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41.
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: 64; Prenosov: 0
.pdf Polno besedilo (1,27 MB)

42.
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: 48; Prenosov: 0

43.
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: 67; Prenosov: 0
.pdf Polno besedilo (17,86 MB)

44.
Year-long measurements of C1-C3 halocarbons at an urban site and their relationship with meteorological parameters
Dudley E Shallcross, Brian G R Greally, Alison C Rivett, Damien Martin, Alan Knights, Graham Nickless, Ben Golledge, Iain R White, M Iqbal Mead, M Anwar K Khan, 2009, izvirni znanstveni članek

Opis: The mixing ratios of 11 C1–C3 halocarbons have been measured using a GC–twin‐linked ECD system over the period from October 2004 to December 2005 at an urban site in Bristol, UK. Time series and seasonal variations of the halocarbons were analysed over the period to determine biogenic and anthropogenic sources and sinks. Correlations between the target halocarbons were also observed, suggesting common sources within the area. Wind rose plots for all halocarbons have been used to assist in the determination of halocarbons sources. Halocarbon concentrations are highest at low‐wind speeds and decrease as wind speed increases, a few species (CCl4 and CH3Cl most notably) rise at very high‐wind speeds suggesting release from the Bristol Channel.
Ključne besede: adsorption–desorption system, anthropogenic halocarbons, biogenic halocarbons, electron capture detector, gas chromatography, methyl bromide
Objavljeno: 18.07.2019; Ogledov: 69; Prenosov: 0
.pdf Polno besedilo (897,06 KB)

45.
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.
Ključne besede: dapple, perfluorocarbon, tracer, mobile source
Objavljeno: 18.07.2019; Ogledov: 80; Prenosov: 0
.pdf Polno besedilo (265,68 KB)

46.
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.
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: 94; Prenosov: 0
.pdf Polno besedilo (227,35 KB)

47.
48.
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.
Ključne besede: Africa, Biofuel, Domestic biomass burning, Emission factor, Methyl halide
Objavljeno: 17.07.2019; Ogledov: 86; Prenosov: 0
.pdf Polno besedilo (781,64 KB)

49.
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.
Ključne besede: dispersion, tracer, intermittency
Objavljeno: 17.07.2019; Ogledov: 83; Prenosov: 4
.pdf Polno besedilo (289,67 KB)

50.
An estimation of the global emission of methyl bromide from rapeseed (Brassica napus) from 1961 to 2003
2008, izvirni znanstveni članek

Opis: Gan et al. [Gan, J., Yates, S.R., Ohr, H.D., Sims, J.J., 1998. Production of methyl bromide by terrestrial higher plants. Geophysical Research Letters 25 (19), 3595–3598] have reported that plants of the family Brassicaceae take up bromide from soils and subsequently release methyl bromide (CH3Br) to the atmosphere deriving a significant emission from this source of about 7 Gg(109 g) yr−1. In this study, we determine a yearly global emission rate for CH3Br from one such species, rapeseed, from 1961 to 2003 using data on crop harvest index and growth rate in conjunction with global production data. This study suggests that CH3Br emissions from rapeseed have increased 10-fold from 1961 to 2003 and by a factor of 3–4 since 1980. It also suggests that the geographical distribution of emissions has also changed substantially in the last 40 yr. The annual emission of CH3Br from mustard and cabbage is also estimated; whilst relative levels emitted from these species are less significant, as these crops are continually exploited for new applications CH3Br emissions are set to increase.
Ključne besede: CH3Br, Rapeseed, Brassica, Ozone, Biosphere
Objavljeno: 17.07.2019; Ogledov: 56; Prenosov: 0
.pdf Polno besedilo (574,91 KB)

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