichloroethylene decomposition, harmful intermediate decomposition products were observed when the decomposition rate was 20-90%.

Biological production and consumption of gaseous organic sulphur compounds.

Biological production and consumption of gaseous organic sulphur compounds.

Chemical Emissions in a Thermomechanical Pulp Production Plant

Abstract Following worker reports of irritation, chemical emissions from all production steps in a thermomechanical pulp production plant were studied. Sampling techniques were chosen to allow capture of a wide spectrum of compounds, including gaseous and particulate organic compounds (including terpenes and aldehydes, compounds suspected of causing the reported irritation), total dust, and gases. The only compounds detected in significant concentrations were α- and β-pinene, the primary components of turpentine, a recognized irritant. Carbon monoxide levels reached 15 ppm. The emission sources of these contaminants were random leaks from equipment rather than specific and persistent point sources. A direct-reading photoionizer proved useful in rapidly locating the leaks. The implementation of a program aimed at eliminating and caulking leaks, within the regular maintenance program, would reduce airborne contaminant levels.

Reactions of gaseous organic compounds on silica surface. Spectral studies and synthetic aspects

The results of infrared spectroscopic and mass-spectrometric studies on reactions of vapor phase carboxylic acids, polyazamacrocyclic ligands, pyrimidine bases, acetylacetonates and related compounds with hydroxylic, chlorosilylated, halo- and aminoalkylsilylated silica surfaces are analyzed. Application of various reactions for the gasphase derivatization of silica materials and for the “gassolid-phase” synthesis of 2,5-dioxoperazines is discussed.

Stability of PPB and PPM Organic Cylinder Gases Used for Calibration and Audits

A repository of 39 and 34 gaseous organic compounds in compressed gas cylinders at PPM (5 to 700) and PPB levels (1 to 10,000) respectively has been established by EPA for use in performance audits. In this program, to ensure that the concentration of each gas standard has not changed, each standard is periodically analyzed for stability. The gas mixtures were initially analyzed once or twice by the manufacturer before shipment to Research Triangle Institute (RTI). The gas mixtures were then analyzed at RTI upon receipt from the gas manufacturer and then reanalyzed at 2, 6 and 12 months, and annually thereafter, to determine any change in concentration. An examination of the stability data shows that concentrations for all the organics tested usually varied by less than 10 percent over a period of several years. Ethylene oxide and propylene oxide and trans 1, 4-dichloro-2-butene below the 10 ppb level have been found to be unstable. Six other compounds at the PPM level (aniline, cyclohexanone, p-dichlorobenzene, ethylamine 1, 2-dibromoethylene, and formaldehyde) have been found to be unstable in compressed gas cylinders.

Gas phase retention volume behavior of organic compounds on Carbotrap graphitized carbon

The graphitized carbon material Carbotrap is often used for sampling gaseous organic compounds. Knowledge of the retention volumes of the compounds of interest on Carbotrap is required to design sampling protocols. Published data are examined here to develop correlation equations between retention volume and both vapor pressure and boiling point. The 38 compounds considered included ethane, butane, 1,2-dichloroethane, benzene, trichloroethene, 1,1,2-trichloroethane, phenol, toluene, chlorobenzene, n-butylamine, 4-heptanone, p-dichlorobenzene, decane, n-butylbenzene, biphenyl, n-dodecane, n-tetradecane. The correlation equations are examined in terms of gas—solid adsorption theory. They allow prediction of retention behavior for compounds for which experimental retention data are not yet available.

Summary of POHC Audit Results Using VOST and Bag Methods During RCRA Trial Burns

Audit materials containing Principal Organic Hazardous Constituents (POHCs) have been developed by EPA for use by Federal, State, and Local agencies or their contractors to assess the accuracy of measurement methods used during RCRA trial burn tests. Audit materials are currently available for 27 gaseous organics in five-, six-, seven-, and nine-component mixtures at ppb levels (7 to 10,000 ppb) in compressed gas cylinders in a balance gas of nitrogen. The logic used in selecting 27 gaseous organic compounds as audit materials and how these audit materials are successfully used in performance audits is described. Stability studies indicate that all of the organics tested (with the exception of ethylene oxide and propylene oxide below 10 ppb levels) are stable enough to be used as reliable audit materials. As of January 1990, 215 performance audits have been conducted to assess the accuracy of Volatile Organic Sampling Train (VOST) and bag measurement methods during or prior to RCRA trial burn tests. A sum...

Seasonal surface ozone and filterable bromine relationship in the high Arctic

Ozone and filterable bromine measurements in the high Arctic during the spring return of solar radiation suggest a rapid concurrent destruction of O 3 and conversion of gaseous to particulate Br. Multiyear observations show that this pattern is an annual feature of O 3 measured near the surface at Barrow, Alaska, and other Arctic locations. Aircraft measurements show low O 3 amounts and high filterable Br concentrations beneath the surface temperature inversion over ice throughout the Arctic in the spring. A wintertime build-up of the gaseous organic compound bromoform and a rapid depletion of bromoform in the spring may be a link between the episodic O 3 depletion events and the accompanying rise in filterable Br.

Performance audit results for volatile POHC measurements during RCRA trial burn tests.

Audit materials containing principal organic hazardous constituents (POHCs) have been developed by EPA for use by federal, state, and local agencies or their contractors to assess the accuracy of measurement methods used during RCRA trial burn tests. Audit materials are currently available for 27gaseous organics in five, six, seven, and nine-component mixtures at parts-per-billion levels (7 to 10,000 ppb) in compressed gas cylinders in a balance gas of nitrogen. The criteria used for the selection of 27 gaseous organic compounds is described. Stability studies indicate that all of the organics tested (with the exception of ethylene oxide and propylene oxide below 10 ppb levels) are stable enough to be used as reliable audit materials. Subsequent to completion of the stability studies, 89 performance audits have been conducted with the audit materials to assess the accuracy of the Volatile Organic Sampling Train (VOST) and bag measurement methods during or prior to RCRA trial burn tests. A summary of the a...

Evaluation of Parts-per-billion Organic Cylinder Gases for Use as Audits During Hazardous Waste Trial Burn Tests

A repository of 14 gaseous organic compounds at parts-per-billion levels (7-430 ppb) in compressed gas cylinders has been established by the Environmental Protection Agency. This repository was established to provide audit materials for use in conducting performance audits to assess the accuracy and precision of principal organic hazardous constituent (POHC) measurements, especially those performed during hazardous waste trial burn tests. Five- and nine-component mixtures In a balance gas of nitrogen were prepared in aluminum cylinders for use in the performance audit program. The five-component mixtures contain carbon tetrachloride, chloroform, perchloroethylene, vinyl chloride, and benzene. The ninecomponent mixtures contain trichloroethylene, 1,2-dichloroethane, 1,2-dibromoethane, acetonitrile, trichlorofjuoromethane, dichlorodifluoromethane, bromomethane, methyl ethyl ketone and 1,1,1-trichloroethane. Studies of all 14 gaseous organic compounds were performed to determine the stability of the compound...

Quality Assurance for Principal Organic Hazardous Constituents (POHC) Measurements during Hazardous Waste Trial Burn Tests

A repository of 14 gaseous organic compounds at ppb levels in compressed gas cylinders has been established by the Environmental Protection Agency. This repository was established to provide audit materials for use in performance audits to assess and document the accuracy and precision of POHC measurements during hazardous waste trial burn tests. From this repository, gas cylinders containing five organic compounds in a balance gas of nitrogen were used to conduct performance audits during this study. The five compounds were: carbon tetrachloride, chloroform, perchloroethylene, vinyl chloride, and benzene. Stability studies of the five compounds were performed. Results indicate that all five are adequately stable for use as reliable audit materials. Subsequent to completion of the stability studies, performance audits were conducted to assess the accuracy and precision of the Volatile Organic Sampling Train (VOST) and bag measurement methods. The audit results indicate that laboratories can use these methods to analyze POHC with accuracy to within the ±50% limits stated in the VOST protocol.

The use of principal components analysis for the investigation of an organic air pollutants data set

Principal components analysis (PCA) was used for the investigation of an air pollutants data base. The data set consists of nearly 400 measurements of 26 gaseous organic compounds and meteorological data. The measurements were carried out at four different places in The Netherlands. PCA is a simple way to display visually most of the total variation in a few dimensions. It is helpful in the identification of outliers, the recognition of sources and the investigation of meteorological effects.

Evaluation of Selected Gaseous Halocarbons for Use in source Test Performance Audits

A repository of 38 gaseous organic compounds in compressed gas cylinders has been established by EPA. This repository was established to provide standards for source test performance audits, that is, quantitative quality assurance tests. Among these compounds are ten halogenated organic species, which are the focus of this paper. Stability studies of all ten compounds have been performed to determine the feasibility of using them as performance audit standards. Results indicate that all of the halocarbons tested are adequately stable to be used as reliable audit standards. Subsequent to completion of stability studies, four of the ten halocarbons were used in source test performance audits. Results are available at this time for two of the four compounds; the results show agreement within 10% of the concentrations previously established by Research Triangle Institute.

Activities of various sulfide catalysts in the hydrogenation and hydrolysis of carbon disulfide to hydrogen sulfide

Catalysts for the conversion of gaseous organic sulfur compounds were prepared by impregnating the surface of activated aluminum hydroxide catalyst (AS-64) with various metallic sulfides. It was found that a molybdenum sulfide surface possessed the maximum activity of all the metal systems tested, and that it was far superior to untreated AS-64.