Centre for Research into Atmospheric Chemistry - Doctoral Theses

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    Field measurements and atmospheric simulation chamber studies of selected biomass burning marker compounds
    (University College Cork, 2023) O'Sullivan, Niall Patrick; Wenger, John; Environmental Protection Agency; Irish Research Council
    Biomass burning is a key contributor to ambient air pollution, which has significant impacts on climate and health. Biomass burning emits both solid particles and gaseous species known as volatile organic compounds (VOCs) which can undergo chemical oxidation reactions in the atmosphere with hydroxyl (OH) and nitrate (NO3) radicals to produce secondary organic aerosols (SOA). While the particulate pollution has been well characterised, information on the VOCs associated with biomass burning is limited. To this end, a Time-of-Flight Chemical Ionisation Mass Spectrometer (ToF-CIMS) was deployed in Cork City, for the first comprehensive field study on the VOCs associated with residential burning of solid fuels (wood, peat, coal) in Ireland. In the field study, a range of phenols and their nitro derivatives were detected during air pollution events caused by residential solid fuel burning. By following the evolution of these biomass burning markers through the night, evidence was found for the atmospheric conversion of phenol compounds to their analogous nitrophenols via gas-phase reaction with NO 3 . Positive matrix factorisation was used to identify six different source categories for the VOCs which included fresh and atmospherically processed emissions from solid fuel burning, as well as oxidized emissions from local and regional background sources such as vehicles and agriculture. A series of simulation chamber studies was also performed on the OH-initiated oxidation of two biomass burning marker compounds, 4-methylcatechol and guaiacol. The ToF-CIMS identified a large range of gas and particle products including polyphenols, nitrophenols, benzoquinones, ring scission species and accretion products, generating new information on the atmospheric degradation pathways. The results confirm the importance of both OH addition and H-atom abstraction reactions in initiating the oxidation processes and interestingly, in the case of guaiacol, loss of the methoxy group to form catechol which also underwent similar degradation pathways. A wide range of highly oxidized and nitro-containing species were identified in the particle phase which experienced further chemical processing, thus providing new insights into the mechanisms for the formation and atmospheric aging of SOA produced from biomass burning.
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    Nature and origin of black carbon in Ireland
    (University College Cork, 2019-12) Buckley, Paul; Wenger, John; Sodeau, John R.; Environmental Protection Agency; Irish Research Council
    Black carbon (BC) particles are important atmospheric radiative forcing agents and also have a negative effect on human health. In this study, a seven wavelength, dual spot aethalometer, was used to determine the equivalent BC (eBC) concentrations at four locations in Ireland; Killarney, Enniscorthy, Birr and Dublin. The aethalometer data were combined with other measurements and meteorological parameters to determine the sources of the particles observed at the monitoring sites. The mean eBC concentrations measured in Killarney and Enniscorthy were higher than those in Dublin during the winter months, while the concentrations in Birr were only marginally lower. The aethalometer source apportionment model was used to show that domestic solid fuel burning accounted for 61%, 81% and 63% of eBC mass in Killarney, Enniscorthy and Birr respectively. The average diurnal profiles for eBC at these three locations showed a minor peak during morning hours attributed to traffic and a very large peak during the evening due to solid fuel burning. Results from two years of continuous measurements at an urban background location in Dublin, showed a strong seasonal variation in eBC. Higher concentrations were measured during winter due to solid fuel burning, which accounted for 57% of eBC during the winter of 2016/2017, and 50% during the winter of 2017/2018. The diurnal profile for Dublin during winter was similar to that observed at the other three sites. During summer, eBC levels were much lower and dominated by traffic emissions. The parameters used in the source apportionment model were explored and site-specific absorption Ångström exponents (α) and Mass Absorption Cross-section (MAC) values were also derived to provide an indication of the different aerosol properties at each location. The results of the source apportionment at all four sites correlate strongly with those from other instruments deployed during the campaigns. The BC levels recorded in Dublin were compared to historical measurements of black smoke in Dublin, Belfast, London and Paris, from 1963 to 2003. Large decreases in BS concentrations (over 90%) have been observed in each city and are related to legislative changes introduced in each jurisdiction over the decades. Overall, this work has highlighted the ability of the aethalometer to measure eBC concentrations in real-time and derive contributions from both solid fuel burning and traffic emissions.