Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 3.496
Filtrar
1.
J Environ Manage ; 271: 110997, 2020 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-32778285

RESUMO

Gas ebullition in sediment results from biogenic gas production by mixtures of bacteria and archaea. It often occurs in organic-rich sediments that have been impacted by petroleum hydrocarbon (PHC) and other anthropogenic pollution. Ebullition occurs under a relatively narrow set of biological, chemical, and sediment geomechanical conditions. This process occurs in three phases: I) biogenic production of primarily methane and dissolved phase transport of the gases in the pore water to a bubble nucleation site, II) bubble growth and sediment fracture, and III) bubble rise to the surface. The rate of biogenic gas production in phase I and the resistance of the sediment to gas fracture in phase II play the most significant roles in ebullition kinetics. What is less understood is the role that substrate structure plays in the rate of methanogenesis that drives gas ebullition. It is well established that methanogens have a very restricted set of compounds that can serve as substrates, so any complex organic molecule must first be broken down to fermentable compounds. Given that most ebullition-active sediments are completely anaerobic, the well-known difficulty in degrading PHCs under anaerobic conditions suggests potential limitations on PHC-derived gas ebullition. To date, there are no studies that conclusively demonstrate that weathered PHCs can alone drive gas ebullition. This review consists of an overview of the factors affecting gas ebullition and the biochemistry of anaerobic PHC biodegradation and methanogenesis in sediment systems. We next compile results from the scholarly literature on PHCs serving as a source of methanogenesis. We combine these results to assess the potential for PHC-driven gas ebullition using energetics, kinetics, and sediment geomechanics analyses. The results suggest that short chain 

Assuntos
Petróleo , Gases/análise , Sedimentos Geológicos , Hidrocarbonetos , Metano
2.
Ecotoxicol Environ Saf ; 202: 110920, 2020 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-32800255

RESUMO

Advanced glycation end products (AGE) and the receptor for AGE (RAGE) have been found to be pivotal biomarkers to predict the risk of inflammation and oxidative stress. Limited evidence focuses on the influence of occupational exposure to polycyclic aromatic hydrocarbon (PAH) and metal fumes on AGE and RAGE in shipyard welders. Our aim was to determine the relationships among PAH, metal exposure, and inflammatory biomarkers. From September 1 to December 31, 2017, 53 welding workers (exposed group) and 29 office workers (control group) were enrolled in the study. Comprehensive workups included demographic characteristics, laboratory data, AGE, RAGE, Interleukin-6 (IL-6), tumor necrosis factor-α, PAH, and urinary metal concentrations. RAGE levels were measured by flow cytometric analysis. Urinary 1-hydroxypyrene (1-OHP) was used as a biomarker of exposure to PAH. Several metals were elevated in the personal fine particulate matter (PM2.5) samples, including Mn, Fe, V, Co, Zn, and Cu. The exposed group had significantly higher exposure to PM2.5 (p = 0.015), RAGE (p = 0.020), IL-6 (p = 0.008) than the control group. After adjusting for pertinent variables, there was still a significant and positive association between Ni level and AGE (ß = 0.101; 95% CI, 0.031-0.172). Significant relationship between Cr and Cd levels and RAGE was observed (ß = 0.173; 95% CI, 0.017-0.329; ß = 0.084; 95% CI, 0.011-0.157, respectively). Participants with elevated 1-OHP level had higher odds of high RAGE level in the model 1 (OR = 3.466, 95% CI, 1.053-11.412) and model 2 (OR = 3.454, 95% CI, 1.034-11.536). The RAGE expression of participants was significantly associated with IL-6 levels in the fully adjusted model (ß = 0.294; 95% CI, 0.083-0.732). Our findings highlighted that urinary metal levels and PAH were associated with increased AGE and RAGE formation in shipyard workers. Elevated serum RAGE might induce the production of proinflammatory cytokines and trigger ensuing inflammatory cascades.


Assuntos
Poluentes Ocupacionais do Ar/análise , Metais/análise , Exposição Ocupacional/análise , Hidrocarbonetos Policíclicos Aromáticos/análise , Receptor para Produtos Finais de Glicação Avançada/metabolismo , Poluentes Ocupacionais do Ar/toxicidade , Biomarcadores/urina , Gases/análise , Produtos Finais de Glicação Avançada/sangue , Humanos , Inflamação , Masculino , Metais/toxicidade , Estresse Oxidativo , Material Particulado/análise , Hidrocarbonetos Policíclicos Aromáticos/toxicidade , Fator de Necrose Tumoral alfa , Soldagem
3.
J Chromatogr A ; 1626: 461355, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797835

RESUMO

Quantification of the gas streams from chemical systems such as catalytic reactors are routinely performed by on-line gas chromatography. Gas chromatographs used for this purpose are typically provided with a combination of thermal conductivity (TCD) and flame ionization (FID) detectors to be able to detect and quantify both permanent gases; COx, N2, H2, etc., and hydrocarbons. However, the accuracy of the quantification is hindered by the intrinsic limitations of each type of detector. Namely, TCD has low sensitivity and FID does not detect permanent gases. Therefore, modern gas chromatographs include methanizer units to partially overcome this shortcoming by converting COx to methane. However, as far as these authors know, the literature has not presented an analytical method to characterize gas streams with high accuracy by the simultaneous use of a combination of a TCD-FID detection system provided with a methanizer. This work is an attempt to solve this problematic; it consists of the formulation of a mathematical model for the well-known external and internal standard quantification methods in gas chromatography. The analysis of the gas stream from a catalytic reactor performing the combustion of methane was used to validate the developed method. The concentration ranges of the analysed gases were: 0.8-7.7 vol% of CH4, CO2, and CO, 7.7-38.5 vol.% of O2, and 46.2-90.8 vol.% of N2 at a total flow of 130 mL min-1. It was found that the commonly applied external standard method leads not only to inaccurate quantification but also to physically meaningless carbon balances and conclusions on the behaviour of the selected model system. In contrast, the internal standard method led to a highly accurate quantification with a physically meaningful carbon balance. Considering these findings, this contribution also draws attention to the need for a thoughtful application of chromatographic methods when studying the reactivity of gas systems.


Assuntos
Cromatografia Gasosa/métodos , Gases/análise , Sistemas On-Line , Carbono/análise , Catálise , Ionização de Chama , Metano/análise , Oxigênio/análise , Padrões de Referência , Reprodutibilidade dos Testes , Condutividade Térmica
4.
PLoS One ; 15(8): e0237836, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32841245

RESUMO

Lake Kivu, East Africa, is well known for its huge reservoir of dissolved methane (CH4) and carbon dioxide (CO2) in the stratified deep waters (below 250 m). The methane concentrations of up to ~ 20 mmol/l are sufficiently high for commercial gas extraction and power production. In view of the projected extraction capacity of up to several hundred MW in the next decades, reliable and accurate gas measurement techniques are required to closely monitor the evolution of gas concentrations. For this purpose, an intercomparison campaign for dissolved gas measurements was planned and conducted in March 2018. The applied measurement techniques included on-site mass spectrometry of continuously pumped sample water, gas chromatography of in-situ filled gas bags, an in-situ membrane inlet laser spectrometer sensor and a prototype sensor for total dissolved gas pressure (TDGP). We present the results of three datasets for CH4, two for CO2 and one for TDGP. The resulting methane profiles show a good agreement within a range of around 5-10% in the deep water. We also observe that TDGP measurements in the deep waters are systematically around 5 to 10% lower than TDGP computed from gas concentrations. Part of this difference may be attributed to the non-trivial conversion of concentration to partial pressure in gas-rich Lake Kivu. When comparing our data to past measurements, we cannot verify the previously suggested increase in methane concentrations since 1974. We therefore conclude that the methane and carbon dioxide concentrations in Lake Kivu are currently close to a steady state.


Assuntos
Gases/análise , Lagos/química , África Oriental , Dióxido de Carbono/análise , Metano/análise , Pressão , Risco
5.
J Chromatogr A ; 1625: 461267, 2020 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-32709320

RESUMO

We describe the design and performance evaluation of a portable gas chromatograph suitable for the analysis of volatile organic and odorous compounds at trace levels. The system comprises a carbon nanotube sponge preconcentrator, an electronic pressure control (EPC) unit, a temperature-programmable column module, and a fast-response photoionization detector. A built-in tablet computer controls instrumental parameters and chromatogram display functions. The compact GC with dimensions of 35 cm (l) × 26 cm (w) × 15 cm (h) is self-contained, weighing less than 5 kg without a battery pack, and uses no auxiliary compressed gases. Our design has three main advantages over conventional portable GCs: recharging configuration of ambient air as the carrier gas using a miniature diaphragm pump, precise control of column flow by the built-in canister and EPC system, and rapid thermal desorption of the preconcentrator facilitated by intrinsic resistivity of the carbon nanotube sponge. A 30 m, 0.28 mm I.D. capillary column operated at a head pressure of 14 psi provided a peak capacity of 55 for a 10 min isothermal analysis. The temperature-programmability feature could decrease the analysis time of less than 5 min for vapor mixture of benzene, toluene, ethylbenzene, and o-xylene. More than a 100-fold increase in sensitivity by preconcentrating a sample adsorption volume of 90 mL resulted in improved detection limits of 0.13 (benzene), 0.20 (toluene), 0.23 (ethylbenzene), and 0.28 (o-xylene) ppb (v/v). Our instrument displayed good stability and reproducibility of retention times (< 0.14% RSD) and intensities (< 4.5% RSD) for continuous measurements using the preconcentrator over 10 h. Thus, continuous and on-site determinations of trace volatile organic compounds in air samples with this instrument appear feasible.


Assuntos
Poluentes Atmosféricos/análise , Cromatografia Gasosa/métodos , Sistemas Computacionais , Hidrocarbonetos Aromáticos/análise , Compostos Orgânicos Voláteis/análise , Calibragem , Gases/análise , Limite de Detecção , Nanotubos de Carbono/química , Odorantes/análise , Pressão , Reprodutibilidade dos Testes , Temperatura , Fatores de Tempo
6.
Ecotoxicol Environ Saf ; 201: 110855, 2020 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-32540620

RESUMO

Total dissolved gas (TDG) supersaturation generated by discharged flood water may cause the death of fish downstream of dams and severely threaten their survival during the flood season. No study has performed to investigate the effects of TDG on fish dwelling in shallows in China. Furthermore, varied TDG levels are caused by the varied flow of flood water during the spill season. Fish may alternatingly experience intermittent TDG exposure from equilibrated water and TDG-supersaturated water. However, little research on the effects of intermittent TDG exposure on fish has been conducted. To evaluate the tolerance of fish to continuous acute TDG exposure, juvenile yellow catfish living in the shallows were exposed to TDG-supersaturated water at 125%, 130%, 135% and 140% TDG for 96 h. The results showed that the juvenile yellow catfish exhibited obvious gas bubble disease (GBD) and abnormal behaviours (e.g., exophthalmos and bubbles on fins). The survival probability declined with the arising TDG levels. The median survival time (ST50) of yellow catfish was 8.57, 18.1, 33.86 and 58.84 h at above TDG levels, respectively. To further investigate the effects of intermittent TDG exposure on juvenile yellow catfish, the fish were subjected to varied TDG levels (125%, 130%, 135% and 140%) for a specific duration (3 h and 6 h) and then underwent a period of recovery (3, 6 and 9 h) in equilibrated water. The results showed that an increase in recovery time (or decreasing exposure time) can prolong the survival time of yellow catfish and improve their survival probability at the same exposure time (or same recovery time). Compared with that under continuous acute exposure, the ST50 of juvenile yellow catfish increased significantly with intermittent exposure. Intermittent exposure can enhance the tolerance of juvenile yellow catfish to TDG. The application of the results may contribute to the protection of aquatic organisms and the formulation of the scheme of reservoir operation in the Yangtze River.


Assuntos
Adaptação Fisiológica/efeitos dos fármacos , Peixes-Gato/fisiologia , Gases/toxicidade , Rios/química , Poluentes da Água/toxicidade , Animais , Comportamento Animal/efeitos dos fármacos , China , Gases/análise , Probabilidade , Análise de Sobrevida , Movimentos da Água , Poluentes da Água/análise , Qualidade da Água
7.
Waste Manag ; 113: 186-196, 2020 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-32535371

RESUMO

An 8 ton/day solid refuse fuel gasification process with air oxidant was operated under various conditions to generate electricity. Solid refuse fuels with fluff type feedstock were fabricated from municipal solid wastes. The tested experimental conditions included feedstock charging rate into the gasifier, equivalence ratio, and oxygen enrichment; varying these conditions resulted in different gasification characteristics, such as cold gas efficiency and carbon conversion ratio. Optimum conditions were a charging rate of 50 to 60% by volume (504.71 to 605.65 kg/Sm2) of feedstock in the gasifier, equivalence ratio of 0.21 to 0.33, and no oxygen enrichment. Average cold gas efficiency and carbon conversion ratio were 71.30% and 72.07%, respectively, at optimum conditions. Pollutants such as dust, tar, and gases, were analyzed at the outlet of the cleaning facility and gasifier, and their low concentrations in the producer gas were sufficient to allow for operation of the gas engine. The gasification process exhibited stable operation over 288 h, which included the facility check period. The average gasifier temperature was 825 °C, 17.14% by volume of producer gas was syngas, and gas engine power generation was 235 kWh during this period; power consumption of the entire system was 68 kWh. These results demonstrate that the gasification process for converting solid waste to energy can be operated at a commercial scale.


Assuntos
Resíduos de Alimentos , Eliminação de Resíduos , Eletricidade , Gases/análise , Resíduos Sólidos/análise
8.
Chemosphere ; 257: 127168, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32480089

RESUMO

Waste incineration is a preferred method in China to dispose the municipal solid waste, but controlling the production of highly toxic polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans effectively during incineration is both challenging and imperative. In this study, the suppression of PCDD/Fs by various phosphorus-containing compounds was explored, and the mechanisms responsible for the inhibition were studied in detail. The experiments took place in a lab-scale vertical tubular reactor at 350 °C under a simulated flue gas (12 vol% O2 in N2 flow), and both the off-gases and residues were collected for PCDD/Fs analysis. The scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to characterize the reaction residues. The experimental results revealed that NH4H2PO4 and (NH4)2·HPO4 showed the highest inhibitory effect (57.2% and 57.3%, respectively) on the PCDD/Fs formation, followed by CaHPO4 with inhibition efficiency of 39.1%. In contrast, KH2PO4 and K2HPO4 barely inhibited the generation of the PCDD/Fs. The inhibitory effect of NH4H2PO4 and (NH4)2·HPO4 was similar to that of nitrogen-based inhibitors. At the same time, it was proven that the inhibitory activity of CaHPO4 might be due to the reaction of it with Cu2+ forming stable compounds.


Assuntos
Dibenzofuranos Policlorados/toxicidade , Dibenzofuranos/toxicidade , Dibenzodioxinas Policloradas/toxicidade , China , Cinza de Carvão/química , Dibenzofuranos Policlorados/química , Gases/análise , Incineração/métodos , Fósforo , Compostos de Fósforo , Dibenzodioxinas Policloradas/análise , Resíduos Sólidos
9.
Environ Sci Pollut Res Int ; 27(28): 35416-35427, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32594447

RESUMO

Vapor intrusion (VI) risk assessments determine the cleanup level of groundwater in the absence of ingestion. In recent VI investigations, the building pressure cycling (BPC) method has been applied to help minimize ambiguity caused by temporal variability of indoor air samples that are important to risk assessments, and, consequently, determine groundwater cleanup level accurately. In this study, we use a three-dimensional numerical model to examine the dynamic migration of VOCs from groundwater after the application of BPC. First, we validated the numerical model with field measurements. Then, the verified model is used to investigate the effects of site-specific features in determining the performance of BPC operation. At last, we summarize past field applications of BPC to examine the simulated results. Our study indicates that the BPC-induced indoor depressurization can increase the building loading rate in the first 2-3 h, which would then drop to 2-3 times of that with natural conditions in most cases of groundwater contamination. In some cases involving a strong source, e.g., a vapor source above the capillary fringe or a groundwater source with sandy soil above the groundwater level, the normalized building loading rates can be maintained as high as 4-9 without decrease after the first 2-3 h. Significantly higher increase in building loading rate may indicate a potential presence of a preferential pathway between the groundwater contamination and concerned building.


Assuntos
Água Subterrânea , Poluentes do Solo , Gases/análise , Medição de Risco , Solo
10.
Waste Manag Res ; 38(10): 1110-1118, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32564700

RESUMO

Sustainable solid waste management can provide pathways for renewable energy generation. The Kingdom of Bahrain has witnessed burgeoning municipal solid waste (MSW) generation rate due to socio-economic development. The authorities of this Small Island Developing State, which is located in arid environment, plan to produce 5% of the total electricity demand from renewable energy sources by 2025 and then double it to 10% by 2035. The US Environmental Protection Agency's Landfill Gas Emission Model software was used to estimate the generation of biogas from MSW at the Askar Landfill site. Results envisaged that maximum landfill gas (LFG) emission rates will be in 2020 following landfill closure by the end of 2019, as an intentional scenario, with a maximum electricity generation potential of 57.4 GWh that could provide power to 488 households. Revenues from carbon credits and electricity sales were US$97.8 million and US$64.8 million, respectively, for the period 2020-2035. The internal combustion engine exhibited the most viable option based on economic analysis of the cost of alternative LFG energy recovery technologies. Our work highlights the potential to use LFG-to-energy technologies to reduce the carbon footprint in arid climates for developing countries with substantial electricity subsidization.


Assuntos
Eliminação de Resíduos , Gerenciamento de Resíduos , Barein , Gases/análise , Metano/análise , Resíduos Sólidos/análise , Instalações de Eliminação de Resíduos
11.
J Chromatogr A ; 1622: 461096, 2020 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-32359779

RESUMO

The main focus of the present research was the on-line coupling of two separation techniques, namely liquid chromatography (LC) and gas chromatography (GC). For such an analytical combination, a dedicated interface is required to remove solvent from the sample, leaving the latter in a sharp band at the head of the GC column. Considering such an objective, a lab-developed LC-GC interface is herein presented, based on the use of a six-port two-position valve and a programmed-temperature-vaporizing (PTV) injector. The PTV injector was derived from a commercial split/splitless injector body, heated using a resistance heating wire, and enabled a satisfactory recovery of low boiling compounds (≤ C13), working in the normal-phase mode. The lab-developed PTV injector allowed the use of a larger-volume liner (compared to the commercial one initially used), it being characterized by dimensions 95 mm length × 5.0 mm O.D. × 3.4 mm I.D. and a volume of 862 µL, thus facilitating the transfer of larger LC fractions. The developed system is fully automatized and controlled without the use of additional software. The interface was evaluated and used for the analysis of mineral oil saturated hydrocarbons in vegetable oils. Detection was carried out by using a flame ionization detector (FID), with quantification performed through external calibration, across the 5-1000 mg kg-1 range. The LC-GC-FID method linearity, limits of detection and quantification, accuracy and precision were measured. The resulting limits of detection and quantification values were 0.4 and 1.3 mg kg-1, respectively. The average accuracy at the 100 mg kg-1 level was 95.5% (ranging between 93.3 and 99.7%). Intra-day repeatability at levels of 5 and 100 mg kg-1 were 2.4% and 3.5%, respectively.


Assuntos
Técnicas de Química Analítica , Cromatografia Gasosa , Técnicas de Química Analítica/instrumentação , Técnicas de Química Analítica/métodos , Ionização de Chama , Gases/análise , Hidrocarbonetos/análise , Limite de Detecção , Óleo Mineral/análise , Óleos Vegetais/química , Reprodutibilidade dos Testes , Solventes/análise , Temperatura
13.
J Chromatogr A ; 1622: 461122, 2020 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-32376021

RESUMO

To understand the overall processes behind the decomposition of state-of-the-art organic liquid electrolytes in lithium ion batteries (LIBs), it is necessary to investigate and quantify the permanent gases and light hydrocarbons evolving during electrolyte decomposition. In this work a convenient way of sampling gas from pouch cells without any previous preparation of the cell as well as a comprehensive gas chromatographic (GC) investigation of the gas phase is shown. A barrier discharge ionization detector (BID) was utilized for gas quantification and a multi component gas standard in combination with a gas mixing device was implemented to prepare calibration standards for validation. Therefore, sensitivity, linearity and reproducibility as well as the limits of detection (LOD) and limits of quantification (LOQ) were determined. Gas samples from pouch cells using LiNi0.6Mn0.2Co0.2O2 as cathode material and natural graphite (NMC622 ∣∣ NG) as anode material were analysed after formation. Gas volume and gas composition are key factors for a sufficient formation of LIBs and of interest for research with respect to the development of new materials and additives.


Assuntos
Cromatografia Gasosa/métodos , Fontes de Energia Elétrica , Gases/análise , Lítio , Cobalto , Eletrodos , Eletrólitos/química , Grafite , Íons , Limite de Detecção , Lítio/química , Manganês , Níquel , Reprodutibilidade dos Testes
14.
Chemosphere ; 255: 126958, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32388262

RESUMO

Secondary nonferrous metal smelters are important sources of unintentionally produced persistent organic pollutants (UPOPs) including polychlorinated biphenyls (PCBs), polychlorinated naphthalenes, pentachlorobenzene, and hexachlorobenzene. Quantifying UPOP emissions by the main sources is an important step when evaluating UPOP emissions and establishing an inventory. In this study, field investigations were performed to allow UPOP emissions and distributions in stack gases emitted by secondary nonferrous metal smelters to be compared. A total of 25 stack gas samples were collected from secondary copper smelters (SCus), secondary zinc smelters, and secondary lead smelters in China. The mean toxic equivalent concentrations (TEQs) and mass concentrations of most of the UPOPs were highest in the secondary zinc smelter stack gas samples, next highest in the SCu stack gas samples, and lowest in the secondary lead smelter stack gas samples. The mean dioxin-like PCB and polychlorinated naphthalene TEQs were ∼8.9 and ∼6.6 times higher in stack gases from a SCu equipped with an oxygen-enriched smelting furnace than in stack gases from a SCu with a converter furnace. The mean PCB-118 to PCB-123 ratios and CN-10 to CN-35 ratios varied strongly and could be used as diagnostic ratios for apportioning the sources of UPOPs in the environment. Emission factors for dioxin-like PCBs, polychlorinated naphthalenes, pentachlorobenzene, and hexachlorobenzene in stack gases from secondary nonferrous metal smelters were derived and updated. The results improve our understanding of UPOP emission and provide data for establishing UPOP emission inventories for secondary nonferrous metal smelters.


Assuntos
Poluentes Atmosféricos/análise , Monitoramento Ambiental , Metalurgia , Clorobenzenos , Cobre , Dioxinas/análise , Gases/análise , Hexaclorobenzeno , Naftalenos , Bifenilos Policlorados , Dibenzodioxinas Policloradas/análise
15.
Environ Sci Technol ; 54(12): 7117-7125, 2020 06 16.
Artigo em Inglês | MEDLINE | ID: mdl-32408743

RESUMO

Controlled pressure method (CPM) testing is a building-specific diagnostic tool for vapor intrusion (VI) pathway assessment which offers advantages over traditional pathway assessment approaches. By manipulating the building pressure conditions, the CPM creates the worst-case VI impact and provides rapid insight into the type of vapor source(s). The primary barrier to general acceptance and use of this tool is the need for definitive guidance on test design parameters, such as the indoor-outdoor pressure difference (or exhaust fan flow rate), CPM test duration, exhaust fan location, and air sampling location(s) and conditions. This study focused on a systematic evaluation of each of these factors, which then led to the formulation of proposed CPM testing guidelines. The results suggest that CPM tests should be conducted with both negative and positive pressure indoor-outdoor differentials of about 10-15 Pa, and the tests should last for at least nine indoor air exchanges for negative pressure difference testing and four indoor air exchanges for positive pressure difference testing. Although exhaust fan intake sampling is sufficient to provide critical information to assess impacts during negative pressure testing, adding room-specific indoor air sampling to both negative and positive pressure difference testing can provide insight into vapor entry locations and indoor source contributions.


Assuntos
Poluentes Atmosféricos , Poluição do Ar em Ambientes Fechados , Poluentes Atmosféricos/análise , Poluição do Ar em Ambientes Fechados/análise , Gases/análise , Emissões de Veículos
16.
Chemosphere ; 253: 126651, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32283424

RESUMO

This study investigated the characteristics of dl-PCNs, PCDD/Fs and dl-PCBs emitted from two typical secondary copper metallurgical plants processing copper sludge equipped with different sets of air pollution control devices (APCDs). Results indicated that the emission factors of dl-PCNs and PCDD/Fs of plant A are 0.00775 and 1.09 µg TEQ/ton, respectively, which are remarkably lower than those of plant B (3.12, 181 and 25.5 µg TEQ/ton for dl-PCNs, PCDD/Fs and dl-PCBs, respectively). Dl-PCNs contributed 0.7-2.7% of total TEQ for flue gases and up to 2.6% of TEQ for ash samples. The TEQ concentration of dl-PCNs in fly ash individually exceeds the regulated level of 1 ng TEQ/g regulated by Taiwan EPA, indicating that emission and discharge of dl-PCNs should be regulated. The combination of semidry scrubber and activated carbon injection (ACI) + baghouse (BH) is effective for simultaneous removals of dl-PCNs and PCDD/Fs in plant A; while the combination of cyclone, secondary combustion chamber, ACI + BH and wet scrubber (WS) is not optimal for removing dl-PCNs, PCDD/Fs and dl-PCBs. Memory effect occurring within BH and WS is responsible for low removal efficiencies of these POPs in plant B. This study suggests appropriate APCDs for simultaneous removal of three POP groups and recommends the inclusion of dl-PCNs in emission standard.


Assuntos
Poluentes Atmosféricos/análise , Monitoramento Ambiental , Metalurgia , Cinza de Carvão/análise , Cobre/química , Dibenzofuranos/química , Dibenzofuranos Policlorados/análise , Gases/análise , Bifenilos Policlorados/análise , Dibenzodioxinas Policloradas/análise , Esgotos , Taiwan
17.
Food Chem ; 324: 126893, 2020 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-32344336

RESUMO

An Au patch electrode Ag-SnO2/SiO2/Si MIS capacitive sensor equipped with a microcontroller was designed and developed to sense low concentration (ppb to ppm regime) of volatiles (NH3, TMA, ethanol, and H2S) generated from chicken meat spoilage at room temperature. The quality threshold or the acceptance limit for consumption of chicken meat samples stored at 4 °C, 15 °C and 25 °C using our proposed technique was found to be 105 h, 48 h, and 17 h respectively, highly correlated with TVB-N, TVC, pH and sensory evaluation analysis. When these well established standard methods (TVB-N, TVC and pH analysis) take many hours to complete the analysis involving many complicated steps, our fabricated sensor takes 55 sec to deliver sensing response reflecting the meat spoilage status. The sensor calibrated with our compact technique promises portable and inexpensive onsite rapid and accurate quality assessment of meat spoilage at room temperature.


Assuntos
Gases/análise , Ouro/química , Carne/análise , Semicondutores , Amônia/análise , Animais , Galinhas , Eletrodos , Qualidade dos Alimentos , Sulfeto de Hidrogênio/análise , Concentração de Íons de Hidrogênio , Silício/química , Dióxido de Silício/química , Prata/química , Temperatura , Compostos de Estanho/química
18.
Chemosphere ; 251: 126345, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32169696

RESUMO

This study aimed at investigating whether stable isotopes can be used to monitor the progress of volatile organic compounds (VOCs) volatilization from contaminated sediment during venting. Batches of a dry aquifer sediment were packed into stainless steel HPLC columns, humidified with distilled water and later contaminated by either liquid toluene or propan-2-ol. The VOCs were then volatilized by a stream of gas at room temperature, and the concentrations and stable isotope ratios of gaseous VOCs were recorded by isotope-ratio mass spectrometry. During early stages of volatilization of toluene, the isotope ratios Δδ13C shifted to more negative values by about -3 to -5‰ and the Δδ2H by more than -40‰, while the concentration remained at or near initial saturated vapor concentration. Depletion of the isotope ratios in the gas was explained by the vapor-liquid fractionation process, which is amplified by successive self-partitioning steps of gaseous VOC into remaining liquid VOC. For propan-2-ol the carbon isotope shift was negative like for toluene, whereas the H shift was positive. Hydrogen bonding in the liquid propan-2-ol phase causes a normal vapor-liquid H isotope effect which was described already in classical literature. The isotope shifts in the present experiments are larger than previously reported shifts due to phase-change processes and reach the magnitude of shifts usually observed in kinetic isotope fractionation.


Assuntos
2-Propanol/química , Água Subterrânea/química , Tolueno/química , Carbono , Isótopos de Carbono/análise , Fracionamento Químico/métodos , Gases/análise , Hidrogênio/análise , Ligação de Hidrogênio , Areia , Tolueno/análise , Compostos Orgânicos Voláteis/análise , Volatilização
19.
J Breath Res ; 14(4): 046006, 2020 07 21.
Artigo em Inglês | MEDLINE | ID: mdl-32153262

RESUMO

Offline breath analysis by thermal desorption gas chromatography mass spectrometry (TD-GC-MS) requires the use of sorbent traps to concentrate and store volatile compounds. The selection of which sorbent to use and best practices for managing high relative humidity are important considerations to allow for reproducible, untargeted, biomarker discovery in water saturated breath samples. This work aims to assess three commonly used sorbent materials for their use in breath volatile sampling and determine how the high relative humidity inherent in such samples effects the capture of volatile compounds of interest. TenaxGR, TenaxTA/Carbograph1TD and TenaxTA/Carbograph5TD tubes were selected as they are the most commonly used sorbents in the breath sampling literature. The recovery of 29 compounds in a standard mix loaded using high humidity gas was tested for each sorbent and compared to loading in dry gas. Water retention and dry purge rates were determined for each sorbent for 500 ml and 1000 ml breath collections. Finally, breath samples were collected simultaneously on to each sorbent type using the ReCIVA and analysed by TD-GC-MS. All three sorbents exhibited acceptable reproducibility when loaded with the standard mix in dry gas (RSD < 10%). Loading the standard mix in humid gas led to reduced recovery of compounds based on their chemical properties. Dry purging performance for each sorbent material was assessed and was shown to be 1.14, 1.13 and 0.89 mg H2O min-1 for TenaxGR, TenaxTA/Carbograph1TD and TenaxTA/Carbograph5TD respectively when flushed with 50 ml min-1 of N2. A comparison of breath profiles on different sorbents showed differences in background artefacts (sulfur dioxide, cyclopenten-1-one and 3-nonene) and endogenous breath compounds (2-methyl-furan and furfural). This work demonstrates that high relative humidity during sampling reduces the ability of sorbent tubes to capture volatile compounds and could impact method detection limits during breath sampling. Sufficient water to impair accurate analysis was retained on all tubes. Minimal differences were observed between sorbent materials when used to sample breath, however, suggestions are provided for sorbent selection for future studies.


Assuntos
Testes Respiratórios/instrumentação , Testes Respiratórios/métodos , Umidade , Compostos Orgânicos Voláteis/análise , Adsorção , Análise Discriminante , Gases/análise , Interações Hidrofóbicas e Hidrofílicas , Análise de Componente Principal , Reprodutibilidade dos Testes , Água
20.
J Vis Exp ; (156)2020 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-32065156

RESUMO

In situ infrared spectroscopy is an inexpensive, highly sensitive, and selective valuable tool to investigate the interaction of polycrystalline solids with adsorbates. Vibrational spectra provide information on the chemical nature of adsorbed species and their structure. Thus, they are very useful for obtaining molecular level understanding of surface species. The IR spectrum of the sample itself gives some direct information about the material. General conclusions can be drawn concerning hydroxyl groups, some stable surface species and impurities. However, the spectrum of the sample is "blind" with respect to the presence of coordinatively unsaturated ions and gives rather poor information about the acidity of surface hydroxyls, species decisive for the adsorption and catalytic properties of the materials. Furthermore, no discrimination between bulk and surface species can be made. These problems are solved by the use of probe molecules, substances that interact specifically with the surface; the alteration of some spectral features of these molecules as a result of adsorption provides valuable information about the nature, properties, location, concentration, etc., of the surface sites. The experimental protocol for in-situ IR studies of gas/sample interaction includes preparation of a sample pellet, activation of the material, initial spectral characterization through the analysis of the background spectra, characterization by probe molecules, and study of the interaction with a particular set of gas mixtures. In this paper we investigate a zirconium terephthalate metal organic framework, Zr6O4(OH)4(BDC)6 (BDC = benzene-1,4-dicarboxylate), namely UiO-66 (UiO refers to University of Oslo). The acid sites of the UiO-66 sample are determined by using CO and CD3CN as molecular probes. Furthermore, we have demonstrated that CO2 is adsorbed on basic sites exposed on dehydroxylated UiO-66. Introduction of water to the system produces hydroxyl groups acting as additional CO2 adsorption sites. As a result, CO2 adsorption capacity of the sample is strongly enhanced.


Assuntos
Dióxido de Carbono/análise , Gases/análise , Estruturas Metalorgânicas/química , Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Poluentes Químicos da Água/análise , Água/química , Zircônio/química , Adsorção , Dióxido de Carbono/química , Dióxido de Carbono/metabolismo , Estruturas Metalorgânicas/metabolismo , Espectrofotometria Infravermelho
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA