Iain R. White

DISPERSION EXPERIMENTS IN CENTRAL LONDON The 2007 Dapple Project

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...

Increased sensitivity in proton transfer reaction mass spectrometry by incorporation of a radio frequency ion funnel.

A drift tube capable of simultaneously functioning as an ion funnel is demonstrated in proton transfer reaction mass spectrometry (PTR-MS) for the first time. The ion funnel enables a much higher proportion of ions to exit the drift tube and enter the mass spectrometer than would otherwise be the case. An increase in the detection sensitivity for volatile organic compounds of between 1 and 2 orders of magnitude is delivered, as demonstrated using several compounds. Other aspects of analytical performance explored in this study include the effective E/N (ratio of electric field to number density of the gas) and dynamic range over which the drift tube is operated. The dual-purpose drift tube/ion funnel can be coupled to various types of mass spectrometers to increase the detection sensitivity and may therefore offer considerable benefits in PTR-MS work.

Use of Reactive Tracers To Determine Ambient OH Radical Concentrations: Application within the Indoor Environment

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.

Real-time multi-marker measurement of organic compounds in human breath : towards fingerprinting breath.

The prospects for exploiting proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS) in medical diagnostics are illustrated through a series of case studies. Measurements of acetone levels in the breath of 68 healthy people are presented along with a longitudinal study of a single person over a period of 1 month. The median acetone concentration across the population was 484 ppbV with a geometric standard deviation (GSD) of 1.6, whilst the average GSD during the single subject longtitudinal study was 1.5. An additional case study is presented which highlights the potential of PTR-ToF-MS in pharmacokinetic studies, based upon the analysis of online breath samples of a person following the consumption of ethanol. PTR-ToF-MS comes into its own when information across a wide mass range is required, particularly when such information must be gathered in a short time during a breathing cycle. To illustrate this property, multicomponent breath analysis in a small study of cystic fibrosis patients is detailed, which provides tentative evidence that online PTR-ToF-MS analysis of tidal breath can distinguish between active infection and non-infected patients.

Stable carbon isotope analysis of selected halocarbons at parts per trillion concentration in an urban location

Environmental Context. Halocarbons can have significant effects on the atmosphere and the environment, particularly with regard to ozone depletion and climate change impacts. The determination of isotopic concentrations for selected halocarbon species should provide useful information to identify and constrain halocarbon sources and sinks within the urban environment. In the present study, a new instrumental method is described to determine these isotope ratios for selected halocarbons and the resultant data are interpreted in terms of local sources and sinks. Abstract. δ13C 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 Chromatography–Combustion–Isotope Ratio Mass Spectrometer was used to determine δ13C 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 δ13C values for selected halocarbons from different areas in the present study suggests that δ13C values may be used to determine the relative magnitudes of anthropogenic and biogenic sources.

Metabolite profiling of the ripening of Mangoes Mangifera indica L. cv. 'Tommy Atkins' by real-time measurement of volatile organic compounds.

Real-time profiling of mango ripening based on proton transfer reaction-time of flight-mass spectrometry (PTR–ToF–MS) of small molecular weight volatile organic compounds (VOCs), is demonstrated using headspace measurements of ‘Tommy Atkins’ mangoes. VOC metabolites produced during the ripening process were sampled directly, which enabled simultaneous and rapid detection of a wide range of compounds. Headspace measurements of ‘Keitt’ mangoes were also conducted for comparison. A principle component analysis of the results indicated that several mass channels were not only key to the ripening process but could also be used to distinguish between mango cultivars. The identities of 22 of these channels, tentatively speciated using contemporaneous GC–MS measurements of sorbent tubes, are rationalized through examination of the biochemical pathways that produce volatile flavour components. Results are discussed with relevance to the potential of headspace analysers and electronic noses in future fruit ripening and quality studies.

CityFlux perfluorocarbon tracer experiments

CityFlux perfluorocarbon tracer experiments F. K. Petersson, D. Martin, I. R. White, S. J. Henshaw, G. Nickless, I. Longley, C. J. Percival, M. Gallagher, and D. E. Shallcross School of Chemistry, University of Bristol, Bristol, UK SEAS, University of Manchester, Manchester, UK now at: Ionicon Analytik Gesellschaft m.b.H., Innsbruck, Austria now at: National Institute of Water and Atmospheric Research, New Zealand Received: 30 September 2009 – Accepted: 3 December 2009 – Published: 5 January 2010 Correspondence to: D. E. Shallcross (d.e.shallcross@bristol.ac.uk) Published by Copernicus Publications on behalf of the European Geosciences Union.