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PubMed2003

Method for predicting photocatalytic oxidation rates of organic compounds.

In designing a photocatalytic oxidation (PCO) system for a given air pollution source, destruction rates for volatile organic compounds (VOCs) are required. The objective of this research was to develop a systematic method of predicting PCO rate constants by correlating rate constants with physical-chemical characteristics of compounds. Accordingly, reaction rate constants were determined for destruction of volatile organics over a titanium dioxide (TiO2) catalyst in a continuous mixed-batch reactor. It was found that PCO rate constants for alkanes and alkenes vary linearly with gas-phase ionization potential (IP) and with gas-phase hydroxyl radical reaction rate constant. The correlations allow rates of destruction of compounds not tested in this research to be predicted based on physical-chemical characteristics.

Air Pollutants↗
PubMed2002

Organic atmospheric particulate material.

Carbonaceous compounds comprise a substantial fraction of atmospheric particulate matter (PM). Particulate organic material can be emitted directly into the atmosphere or formed in the atmosphere when the oxidation products of certain volatile organic compounds condense. Such products have lower volatilities than their parent molecules as a result of the fact that adding oxygen and/or nitrogen to organic molecules reduces volatility. Formation of secondary organic PM is often described in terms of a fractional mass yield, which relates how much PM is produced when a certain amount of a parent gaseous organic is oxidized. The theory of secondary organic PM formation is outlined, including the role of water, which is ubiquitous in the atmosphere. Available experimental studies on secondary organic PM formation and molecular products are summarized.

Air Pollutants↗
PubMed2003

Flux of organic compounds from grass measured by relaxed eddy accumulation technique.

Fluxes of some Volatile Organic Compounds (VOC) from grass were measured at a golf course in western Sweden, using the Relaxed Eddy Accumulation (REA) technique. The sampling was done by collecting VOC onto adsorbent tubes and the analysis was performed by thermal desorption followed by GC/MS. High emissions were observed after cutting. Transient fluxes of (Z)-3-hexenyl acetate (0.51 microg m(-2) s(-1)), (Z)-3-hexen-1-ol (0.14 microg m(-2) s(-1)) and (Z)-3-hexenal (0.40 microg m(-2) s(-1)) were measured, even at low temperatures. The REA technique requires a relatively large fetch area that is sometimes not available. Therefore, a procedure for correcting measured fluxes from a limited fetch is suggested.

Environmental Monitoring↗
PubMed1990

Determination of volatile organics in drinking water with USEPA method 524.2 and the ion trap detector.

New drinking water regulations require the monitoring of eight volatile organic compounds that have established maximum contaminant levels (MCLs) and 51 other volatile organics for which MCLs are not established. A laboratory analytical method (Method 524.2) for the determination of 58 of these compounds is investigated, and precision and accuracy data are obtained. The method uses a standard inert gas purge extraction, isolation of the volatile organics on a three-stage solid-phase trap, thermal desorption into a gas chromatograph, separation with a fused-silica capillary column, and identification and measurement with a relatively low cost, benchtop ion trap detector that functions as a mass spectrometer. At a concentration of 2 micrograms/L (2 parts per billion), the grand mean measurement accuracy for 54 compounds was 95% of the true value with a mean relative standard deviation (RSD) of 4%. At 0.2 micrograms/L (200 parts per trillion), the grand mean measurement accuracy for 52 compounds was 95% of the true value with a mean RSD of 3%.

Gas Chromatography-Mass Spectrometry↗
PubMed2004

Regulatory off-gas analysis from the evaporation of Hanford simulated waste spiked with organic compounds.

After strontium/transuranics removal by precipitation followed by cesium/technetium removal by ion exchange, the remaining low-activity waste in the Hanford River Protection Project Waste Treatment Plant is to be concentrated by evaporation before being mixed with glass formers and vitrified. To provide a technical basis to permit the waste treatment facility, a relatively organic-rich Hanford Tank 241-AN-107 waste simulant was spiked with 14 target volatile, semi-volatile, and pesticide compounds and evaporated under vacuum in a bench-scale natural circulation evaporator fitted with an industrial stack off-gas sampler at the Savannah River National Laboratory. An evaporator material balance for the target organics was calculated by combining liquid stream mass and analytical data with off-gas emissions estimates obtained using U.S. Environmental Protection Agency (EPA) SW-846 Methods. Volatile and light semi-volatile organic compounds (<220 degrees C BP, >1 mm Hg vapor pressure) in the waste simulant were found to largely exit through the condenser vent, while heavier semi-volatiles and pesticides generally remain in the evaporator concentrate. An OLI Environmental Simulation Program (licensed by OLI Systems, Inc.) evaporator model successfully predicted operating conditions and the experimental distribution of the fed target organics exiting in the concentrate, condensate, and off-gas streams, with the exception of a few semi-volatile and pesticide compounds. Comparison with Henry's Law predictions suggests the OLI Environmental Simulation Program model is constrained by available literature data.

Air Pollutants↗
PubMed2002

Patterns and levels of halogenated volatile compounds in Portuguese surface waters.

The present study focused on monitoring the concentration of 14 halogenated volatile organic compounds in surface waters, including sea, estuarine, river water and industrial effluents in order to determine the most ubiquitous compounds and their concentration levels, which were used to establish their geographical and temporal distribution. EPA Method 502, based on purge and trap techniques, was used. In this method volatile organic pollutants are extracted (purged) from the water sample by bubbling inert gas through the aqueous sample. Purged sample components are trapped in a cartridge containing the polymeric sorbent Tenax and, thereafter, the cartridge is heated and backflushed with helium to desorb the trapped sample components directly into a gas chromatograph with electron capture detector (GC-ECD). The linearity range of the method varied from 0.1 to 4 microg L(-1) with a limit of detection at the low microg L(-1) level. The present study consisted of a monthly monitoring of 46 points throughout Portugal, during 14 months. Chloroform was found in 50% of the samples analyzed, its presence being correlated to both agricultural and industrial activities. Other compounds detected were tetrachloroethylene, trichloroethylene, carbon tetrachloride and 1,2,4 trichlorobenzene, which were present in 10-20% of the samples at concentrations up to 18 microg L(-1). 1,1,2,2-Tetrachloroethane and its degradation product 1,1,2-trichloroethane were found in 5% of the samples, the levels of the latter being higher than those of the parent compound in most samples. Sporadic high concentrations of some volatile halogenated organic compounds were attributed to local uses as solvents.

Agriculture↗
PubMed2004

Design scenario for the radioisotopic estimation of the biogenic component of airborne particles.

An experimental design is described to estimate the fraction of secondary fine particle from the biogenic component of volatile organic compounds (VOCs) in the atmosphere using radiocarbon isotopic abundance ratios. The method distinguishes between "modern" carbon (C), and "old" C of primary and secondary origins based on three components, condensed-phase organic carbon (OC), semi-volatile particulate compounds (SVOCs), and VOCs. The method depends on interpretation of diurnal and seasonal variation in OC, SVOC, and VOC concentrations. Sampling employs a filter-denuder unit, which collects the three C components for isotopic analysis. The samples are collected repetitively for a daily sequence of the same hourly intervals covering diurnal periods with similar meteorological conditions. Collected C is thermally treated to separate OC from black carbon on filters and VOCs or SVOCs from adsorbents, with all four fractions individually oxidized to carbon dioxide to determine the radiocarbon content by accelerator mass spectrometry. Using C isotope abundance, the data are interpreted for fractions of primary modern C and secondary modern C as estimated from averaging diurnal and seasonal variations in the concentration data. As support for interpretation, samples of OC, SVOCs, and VOCs would be analyzed for speciation to identify source indicator species present.

Air Pollutants↗
PubMed2006

Organic compounds in office environments - sensory irritation, odor, measurements and the role of reactive chemistry.

Abstract Sensory irritation and odor effects of organic compounds in indoor environments are reviewed. It is proposed to subdivide volatile organic compounds (VOCs) into four categories: (i) chemically non-reactive, (ii) chemically 'reactive', (iii) biologically reactive (i.e. form chemical bonds to receptor sites in mucous membranes) and (iv) toxic compounds. Chemically non-reactive VOCs are considered non-irritants at typical indoor air levels. However, compounds with low odor thresholds contribute to the overall perception of the indoor air quality. Reported sensory irritation may be the result of odor annoyance. It appears that odor thresholds for many VOCs probably are considerably lower than previously reported. This explains why many building materials persistently are perceived as odorous, although the concentrations of the detected organic compounds are close to or below their reported odor thresholds. Ozone reacts with certain alkenes to form a gas and aerosol phase of oxidation products, some of which are sensory irritants. However, all of the sensory irritating species have not yet been identified and whether the secondary aerosols (ultrafine and fine particles) contribute to sensory irritation requires investigation. Low relative humidity may exacerbate the sensory irritation impact. Practical Implications Certain odors, in addition to odor annoyance, may result in psychological effects and distraction from work. Some building materials continually cause perceivable odors, because the odor thresholds of the emitted compounds are low. Some oxidation products of alkenes (e.g. terpenes) may contribute to eye and airway symptoms under certain conditions and low relative humidity.

Air Pollutants↗
PubMed1998

Selective determination of a group of organic compounds in complex sample matrixes by LC/MIMS with on-line immunoaffinity extraction.

An on-line immunoaffinity extraction with liquid chromatography/membrane introduction mass spectrometry (IAE/LC/MIMS) method for the determination of BTEX compounds in complex sample matrixes is described. This method uses an immunoaffinity column (1 mm i.d. x 20 mm) for on-line sample cleanup and enrichment, a 5-micron C18 trapping column (2 mm i.d. x 20 mm) for analyte focusing, a 3-micron C18 analytical column (3.2 mm i.d. x 100 mm) for separation, and a membrane introduction mass spectrometer for quantitation. The immunoaffinity column was evaluated in terms of binding capacity, recovery, and enrichment factor. The method was optimized for the determination of BTEX compounds in a mixture of 30 volatile organic compounds, which showed no matrix interference and a dramatic improvement of the detection limit over that of the LC/MIMS method (up to 474-fold). This method was also used for the determination of BTEX compounds in several gasoline-contaminated water samples, and the results were compared with the EPA reference methods.

Antibodies↗
PubMed2004

Laser mass spectrometry as on-line sensor for industrial process analysis: process control of coffee roasting.

The objective of the project is to develop on-line, real-time, and noninvasive process control tools of coffee roasting that help deliver a consistent and high-quality coffee aroma. The coffee roasting process was analyzed by direct injection of the roaster gas into a time-of-flight mass spectrometer and ionized either by resonance enhanced multiphoton ionization (REMPI) at 266 and 248 nm or vacuum ultraviolet single-photon ionization (VUV-SPI) at 118 nm. The VUV ionization scheme allows detecting mainly the most volatile and abundant compounds of molecular mass below 100 m/z, while REMPI ionizes mainly aromatic compounds of molecular mass larger than 100 m/z. Combining the compounds ionized by resonant and single-photon ionization, approximately 30 volatile organic compounds are monitored in real time. Time-intensity profiles of 10 important volatile coffee compounds were discussed in connection with their formation chemistry during roasting. Applying multivariate statistics (principle component analysis) on time-intensity traces of nine volatile coffee compounds, the roasting degree could be traced as a consistent path in the score plot of the two most significant principle components (including 68% of the total variance), for a range of roasting temperatures (200-250 degrees C).

Beverages↗
PubMed2004

(Z)-3-Hexenol induces defense genes and downstream metabolites in maize.

In response to insect feeding, corn plants (Zea mays cv. Delprim) release elevated levels of volatile organic compounds (VOCs), including the C(6)-volatile (Z)-3-hexenol. The level of mRNA accumulation for a series of defense genes was monitored in response to application of (Z)-3-hexenol (50 nmol) to undamaged plants. The induction of transcripts for hpl (hydroperoxide lyase), fps (farnesyl pyrophosphate synthase), pal (phenylalanine ammonia-lyase), lox (lipoxygenase), igl (indole-3-glycerol phosphate lyase) and mpi (maize proteinase inhibitor) were compared with metabolites generated from the respective pathways. While headspace VOC analysis showed an increase in (Z)-3-hexenyl acetate and methyl salicylate with lox and pal induction, respectively, MPI accumulation was not observed with an increase in mpi transcripts. Moreover, (Z)-3-hexenol treatment did not elevate sesquiterpene emissions or activate fps transcription. Chemical labeling and bioassay experiments established that exogenous (Z)-3-hexenol can be taken up and converted to a less active acetylated form. These data indicate that (Z)-3-hexenol can serve as a signaling molecule that triggers defense responses in maize and can rapidly be turned over in planta.

Acetates↗
PubMed2006

Electrical discharge machining: occupational hygienic characterization using emission-based monitoring.

Hazardous potential in industrial environments is normally assessed by means of immission-based sampling and analyses. This approach is not adequate, if effects of specific technical adjustments at machine tools or working processes on hygienic parameters should be assessed. This work has focused on the optimization of a manufacturing process (electrical discharge machining, EDM), with regard to risk reduction assessment. It is based on emission analyses rather than immision analyses. Several technical EDM parameters have been examined for their influence on air-based emissions. Worktools and workpieces used have a strong influence on aliphatic compounds and metals but not on volatile organic compounds (benzene, toluene, ethylene-benzene and xylene (BTEX)) and polycyclic aromatic hydrocarbons (PAHs) in air emissions. Increasing the dielectric (mineral oil) level above processing location decreases BTEX, chromium, nickel and PAH emissions. Aliphatic compounds, in contrast, increase in air emissions. EDM current used has a positive relationship with all substances analyzed in air emissions. Indicative immission concentrations, as can be expected under EDM conditions, are estimated in a predictive scenario. The results of this characterization give rise to an important conclusion in that risk assessment so far has been using incorrect parameters: total aliphatic compounds. Maximum level of chromium is reached long before limit values of aliphatic compounds are exceeded. Because of the fact that metals, like chromium, also have a higher hazardous potential, metal analysis should be introduced in future risk assessment. This experimental approach, that captures total emission of the electrical discharge machine, and is not solely based on immission values, has lead to a better understanding of the production process. This information is used to extract recommendations regarding monitoring aspects and protection measures.

Air Pollutants, Occupational↗