Centre for Research into Atmospheric Chemistry - Doctoral Theses
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Item New tools and methods for analysis of the sources and spatial distribution of air pollution(University College Cork, 2024) Byrne, Rósín; Hellebust, Stig; Wenger, John; Environmental Protection Agency; European CommissionRecent improvements in air quality sensors (AQSs) have presented an affordable and scalable way to enhance air quality monitoring. However, fully exploiting these new data sources requires novel data-driven methodologies to address the inherent uncertainties in the measurements reported by AQSs. This work goes beyond calibration exercises to highlight the potential of AQS networks for air quality assessments, particularly after demonstrating good sensor-reference correlations and minimal inter-sensor variation. Using three distinct datasets from AQS networks in Cork City and Dungarvan, Ireland, a range of analytical approaches have been developed and applied to understand the local spatiotemporal variability of PM2.5 in these urban areas. A novel method leveraging high temporal resolution data from PurpleAir sensors linked rapid, short-lived concentration fluctuations to local emissions. The analysis revealed stark spatial contrasts in the proportion of local emissions across Cork City. On average, half of the total PM2.5 exposure originated mainly from local emissions and occurred in just 30% of the time. Discrete Fourier transform spectral analysis was also used to estimate local PM2.5 contributions, yielding comparable results when applied to the same dataset. Analysis of the temporal changes to the contribution of local emissions in Cork City between 2021 and 2023 suggested that legislative changes may be positively influencing the proportion of locally emitted PM2.5 in winter, however, this effect is not uniform across the city. A new metric, the concentration similarity index (CSI), was developed and optimised for AQS network data. The CSI was used to assess the spatial representativeness of Environmental Protection Agency (EPA) monitoring locations in both Dungarvan and Cork City, revealing moderate exposure representation. However, significant spatial variability within each sensor network indicated strong differences in the degree of representation by the central monitoring locations and emphasised that location type, rather than geographical proximity, plays a key role in air quality representation. Additionally, a frequency-based method was integrated with the analysis of winter EPA PM2.5 data and aethalometer-derived equivalent black carbon (eBC) data in a small Irish town, to investigate the changing impact of local emissions over time. Analysis of data from 2018 to 2024 showed considerable reductions in winter pollution levels, suggesting an overall improvement in air quality in the area. Analysis of the Ångström absorption exponent indicated an evolving emissions profile, with an increase in wood or peat/turf burning in recent years, while spectral analysis showed general reductions in both regional/background and local particulate pollution. This research offers insight into cost-effective, spatially dense air quality monitoring solutions that can inform vital pollution mitigation strategies. The new methodologies developed across all datasets, demonstrate the potential for integrating AQS networks and data-driven techniques into air quality monitoring and assessment.Item 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 CouncilBiomass 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.Item The emission and atmospheric oxidation of biogenic volatile organic compounds from Sitka spruce(University College Cork, 2023) Furnell, Hayley; Wenger, John; Hellebust, Stig; Irish Research Council; Environmental Protection AgencyBiogenic volatile organic compounds (BVOCs) emitted by plants undergo chemical reactions in the atmosphere resulting in the formation of oxidised products and secondary organic aerosols (SOA), which have a large impact on climate. In this work an on-line time-of-flight chemical ionisation mass spectrometer (ToF-CIMS) was used in laboratory studies to identify the main BVOCs emitted from the main plantation tree species in Ireland, Picea Sitchensis (Sitka spruce). Experiments have also been conducted to assess the atmospheric oxidation pathways of the BVOCs emitted by Sitka spruce and their SOA formation potential. The ToF-CIMS was used in combination with off-line gas chromatography-mass spectrometry to identify the BVOC emissions from three Sitka spruce trees maintained in a plant growth chamber under conditions relevant to the Irish climate. Fifty-two of the seventy-four BVOCs emitted from Sitka spruce were oxygenated compounds, with piperitone (C10H16O), an oxygenated monoterpene, being the dominant emission. Other prevalent emissions included isoprene and five monoterpenes (myrcene, β-phellandrene, δ-limonene, α-pinene, and camphene). Temperature, light intensity and stress were all found to alter the emission profiles, with different BVOCs exhibiting different responses. At the current conditions of the Irish climate the annual BVOC flux for isoprene was found to exceed that for piperitone, although this is expected to change in a warming climate. A series of simulation chamber experiments was performed to determine, for the first time, the kinetics, products and mechanisms for the gas-phase reaction of piperitone with the main atmospheric oxidant the hydroxyl radical (OH•). The rate coefficient was determined by the relative rate method and used to calculate an atmospheric lifetime of under 2 hours. Calculations based on structure activity relationships identified the reaction with OH• as the dominant loss pathway for piperitone and was used to identify its most reactive sites. The ToF-CIMS detected thirty-three gas-phase oxidation products, and formation mechanisms for seventeen of the products have been proposed. The results from these experiments provide new and useful information on the atmospheric fate of piperitone. Oxidation experiments were also conducted with OH• on all the BVOCs emitted by a Sitka spruce tree, to identify oxidation products, reaction pathways and determine the SOA formation potential of whole Sitka spruce BVOC emissions. Eight gas-phase BVOCs were identified as key reactive emissions, and upon reaction with OH• led to the formation of twenty-five gas-phase products and ninety-nine particle-phase products. Eight of these products were identified as originating from the oxidation of piperitone, myrcene and isoprene across the gas-phase and particle-phase, with the majority of the remining products resulting from oligomerisation reactions. Rapid SOA formation was observed soon after the onset of oxidation, likely due to the formation of low volatility oxidation products which caused new particle formation. SOA yields were estimated to be around 15%. Overall, this work has produced a wealth of new information on the emission and atmospheric oxidation of BVOCs emitted from Sitka spruce, which will be valuable to decision makers in the forestry sector. Moreover, the research highlights the importance of assessing BVOC emissions and the associated SOA formation potential prior to establishing tree plantations.Item Spatial and temporal variation of ambient carbonaceous aerosol in Ireland and strategies for effective monitoring of source contributions(University College Cork, 2022-04) Heffernan, Eimear; Hellebust, Stig; University College Cork; Environmental Protection Agency; European CommissionThe concentration, size and composition of atmospheric aerosols determines their impact on health and climate. These parameters are highly variable and inherently linked with source, seasonality and geographical location. In this study, a suite of instruments was deployed to quantitatively investigate the properties of ambient carbonaceous aerosol at six unique locations around Ireland. Source apportionment analysis was performed for the identification of dominant sources contributing to the ambient carbonaceous aerosol in each environment. This work serves to highlight the spatial and temporal variability of ambient carbonaceous aerosol in Ireland. Aethalometer data exhibited significant spatial variability of black carbon (BC). The lowest concentrations were recorded at regional background sites, while the highest concentrations were recorded in populous, urban settings. The aethalometer source apportionment model was used to demonstrate spatial variability of contributions from dominant sources. The temporal variability of carbonaceous aerosol was explored through data collected during long-term monitoring campaigns in Dublin and Enniscorthy. Strong seasonal variation in equivalent black carbon (eBC) was evident, particularly in locations strongly influenced by solid fuel burning for residential heating. Furthermore, approximately 40% and 72% of total eBC measured during winter at University College Dublin and Enniscorthy, respectively, was attributed to solid fuel combustion. Strong diurnal trends were observed in each location, however the absolute concentration was seasonally dependent. A pronounced evening peak, attributed to solid fuel combustion emissions, was observed at the majority of sampling sites during the winter months. Urban areas also had a morning peak consistent with rush hour and was attributed to the influence of traffic-related emissions. Novel data collected at several unique environments as part of three individual long-term monitoring campaigns, demonstrated the ubiquitous nature of carbonaceous aerosol, particularly BC, in Ireland and the associated impact on local air quality. Despite the negative implications on human health, air quality and climate, BC is not regulated or routinely monitored in Ireland. This research outlines the potential benefits of establishing an extensive, national BC monitoring network, including the collection of real-time data to inform vital air pollution mitigation policies.Item 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 CouncilBlack 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.