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31.
Development of an adaptable headspace sampling method for metabolic profiling of the fungal volatome
Stephen J Fowler, Nicholas D Read, Royston Goodacre, Michael J Bromley, Tamara M Nijsen, Oluwasola Lawal, Iain R White, Pavlos Geranios, Waqar M Ahmed, 2018, izvirni znanstveni članek

Opis: Pulmonary aspergillosis can cause serious complications in people with a suppressed immune system. Volatile metabolites emitted by Aspergillus spp. have shown promise for early detection of pathogenicity. However, volatile profiles require further research, as effective headspace analysis methods are required for extended chemical coverage of the volatome; in terms of both very volatile and semi-volatile compounds. In this study, we describe a novel adaptable sampling method in which fungal headspace samples can be sampled continuously throughout a defined time period using both active (pumped) and passive (diffusive) methods, with the capability for samples to be stored for later off-line analysis. For this method we utilise thermal desorption-gas chromatography-mass spectrometry to generate volatile metabolic profiles using Aspergillus fumigatus as the model organism. Several known fungal-specific volatiles associated with secondary metabolite biosynthesis (including α-pinene, camphene, limonene, and several sesquiterpenes) were identified. A comparison between the wild-type A. fumigatus with a phosphopantetheinyl transferase null mutant strain (ΔpptA) that is compromised in secondary metabolite synthesis, revealed reduced production of sesquiterpenes. We also showed the lack of terpene compounds production during the early growth phase, whilst pyrazines were identified in both early and late growth phases. We have demonstrated that the fungal volatome is dynamic and it is therefore critically necessary to sample the headspace across several time periods using a combination of active and passive sampling techniques to analyse and understand this dynamism.
Ključne besede: Volatile Organic Compounds, Fungi, Mycelial growth
Objavljeno: 18.07.2019; Ogledov: 54; Prenosov: 0
.pdf Polno besedilo (712,24 KB)

32.
TD/GC–MS analysis of volatile markers emitted from mono- and co-cultures of Enterobacter cloacae and Pseudomonas aeruginosa in artificial sputum
Craig Portsmouth, Pedro Povoa, Jan H Leopold, Pouline M P van Oort, Emili Diaz, Gemma Goma, Timothy Felton, Paul Dark, Alan Davie, Luis Coelho, Lieuwe D Bos, Marta Camprubi, Antonio Artigas, Jonathan Barnard-Smith, Waqar M Ahmed, Stephen J Fowler, Tamara M E Nijsen, Royston Goodacre, Weda Hans, Hugo knobel, Oluwasola Lawal, Iain R White, 2018, izvirni znanstveni članek

Opis: Introduction: Infections such as ventilator-associated pneumonia (VAP) can be caused by one or more pathogens. Current methods for identifying these pathogenic microbes often require invasive sampling, and can be time consuming, due to the requirement for prolonged cultural enrichment along with selective and differential plating steps. This results in delays in diagnosis which in such critically ill patients can have potentially life-threatening consequences. Therefore, a non-invasive and timely diagnostic method is required. Detection of microbial volatile organic compounds (VOCs) in exhaled breath is proposed as an alternative method for identifying these pathogens and may distinguish between mono- and poly-microbial infections. Objectives: To investigate volatile metabolites that discriminate between bacterial mono- and co-cultures. Methods: VAP-associated pathogens Enterobacter cloacae and Pseudomonas aeruginosa were cultured individually and together in artificial sputum medium for 24 h and their headspace was analysed for potential discriminatory VOCs by thermal desorption gas chromatography–mass spectrometry. Results: Of the 70 VOCs putatively identified, 23 were found to significantly increase during bacterial culture (i.e. likely to be released during metabolism) and 13 decreased (i.e. likely consumed during metabolism). The other VOCs showed no transformation (similar concentrations observed as in the medium). Bacteria-specific VOCs including 2-methyl-1-propanol, 2-phenylethanol, and 3-methyl-1-butanol were observed in the headspace of axenic cultures of E. cloacae, and methyl 2-ethylhexanoate in the headspace of P. aeruginosa cultures which is novel to this investigation. Previously reported VOCs 1-undecene and pyrrole were also detected. The metabolites 2-methylbutyl acetate and methyl 2-methylbutyrate, which are reported to exhibit antimicrobial activity, were elevated in co-culture only. Conclusion: The observed VOCs were able to differentiate axenic and co-cultures. Validation of these markers in exhaled breath specimens could prove useful for timely pathogen identification and infection type diagnosis.
Ključne besede: Bacteria, Enterobacter cloacae, Gas Chromatography-Mass Spectrometry, Infection, Pseudomonas aeruginosa, Volatile organic compounds
Objavljeno: 18.07.2019; Ogledov: 57; Prenosov: 2
.pdf Polno besedilo (1,29 MB)

33.
Tracer concentration profiles measured in central London as part of the REPARTEE campaign
Damien Martin, K Fredrik Petersson, Iain R White, Stephen H Henshaw, Graham Nickless, Amy Lovelock, Janet F Barlow, Tyrone Dunbar, Curtis R Wood, Dudley E. Shallcross, 2011, izvirni znanstveni članek

Opis: There have been relatively few tracer experiments carried out that have looked at vertical plume spread in urban areas. In this paper we present results from two tracer (cyclic perfluorocarbon) experiments carried out in 2006 and 2007 in central London centred on the BT Tower as part of the REPARTEE (Regent's Park and Tower Environmental Experiment) campaign. The height of the tower gives a unique opportunity to study vertical dispersion profiles and transport times in central London. Vertical gradients are contrasted with the relevant Pasquill stability classes. Estimation of lateral advection and vertical mixing times are made and compared with previous measurements. Data are then compared with a simple operational dispersion model and contrasted with data taken in central London as part of the DAPPLE campaign. This correlates dosage with non-dimensionalised distance from source. Such analyses illustrate the feasibility of the use of these empirical correlations over these prescribed distances in central London.
Ključne besede: advection, concentration (composition), dispersion, tracer, urban atmosphere, vertical mixing, vertical profile
Objavljeno: 18.07.2019; Ogledov: 54; Prenosov: 0
.pdf Polno besedilo (1,49 MB)

34.
Use of reactive tracers to determine ambient OH radical concentrations: Application within the indoor environment
Dudley E. Shallcross, Keven C Clemitshaw, Guy C Lloyd-Jones, Graham Nickless, Stephen J Henshaw, Fredrik K Petersson, Maria Paz Muñoz, Damien Martin, Iain R White, 2010, izvirni znanstveni članek

Opis: The hydroxyl radical (OH) plays a key role in determining indoor air quality. However, its highly reactive nature and low concentration indoors impede direct analysis. This paper describes the techniques used to indirectly quantify indoor OH, including the development of a new method based on the instantaneous release of chemical tracers into the air. This method was used to detect ambient OH in two indoor seminar rooms following tracer detection by gas chromatography- mass spectrometry (GCMS). The results from these tests add to the small number of experiments that have measured indoor OH which are discussed with regard to future directions within air quality research.
Ključne besede: Ozone, Indoor air pollution, Indoor ozone, chemical tracers
Objavljeno: 18.07.2019; Ogledov: 67; Prenosov: 0
.pdf Polno besedilo (153,74 KB)

35.
Headspace volatile organic compounds from bacteria implicated in ventilator-associated pneumonia analysed by TD-GC/MS
Stephen J Fowler, Roy Goodacre, Iain R White, Tamara M E Nijsen, Waqar M Ahmed, Howbeer Muhamadali, Oluwasola Lawal, 2018, izvirni znanstveni članek

Opis: Ventilator-associated pneumonia (VAP) is a healthcare-acquired infection arising from the invasion of the lower respiratory tract by opportunistic pathogens in ventilated patients. The current method of diagnosis requires the culture of an airway sample such as bronchoalveolar lavage, which is invasive to obtain and may take up to seven days to identify a causal pathogen, or indeed rule out infection. While awaiting results, patients are administered empirical antibiotics; risks of this approach include lack of effect on the causal pathogen, contribution to the development of antibiotic resistance and downstream effects such as increased length of intensive care stay, cost, morbidity and mortality. Specific biomarkers which could identify causal pathogens in a timely manner are needed as they would allow judicious use of the most appropriate antimicrobial therapy. Volatile organic compound (VOC) analysis in exhaled breath is proposed as an alternative due to its non-invasive nature and its potential to provide rapid diagnosis at the patient's bedside. VOCs in exhaled breath originate from exogenous, endogenous, as well as microbial sources. To identify potential markers, VAP-associated pathogens Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus were cultured in both artificial sputum medium and nutrient broth, and their headspaces were sampled and analysed for VOCs. Previously reported volatile markers were identified in this study, including indole and 1-undecene, alongside compounds that are novel to this investigation, cyclopentanone and 1-hexanol. We further investigated media components (substrates) to identify those that are essential for indole and cyclopentanone production, with potential implications for understanding microbial metabolism in the lung.
Ključne besede: bacteria, exhaled breath, infection, ventilator-associated pneumonia, volatile organic compounds
Objavljeno: 18.07.2019; Ogledov: 44; Prenosov: 0

36.
Urban tracer dispersion experiments during the second DAPPLE field campaign in London 2004
Damien Martin, Catheryn S Price, Iain R White, Graham Nickless, K Fredrik Petersson, Rex E Britter, Alan G Robins, Stephen E Belcher, Janet F Barlow, Marie Neophytou, Samantha J Arnold, Alan S Tomlin, Robert J Smalley, Dudley E. Shallcross, 2010, izvirni znanstveni članek

Opis: As part of the DAPPLE programme two large scale urban tracer experiments using multiple simultaneous releases of cyclic perfluoroalkanes from fixed location point sources was performed. The receptor concentrations along with relevant meteorological parameters measured are compared with a three screening dispersion models in order to best predict the decay of pollution sources with respect to distance. It is shown here that the simple dispersion models tested here can provide a reasonable upper bound estimate of the maximum concentrations measured with an empirical model derived from field observations and wind tunnel studies providing the best estimate. An indoor receptor was also used to assess indoor concentrations and their pertinence to commonly used evacuation procedures.
Ključne besede: Dapple, dispersion
Objavljeno: 18.07.2019; Ogledov: 65; Prenosov: 0
.pdf Polno besedilo (1,69 MB)

37.
CityFlux perfluorocarbon tracer experiments
Fredrik K Petersson, Damien Martin, Iain R White, Stephen J Henshaw, Graham Nickless, Ian Longley, Carl J Percival, Martin Gallagher, Dudley E. Shallcross, 2010, izvirni znanstveni članek

Opis: In June 2006, two perfluorocarbon tracer experiments were conducted in central Manchester UK as part of the CityFlux campaign. The main aim was to investigate vertical dispersion in an urban area during convective conditions, but dispersion mechanisms within the street network were also studied. Paired receptors were used in most cases where one receptor was located at ground level and one at roof level. One receptor was located on the roof of Portland Tower which is an 80m high building in central Manchester. Source receptor distances in the two experiments varied between 120 and 600 m. The results reveal that maximum concentration was sometimes found at roof level rather than at ground level implying the effectiveness of convective forces on dispersion. The degree of vertical dispersion was found to be dependent on source receptor distance as well as on building height in proximity to the release site. Evidence of flow channelling in a street canyon was also found. Both a Gaussian profile and a street network model were applied and the results show that the urban topography may lead to highly effective flow channelling which therefore may be a very important dispersion mechanism should the right meteorological conditions prevail. The experimental results from this campaign have also been compared with a simple urban dispersion model that was developed during the DAPPLE framework and show good agreement with this. The results presented here are some of the first published regarding vertical dispersion. More tracer experiments are needed in order to further characterise vertical concentration profiles and their dependence on, for instance, atmospheric stability. The impact of urban topography on pollutant dispersion is important to focus on in future tracer experiments in order to improve performance of models as well as for our understanding of the relationship between air quality and public health.
Ključne besede: air quality, atmospheric chemistry, concentration (composition), convective system, dispersion, public health, street canyon, tracer, urban area
Objavljeno: 18.07.2019; Ogledov: 67; Prenosov: 0
.pdf Polno besedilo (1,07 MB)

38.
Distribution of gaseous and particulate organic composition during dark α-pinene ozonolysis
Marie Camredon, Jacqueline F Hamilton, Mohammed S Alam, Kevin P Wyche, Timo Carr, Iain R White, Paul S Monks, Andrew R Rickard, William J Bloss, 2010, izvirni znanstveni članek

Opis: Secondary Organic Aerosol (SOA) affects atmospheric composition, air quality and radiative transfer, however major difficulties are encountered in the development of reliable models for SOA formation. Constraints on processes involved in SOA formation can be obtained by interpreting the speciation and evolution of organics in the gaseous and condensed phase simultaneously. In this study we investigate SOA formation from dark α-pinene ozonolysis with particular emphasis upon the mass distribution of gaseous and particulate organic species. A detailed model for SOA formation is compared with the results from experiments performed in the EUropean PHOtoREactor (EUPHORE) simulation chamber, including on-line gas-phase composition obtained from Chemical-Ionization-Reaction Time-Of-Flight Mass-Spectrometry measurements, and off-line analysis of SOA samples performed by Ion Trap Mass Spectrometry and Liquid Chromatography. The temporal profile of SOA mass concentration is relatively well reproduced by the model. Sensitivity analysis highlights the importance of the choice of vapour pressure estimation method, and the potential influence of condensed phase chemistry. Comparisons of the simulated gaseous-and condensed-phase mass distributions with those observed show a generally good agreement. The simulated speciation has been used to (i) propose a chemical structure for the principal gaseous semi-volatile organic compounds and condensed monomer organic species, (ii) provide evidence for the occurrence of recently suggested radical isomerisation channels not included in the basic model, and (iii) explore the possible contribution of a range of accretion reactions occurring in the condensed phase. We find that oligomer formation through esterification reactions gives the best agreement between the observed and simulated mass spectra
Ključne besede: Aerosol, Aerosol formation, Smog chamber
Objavljeno: 18.07.2019; Ogledov: 59; Prenosov: 0
.pdf Polno besedilo (1,27 MB)

39.
What effect does VOC sampling time have on derived OH reactivity?
Hannah Sonderfeld, Iain R White, Iain C A Goodall, James R Hopkins, Alistair C Lewis, Ralf Koppmann, Paul S Monks, 2016, izvirni znanstveni članek

Opis: State-of-the-art techniques allow for rapid measurements of total OH reactivity. Unknown sinks of OH and oxidation processes in the atmosphere have been attributed to what has been termed ĝ€missingĝ€ OH reactivity. Often overlooked are the differences in timescales over which the diverse measurement techniques operate. Volatile organic compounds (VOCs) acting as sinks of OH are often measured by gas chromatography (GC) methods which provide low-frequency measurements on a timescale of hours, while sampling times are generally only a few minutes. Here, the effect of the sampling time and thus the contribution of unmeasured VOC variability on OH reactivity is investigated. Measurements of VOC mixing ratios by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) conducted during two field campaigns (ClearfLo and PARADE) in an urban and a semi-rural environment were used to calculate OH reactivity. VOCs were selected to represent variability for different compound classes. Data were averaged over different time intervals to simulate lower time resolutions and were then compared to the mean hourly OH reactivity. The results show deviations in the range of 1 to 25%. The observed impact of VOC variability is found to be greater for the semi-rural site.The selected compounds were scaled by the contribution of their compound class to the total OH reactivity from VOCs based on concurrent gas chromatography measurements conducted during the ClearfLo campaign. Prior to being scaled, the variable signal of aromatic compounds results in larger deviations in OH reactivity for short sampling intervals compared to oxygenated VOCs (OVOCs). However, once scaled with their lower share during the ClearfLo campaign, this effect was reduced. No seasonal effect on the OH reactivity distribution across different VOCs was observed at the urban site.
Ključne besede: Hydroxyl radical, Atmospheric chemistry, Box model
Objavljeno: 18.07.2019; Ogledov: 44; Prenosov: 0

40.
Dispersion experiments in central London: The 2007 DAPPLE project
Curtis R Wood, Samantha J Arnold, Ahmed A Balogun, Janet F Barlow, Stephen E Belcher, Rex E Britter, Hong Cheng, Adrian Dobre, Justin J N Lingard, Damien Martin, Marina K Neophytou, Fredrik K Petersson, Alan G Robins, Dudley E. Shallcross, Robert J Smalley, James E Tate, Alison S Tomlin, Iain R White, 2009, izvirni znanstveni članek

Opis: In the event of a release of toxic gas in the center of London, emergency services personnel would need to determine quickly the extent of the area contaminated. The transport of pollutants by turbulent flow within the complex streets and building architecture of London, United Kingdom, is not straightforward, and we might wonder whether it is at all possible to make a scientifically reasoned decision. Here, we describe recent progress from a major U.K. project, Dispersion of Air Pollution and its Penetration into the Local Environment (DAPPLE; information online at www.dapple.org.uk). In DAPPLE, we focus on the movement of airborne pollutants in cities by developing a greater understanding of atmospheric flow and dispersion within urban street networks. In particular, we carried out full-scale dispersion experiments in central London from 2003 through 2008 to address the extent of the dispersion of tracers following their release at street level. These measurements complemented previous studies because 1) our focus was on dispersion within the first kilometer from the source, when most of the material was expected to remain within the street network rather than being mixed into the boundary layer aloft; 2) measurements were made under a wide variety of meteorological conditions; and 3) central London represents a European, rather than North American, city geometry. Interpretation of the results from the full-scale experiments was supported by extensive numerical and wind tunnel modeling, which allowed more detailed analysis under idealized and controlled conditions. In this article, we review the full-scale DAPPLE methodologies and show early results from the analysis of the 2007 field campaign data.
Ključne besede: Air quality, Atmospheric thermodynamics, Dispersions, Experiments
Objavljeno: 18.07.2019; Ogledov: 62; Prenosov: 0
.pdf Polno besedilo (17,86 MB)

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