Browsing by Author "Shallcross, D.E"

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    Chemical characterisation of benzene oxidation products under high- And low-NOx conditions using chemical ionisation mass spectrometry
    (Copernicus GmbH, 2021) Shallcross, D.E; Priestley, M; Bannan, T.J
    Aromatic hydrocarbons are a class of volatile organic compounds associated with anthropogenic activity and make up a significant fraction of urban volatile organic compound (VOC) emissions that contribute to the formation of secondary organic aerosol (SOA). Benzene is one of the most abundant species emitted from vehicles, biomass burning and industry. An iodide time-of-flight chemical ionisation mass spectrometer (ToF-CIMS) and nitrate ToF-CIMS were deployed at the Jülich Plant Atmosphere Chamber as part of a series of experiments examining benzene oxidation by OH under high- and low-NOx conditions, where a range of organic oxidation products were detected. The nitrate scheme detects many oxidation products with high masses, ranging from intermediate volatile organic compounds (IVOCs) to extremely low volatile organic compounds (ELVOCs), including C12 dimers. In comparison, very few species with C≥6 and O≥8 were detected with the iodide scheme, which detected many more IVOCs and semi-volatile organic compounds (SVOCs) but very few ELVOCs and low volatile organic compounds (LVOCs). A total of 132 and 195 CHO and CHON oxidation products are detected by the iodide ToF-CIMS in the low- and high-NOx experiments respectively. Ring-breaking products make up the dominant fraction of detected signal and 21 and 26 of the products listed in the Master Chemical Mechanism (MCM) were detected. The time series of highly oxidised (O≥6) and ring-retaining oxidation products (C6 and double-bond equivalentD4) equilibrate quickly, characterised by a square form profile, compared to MCM and ring-breaking products which increase throughout oxidation, exhibiting sawtooth profiles. Under low-NOx conditions, all CHO formulae attributed to radical termination reactions of first-generation benzene products, and first-generation auto-oxidation products are observed.
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    Intercomparison of the representations of the atmospheric chemistry of pre-industrial methane and ozone in earth system and other global chemistry-transport models
    (Elsevier, 2021) Shallcross, D.E; Derwent, R.G; Parrish, D.D
    An intercomparison has been set up to study the representation of the atmospheric chemistry of the pre-industrial troposphere in earth system and other global tropospheric chemistry-transport models. The intercomparison employed a constrained box model and utilised tropospheric trace gas composition data for the pre-industrial times at ninety mid-latitude surface locations. Incremental additions of four organic compounds: methane, ethane, acetone and propane, were used to perturb the constrained box model and generate responses in hydroxyl radicals and tropospheric ozone at each location and with each chemical mechanism. Although the responses agreed well across the chemical mechanisms from the selected earth system and other global tropospheric chemistry-transport models, there were differences in the detailed responses between the chemical mechanisms that could be tracked down by sensitivity analysis to differences in the representation of C1–C3 chemistry. Inter-mechanism ranges in NOx compensation points were about 0.17 ± 0.12 when expressed relative to the inter-mechanism average. Monte Carlo uncertainty analysis carried out with a single chemical mechanism put the intra-mechanism range a factor of three higher at 0.50 ± 0.12.
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    Investigating the background and local contribution of the oxidants in London and Bangkok
    (Royal Society of Chemistry, 2021) Shallcross, D.E; Khan, M.A.H; Holland, R
    Birth registration marks a child’s right to identity and is the first step to establishing citizenship and access to services. At the population level, birth registration data can inform effective programming and planning. In Tanzania, almost two-thirds of births are in health facilities, yet only 26% of children under 5 years have their births registered. Our mixed-methods research explores the gap between hospital birth and birth registration in Dar es Salaam, Tanzania. Methods: The study was conducted in the two Tanzanian hospital sites of the Every Newborn-Birth Indicators Research Tracking in Hospitals (EN-BIRTH) multi-country study (July 2017–2018). We described the business processes for birth notification and registration and collected quantitative data from women’s exit surveys after giving birth (n = 8038). We conducted in-depth interviews (n = 21) to identify barriers and enablers to birth registration among four groups of participants: women who recently gave birth, women waiting for a birth certificate at Temeke Hospital, hospital employees, and stakeholders involved in the national birth registration process. We synthesized findings to identify opportunities to improve birth registration.
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    Tropospheric modeling of acetic acid in the UK for summer, winter and spring seasons using a mesoscale 3-dimensional chemistry and transport model, WRF-Chem-CRI
    (Elsevier, 2021) Shallcross, D.E; Khan, M.A.H; Dennis, J.W
    The measurement of acetic acid during the ClearfLo campaign for Winter 2012 and Summer 2012 in London and at the Weybourne Research Station (East Anglia), UK for Spring 2013 gives the average ± 1σ mixing ratios of 45.9 ± 31.5, 25.7 ± 14.3 and 55.1 ± 32.0 ppt, respectively. The WRF-Chem-CRI model was run over these three seasons and within uncertainty reproduced the data from London, with mixing ratios during Winter (32.3 ± 25.3 ppt) and Summer (55.1 ± 22.6 ppt). The model's seasonality was opposite to that observed and although within the combined uncertainty of the measurement and model data it underpredicted the levels observed at Weybourne during Spring (28.9 ± 19.3 ppt). The model-measurement correlations of the meteorological parameters (e.g. temperature, wind direction, wind speed) were good with a correlation of R > 0.7. The predicted diurnal trend of acetic acid resembled measurement data with a small negative bias during winter but performed less well during summer with a large positive bias and in spring with a large negative bias. The reasonable correlation of acetic acid mixing ratios with temperature was found to be similar for both measurement and model (Rmeasurement = 0.5, Rmodel = 0.6) during Summer suggesting the importance of the photochemical secondary source of acetic acid which was reflected both in the measurement and the model. The key processes identified from the model results were a) missing direct anthropogenic sources of acetic acid (accounting for the lower model winter values) and b) not including its loss process by Criegee intermediates (accounting for the higher model values in summer). Comparing the weekend data with weekday data revealed a likely underpredicted source of acetic acid from vehicles. The wet deposition removal process of acetic acid was found not to be as significant in the UK as anticipated.