Centre for Research into Atmospheric Chemistry - Doctoral Theses

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    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 Commission
    The 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.
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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.
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    Real-time bioaerosol analysis in the healthcare environment
    (University College Cork, 2020-01) Fennelly, Mehael; Sodeau, John R.; Prentice, Michael B.; O’Connor, David; Healthcare Infection Society
    Airborne infection has been difficult to study in hospitals. Conventional sampling methods for airborne organisms are limited in sample time intervals (minutes to hours) and conventional culture requirements, restricting organism detection and only allowing retrospective analysis (days). This limits their usefulness in analysing air quality and risks of airborne transmission of infection. They provide limited data for standard setting and assessing the effect of interventions designed to increase air quality and decrease airborne infection risks. Direct continuous bioaerosol sampling is an established technology used to characterise ambient external air. Portable instruments such as the Wideband Integrated Bioaerosol Sensor (WIBS) combine laser particle size and shape detection with signals of particle viability (fluorescence from amino acids and NAD(P)H) characteristic of bioaerosols. This aim of this thesis was to investigate the utility of continuous monitoring approaches including WIBS and other instruments to characterise indoor air bioaerosols in hospital environments and evaluate the results of interventions designed to increase air quality. The WIBS-4A was used to characterise airborne biological particles in a 4-bedded hospital respiratory ward bay over a 4-week period before and during a plasma air treatment intervention designed to increase air quality. Twice-daily conventional impaction and settle plates and surface swabs were carried out in parallel with continuous WIBS bioaerosol monitoring. No statistical difference between conventional culture counts was detected during the plasma air treatment period compared with the control. Cumulative continuous monitoring plotted diurnally revealed raw numbers of airborne fluorescent particles were lowest at night, with four striking recurrent fluorescent particle peaks during the daytime when the number of particles increased by over 200-fold compared to the nocturnal minimum. These peaks corresponded to observed nebuliser use on the ward. WIBS analysis of the two nebulised therapy drugs used on the ward defined a characteristic fluorescence signature for nebuliser aerosols. This allowed design of a threshold filter to remove interferent nebulised drugs from fluorescent particle counts which did not eliminate bacteria when applied to experimentally aerosolised bacteria. Both raw and filtered WIBS data (excluding nebulised drug particles) showed a statistically significant ~28% reduction in fluorescent particles, (P<0.05), during the operation of the plasma disinfection unit. The clinical significance of this requires further study. The effect of footfall counts on bioaerosol concentrations was also monitored by deploying an infra-red footfall counter in tandem with the WIBS instrument. Both devices were successful in identifying that the highest footfall count coincided with the highest bioaerosol concentrations observed on the ward, which also coincided with the main morning staff shift change and handover. The cumulative filtered count data was used to devise a statistical threshold which could be the basis of a standard for the environment tested. The WIBS-4A was used in conjunction with the nebulised drug signatures to show that a portable extractor tent (Demistifier 2000, Peace Medical) was 100% efficacious in preventing spread of nebulised bronchodilator drug aerosols. This confirmed that use of Extractor tents prevents spread of drug particles from nebulised therapy. Air DNA samples were taken on six separate days over three months on the respiratory ward, and a preliminary analysis suggested that in most cases the largest single group at Phylum level were Firmicutes (Clostridiaceae/Clostridiales Families). Because these bacteria are potentially of gastrointestinal origin, it was hypothesized the source could be a communal lavatory that was present within the ward bay. A week-long WIBS campaign was therefore undertaken in a communal office toilet to investigate aerosol production from different toilet activities. Increased fluorescent particles were found in lavatory air on flushing after defaecation compared to other activities. Previous studies reporting the effect of toilet lids have found that they prevent the spread of visible droplets on flushing, however the effect on smaller particles was less clear cut. This study found that placing the lid down before flushing the toilet reduced the number of airborne fluorescent particles produced by flushing following defaecation, however it significantly increased particle size, shape, particle fluorescent intensity and residency time of defaecation-related particles in the air. A hypothesis is presented to account for this, involving acoustic reverberation magnification of flush-related turbulence by the lid, and implications of this for toilet design are discussed. This thesis highlights the ability of continuous bioaerosol detection by instruments such as WIBS to provide biologically meaningful characterisation of the healthcare environment. This characterisation facilitates airborne particle source attribution, allows provisional standard setting, and provides a powerful mode of assessment of the results of interventions designed to increase air quality.