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1.
Trace detection of C2H2 in ambient air using continuous wave cavity ring-down spectroscopy combined with sample pre-concentration
Orr-Ewing Andrew, Damien Martin, Iain White, Roberto Grilli, Ruth Lindley, Manik Pradhan, 2008, izvirni znanstveni članek

Opis: Continuous wave cavity ring-down spectroscopy (cw-CRDS) coupled with sample pre-concentration has been used to measure acetylene (C2H2) mixing ratios in ambient air. Measurements were made in the near-infrared region (λ∼1535.393 nm), using the P(17) rotational line of the (ν1+ν3) vibrational combination band, a region free from interference by overlapping spectral absorption features of other air constituents. The spectrometer is shown to be capable of fast, quantitative and precise C2H2 mixing ratio determinations without the need for gas chromatographic (GC) separation. The current detection limit of the spectrometer following sample pre-concentration is estimated to be 35 parts per trillion by volume (pptv), which is sufficient for direct atmospheric detection of C2H2 at concentrations typical of both urban and rural environments. The CRDS apparatus performance was compared with an instrument using GC separation and flame ionization detection (GC-FID); both techniques were used to analyze air samples collected within and outside the laboratory. These measurements were shown to be in quantitative agreement. The indoor air sample was found to contain C2H2 at a mixing ratio of 3.87±0.22 ppbv (3.90±0.23 ppbv by GC-FID), and the C2H2 fractions in the outside air samples collected on two separate days from urban locations were 1.83±0.20 and 0.69±0.14 ppbv (1.18±0.09 and 0.60±0.04 ppbv by GC-FID). The discrepancy in the first outdoor air sample is attributed to degradation over a 2-month interval between the cw-CRDS and GC-FID analyses.
Najdeno v: osebi
Ključne besede: Rotational Line, Cavity Enhance Absorption Spectroscopy, Adsorbent Trap, Trace Atmospheric Constituent, CRDS Instrument
Objavljeno: 15.07.2019; Ogledov: 251; Prenosov: 0
.pdf Polno besedilo (363,50 KB)

2.
Circadian rhythm of exhaled biomarkers in health and asthma
Stephen Fowler, Royston Goodacre, David Ray, Dave Singh, Iain White, John Blaikley, Andrew Loudon, Robert Maidstone, Max Wilkinson, Hannah Durrington, 2019, izvirni znanstveni članek

Opis: Circadian rhythms control many biological processes in the body in both health and disease. Greater understanding of diurnal variability in disease related biomarkers is crucial for their application in clinical practice and biomarkers of circadian rhythm are required to facilitate further research into disturbed chronicity. To determine if fractional exhaled nitric oxide and breath volatile biomarkers vary rhythmically during the day in healthy and asthmatic individuals. Ten individuals with moderate, atopic asthma (on regular inhaled corticosteroids) and 10 healthy volunteers (all non-smokers) completed an overnight visit where their exhaled breath volatiles and forced exhaled nitric oxide levels were collected every 6 h. Breath volatiles were analysed using gas chromatography mass spectrometry, after trapping these volatiles on sorbent materials for thermal desorption. Nine breath volatiles (including acetone and isoprene) exhibit diurnal variation across all individuals. Furthermore the circadian pattern of several VOCs is altered in individuals with asthma and fractional exhaled nitric oxide is rhythmic in asthma but not in healthy controls. Markers of circadian rhythm can be identified in breath and may offer insight into circadian profiling to help treat disease. Additionally this work suggests that time of day must be controlled when designing future biomarker discovery studies. Further work is required with larger cohorts to validate and extend these findings.
Najdeno v: osebi
Ključne besede: VOCs, breath, asthma, circadian
Objavljeno: 21.10.2019; Ogledov: 158; Prenosov: 0
.pdf Polno besedilo (479,14 KB)

3.
Metabolic dysregulation in vitamin E and carnitine shuttle energy mechanisms associate with human frailty
James Nazroo, Royston Goodacre, Neil Pendleton, Frederick Wu, Iain White, Bram Vanhoutte, Gindo Tampubolon, Alan Marshall, Krisztina Mekli, Zahra Rattray, Tarani Chandola, Caroline Johnson, Drupad Trivedi, Yun Xu, Nicholas Rattray, 2019, izvirni znanstveni članek

Opis: Global ageing poses a substantial economic burden on health and social care costs. Enabling a greater proportion of older people to stay healthy for longer is key to the future sustainability of health, social and economic policy. Frailty and associated decrease in resilience plays a central role in poor health in later life. In this study, we present a population level assessment of the metabolic phenotype associated with frailty. Analysis of serum from 1191 older individuals (aged between 56 and 84 years old) and subsequent longitudinal validation (on 786 subjects) was carried out using liquid and gas chromatography-mass spectrometry metabolomics and stratified across a frailty index designed to quantitatively summarize vulnerability. Through multivariate regression and network modelling and mROC modeling we identified 12 significant metabolites (including three tocotrienols and six carnitines) that differentiate frail and non-frail phenotypes. Our study provides evidence that the dysregulation of carnitine shuttle and vitamin E pathways play a role in the risk of frailty.
Najdeno v: osebi
Ključne besede: metabolomics, frailty, ageing, LC-MS, serum
Objavljeno: 08.11.2019; Ogledov: 132; Prenosov: 3
.pdf Polno besedilo (2,35 MB)

4.
A study of pollutant concentration variability in an urban street under low wind speeds
Adrian Dobre, Graham Nickless, Iain R White, Catheryn S Price, Damien Martin, Dudley E Shallcross, 2008, izvirni znanstveni članek

Opis: The short time‐scale variability in pollutant concentrations in an urban street under very low wind speed conditions and short source–receptor distance has been investigated using the inert tracer sulfur hexafluoride (SF6) as a continuous point‐source (release times ≥ 5 min), and fast detection using separation by gas chromatography coupled with a μ‐electron capture detector (ECD). The results are complex but can be broadly interpreted in terms of horizontal wind speed and direction coherence. Comparisons with a simple dispersion model suggest that observed time‐averaged maximum concentrations approach predicted values, whilst instantaneous maximum concentrations vary greatly and would therefore be difficult to predict.
Najdeno v: osebi
Ključne besede: dispersion, tracer, intermittency
Objavljeno: 17.07.2019; Ogledov: 238; Prenosov: 12
.pdf Polno besedilo (289,67 KB)

5.
Methyl halide emission estimates from domestic biomass burning in Africa
M Iqbal Mead, M Anwar H Khan, Iain R White, Graham Nicless, Dudley E Shallcross, 2008, izvirni znanstveni članek

Opis: Inventories of methyl halide emissions from domestic burning of biomass in Africa, from 1950 to the present day and projected to 2030, have been constructed. By combining emission factors from Andreae and Merlet [2001. Emission of trace gases and aerosols from biomass burning. Global Biogeochemical Cycles 15, 955-966], the biomass burning estimates from Yevich and Logan [2003. An assessment of biofuel use and burning of agricultural waste in the developing world. Global Biogeochemical Cycles 17(4), 1095, doi:10.1029/2002GB001952] and the population data from the UN population division, the emission of methyl halides from domestic biomass usage in Africa has been estimated. Data from this study suggest that methyl halide emissions from domestic biomass burning have increased by a factor of 4-5 from 1950 to 2005 and based on the expected population growth could double over the next 25 years. This estimated change has a non-negligible impact on the atmospheric budgets of methyl halides.
Najdeno v: osebi
Ključne besede: Africa, Biofuel, Domestic biomass burning, Emission factor, Methyl halide
Objavljeno: 17.07.2019; Ogledov: 236; Prenosov: 0
.pdf Polno besedilo (781,64 KB)

6.
Stable carbon isotope analysis of selected halocarbons at parts per trillion concentration in an urban location
M Iqbal Mead, M Anwar H Khan, Ian D Bull, Iain R White, Graham Nickless, Dudley E Shallcross, 2008, izvirni znanstveni članek

Opis: ∂13C values of a suite of halocarbons have been determined in an urban background site in Bristol, UK. A novel mobile preconcentration system, based on the use of multi-adsorbent sample tubes, has been developed for trapping relatively large-volume air samples in potentially remote areas. An Adsorption Desorption System-Gas Chromatography-Electron Capture Detector was used to measure the mixing ratios of the selected halocarbon species, while a Gas ChromatographyCombustionIsotope Ratio Mass Spectrometer was used to determine ∂13C values. For the species with strong local sources, the variation of isotope ratios has been observed over the experimental period. Some of the results reported in the present study differ from previously reported values and reasons for this are discussed. The reporting of different ∂13C values for selected halocarbons from different areas in the present study suggests that ∂13C values may be used to determine the relative magnitudes of anthropogenic and biogenic sources.
Najdeno v: osebi
Ključne besede: Adsorption Desorption System (ADS), Automated Thermal Desorber (ATD), Electron Capture Detector (ECD), Gas Chromatography (GC), Isotope Ratio Mass Spectrometry (IRMS)
Objavljeno: 18.07.2019; Ogledov: 224; Prenosov: 0
.pdf Polno besedilo (227,35 KB)

7.
Short-range urban dispersion experiments using fixed and moving sources
Stephen E Belcher, Alison S Tomlin, James Tate, Marina K Neophytou, Rex E Britter, Fredrik Petterson, Iain R White, Graham Nickless, Catheryn S Price, Damien Martin, Dudley E. Shallcross, Janet F Barlow, Alan Robins, 2009, izvirni znanstveni članek

Opis: Four perfluorocarbon tracer dispersion experiments were carried out in central London, United Kingdom in 2004. These experiments were supplementary to the dispersion of air pollution and penetration into the local environment (DAPPLE) campaign and consisted of ground level releases, roof level releases and mobile releases; the latter are believed to be the first such experiments to be undertaken. A detailed description of the experiments including release, sampling, analysis and wind observations is given. The characteristics of dispersion from the fixed and mobile sources are discussed and contrasted, in particular, the decay in concentration levels away from the source location and the additional variability that results from the non-uniformity of vehicle speed.
Najdeno v: osebi
Ključne besede: dapple, perfluorocarbon, tracer, mobile source
Objavljeno: 18.07.2019; Ogledov: 210; Prenosov: 0
.pdf Polno besedilo (265,68 KB)

8.
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.
Najdeno v: osebi
Ključne besede: Air quality, Atmospheric thermodynamics, Dispersions, Experiments
Objavljeno: 18.07.2019; Ogledov: 207; Prenosov: 0
.pdf Polno besedilo (17,86 MB)

9.
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
Najdeno v: osebi
Ključne besede: Aerosol, Aerosol formation, Smog chamber
Objavljeno: 18.07.2019; Ogledov: 189; Prenosov: 0
.pdf Polno besedilo (1,27 MB)

10.
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.
Najdeno v: osebi
Ključne besede: air quality, atmospheric chemistry, concentration (composition), convective system, dispersion, public health, street canyon, tracer, urban area
Objavljeno: 18.07.2019; Ogledov: 217; Prenosov: 0
.pdf Polno besedilo (1,07 MB)

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