Search results for "Volatile"
showing 10 items of 606 documents
The Amazonian boundary layer and mesoscale circulations
2009
Numerous biogenic volatile organic compounds (VOC) species are released into the atmosphere from tropical forests. Measuring all those which are relevant for atmospheric chemistry or for the carbon budget is challenging. Large-Scale Biosphere-Atmosphere (LBA) Experiment field campaigns substantially increased the number of field studies of isoprene and monoterpene emissions, as well as of the exchange of several other VOC species. This chapter reports about the progress made within LBA from primary emission measurements at the plant species level up to discussions of the oxidative capacity of the atmosphere and formation of secondary organic aerosol particles and cloud condensation nuclei f…
Adsorption of chlorinated volatile organic compounds on hydrophobic faujasite: correlation between the thermodynamic and kinetic properties and the p…
1998
This work deals with a thermodynamic and kinetic study of the adsorption of single volatile organic compounds (VOCs) (dichloromethane (DCM), 1,2-dichloroethane (DCA), trichloroethene (TCE) and tetrachloroethene (PCE)) on a dealuminated faujasite Y by simultaneous measurements of the adsorbed amounts, adsorption heats and diffusivities. The type V isotherms and the weak values of derivative enthalpies allowed us to predict that the competitive adsorption of their mixture would be similar to a distillation. This prediction was verified experimentally: the breakthrough curves of VOC mixtures showed that the adsorbate with the higher boiling point displaced the adsorbate with the lower boiling …
Effects of solvent-free microwave extraction on the chemical composition of essential oil of Calamintha nepeta (L.) Savi compared with the convention…
2008
The essential oil of Calamintha nepeta has been obtained by solvent-free microwave extraction (SFME) and by classical hydrodistillation (HD). A comparative qualitative-quantitative study on the composition of the oils was carried out. A total of 38 compounds, constituting 97.6% of the oil, were identified in the oil obtained by SFME, whereas 46 compounds, representing 95.4% of the oil, were characterized in the HD oil. SFME-distilled oil is richer in lightly oxygenated monoterpenes (LOM) than HD oil. It also has a higher amount of sesquiterpenes and a lower quantity of hydrocarbon monoterpenes. HD oil seems to be affected by chemical changes more than SFME oil.
Biological effects of short-chain fatty acids in nonruminant mammals.
1993
propionate, volatile fatty acids (VFAs), cholesterol, cell prolifera tion, human gastric lipase
Oxygen-containing polycyclic aromatic hydrocarbons (OPAHs) in urban soils of Bratislava, Slovakia: patterns, relation to PAHs and vertical distributi…
2011
Abstract We determined concentrations, sources, and vertical distribution of OPAHs and PAHs in soils of Bratislava. The ∑14 OPAHs concentrations in surface soil horizons ranged 88–2692 ng g−1 and those of ∑34 PAHs 842–244,870 ng g−1. The concentrations of the ∑9 carbonyl-OPAHs (r = 0.92, p = 0.0001) and the ∑5 hydroxyl-OPAHs (r = 0.73, p = 0.01) correlated significantly with ∑34 PAHs concentrations indicating the close association of OPAHs with parent-PAHs. OPAHs were quantitatively dominated by 9-fluorenone, 9,10-anthraquinone, 1-indanone and benzo[a]anthracene-7,12-dione. At several sites, individual carbonyl-OPAHs had higher concentrations than parent PAHs. The concentration ratios of se…
Removal of TEX vapours from air in a peat biofilter: influence of inlet concentration and inlet load
2006
This paper presents the results of the study of the removal of toluene, ethylbenzene, and o-xylene (TEX) by biofiltration using a commercial peat as filter-bed material. Runs with a single organic compound in air, and with the mixture of TEX in air, were carried out for at least 55 days in laboratory-scale reactors inoculated with a conditioned culture. The influence of organic compound inlet load and of gas flow rate on the biofilter's performance was studied, including relatively high values of pollutant inlet concentration (up to 4.3 gC m−3 for ethylbenzene, 3.2 gC m−3 for toluene, and 2.7 gC m−3 for o-xylene). Results obtained show maximum elimination capacities of 65 gC m−3 h−1 for o-x…
Benzene, toluene, ethyl benzene and xylenes in ambient air and Pinus sylvestris L. needles: a comparative study between Belgium, Hungary and Latvia
2001
Abstract Concentrations of benzene, toluene, ethyl benzene and xylenes (BTEX) in ambient air and in 1 yr old Pinus sylvestris pine needles were monitored along a busy road, petrol station and rural area of Belgium, Hungary and Latvia in a 1 yr period. To test P. sylvestris as a possible biomonitor for the BTEX concentrations, samples were taken in the four seasons. As the distribution of data was not normal, the level of pollution on different sites and seasons was compared and evaluated by non-parametric tests. The measured air concentrations did not differ significantly from one season to another throughout the year. There were, however, differences between sampling places. The C2-alkylbe…
Analysis of odour and taste problems in high-density polyethene
1998
Abstract The compounds that cause off-flavours in plastics, have been recognized mainly as carbonyl compounds (aldehydes, ketones and esters). They occur in low concentrations, and due to their low-threshold odour concentrations, their typical odours were identified. Most of these off-flavour compounds are volatile. Chemical analysis of smelling compounds requires a very sensitive method with a high-resolution capability. The analysis of volatile organic compounds (VOCs) in high density polyethene (HD-PE) granules and waters in which the granules have been shaken for 4 h, were carried out by gas chromatography–mass spectrometry–sniffing system (GC–MS–SNIFF) and by gas chromatography–fourier…
Quantitative Comparison of Free and Bound Volatiles of Two Commercial Tomato Cultivars (Solanum lycopersicumL.) during Ripening
2009
The changes in the profile of both free and glycosidically bound volatiles were studied in Moneymaker and Raf tomato cultivars during fruit ripening. The concentrations of 20 of 24 and of 27 of 30 compounds detected in the free volatile fraction (FVF) and glycosidically bound fraction (GBF), respectively, differed significantly between cultivars during ripening. Most free and bound volatiles increased during ripening in both cultivars. The contribution of each free volatile compound to the overall aroma was estimated by calculating its log U value, which indicated that only 11 compounds seem to exert a strong influence. Nine volatiles were detected exclusively in the GBF, among them geranio…
UV photocatalytic oxidation of paint solvent compounds in air using an annular TiO2-supported reactor
2010
BACKGROUND: One of the most important industrial sources of volatile organic compounds (VOCs) is related to coating and painting applications. In this sense, photocatalytic oxidation can become an innovative and promising alternative for the remediation of air polluted by VOCs. In this study the UV photodegradation of m-xylene, toluene and n-butyl acetate, as representative compounds of paint solvents, was carried out in an annular reactor using a TiO2–glass wool supported catalyst. RESULTS The removal of each component and their mixture, simulating an industrial emission, was evaluated under different operational conditions. A maximum elimination capacity of 12, 18 and 80 mg C m−3 s−1 was …