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Title: Characterisation of urban particulates and their potential health effects
Author: Charlton, Alexander James
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2011
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Urban particulate matter (UPM) is known to be a causative agent in a number of diseases including cancers of the respiratory system. Toxicological analysis has implicated particle size, surface area, metal ions, free radical induction, and organic chemistry as potential drivers of human health effects; however the relative importance of these factors is unclear. This project attempts to determine the factors responsible for the in vitro toxicity of particulate air pollution. The importance of fuel type on exhaust particle characteristics was examined through the collection of engine exhaust particles (EEP) produced by a heavy diesel engine operating using conventional diesel and rapeseed oil based biofuels. The effects of particle aging in the atmosphere, and the contributions of sources other than engine exhausts were determined through the collection of UPM from a roadside site. The genotoxic potential of particulate samples was determined using the comet assay, and particle free radical induction was measured with the plasmid strand break assay. Particle organic chemistry was determined using gas chromatography mass spectrometry. Particular emphasis was placed on the accurate quantification of polycyclic aromatic hydrocarbons (PAH), a class of carcinogenic hydrocarbons known to be present on the surface of particulate matter. Engine particulate samples were collected from a heavy duty diesel engine using conventional petrodiesel, rapeseed oil (RSa) or rapeseed oil with a fuel additive (RSaAd). Analysis of particulate specific emissions indicated that Rsa combustion generated a significantly greater mass of particulate matter than the combustion of diesel. This increase in particulate mass output was attributed to poor RSa combustion characteristics due to coking of fuel injectors during engine operation. ' This could be corrected through the use of a fuel additive, which bought Rsa particulate emissions into line with diesel. In all fuels the majority of the particulate mass collected had an aerodynamic diameter of less than one 1 urn, indicating that they may potentially deposit within the lower respiratory tract in humans, and as such are relevant to human health. Analysis of total suspended particle and size fractionated samples of engine particulate material showed that engine exhaust particles produced through diesel combustion were significantly more genotoxic than those produced whilst operating with biofuels. A statistically significant size dependency was found in diesel exhaust particles, with finer material inducing a greater level of DNA damage. Finer rapeseed oil exhaust particles were also shown to be more genotoxic than coarser material, although this trend was not as pronounced as in diesel exhaust particles, and was not statistically significant. Free radical analysis of exhaust particles showed that for all fuels the coarsest fraction of PM induced the largest level of radical activity. In most fractions diesel and Rsa EEP induced similar levels of damage, whereas coarse RSaAd induced significantly greater levels of free radicals. Free radical induction was indicated to be a result of particle phase metals present due to engine wear. Diesel EEP P AH levels were higher than Rsa or RSaAd samples in most size fractions of particles examined. Diesel EEP showed finer fractions to have the greatest P AH concentrations, with P AH concentration being roughly in line with v what might be expected based on projected surface area, suggesting absorption from the vapour phase as the mechanism by which P AH arrive on diesel PM. RSO and RSOAd EEP contained significantly lower P AH concentrations than diesel EEP. A correlation was found between particle phase P AH concentrations and observed DNA damage in the comet assay, suggesting PAH as potential drivers of genotoxicity. The concentration and distribution of n-alkane species was shown to be independent of fuel type, which is in line with previous studies that have indicated that engine lubricating oil is the major source of particle n-alkanes. Qualitative analysis of compounds other than P AH and n-alkanes in EEP showed differences in composition between diesel and RSO derived EEP, with the latter containing a greater number of oxygenated compounds. Size fractionated samples of UPM were collected from the Kirkstall Road air monitoring enclosure, located on a busy road servicing Leeds city centre. As in engine experiments the majority of particulate mass was found to be present in finer particles. In addition to particle size seasonal effects were observed with higher particle mass concentrations observed during colder sampling periods. Comet assay analysis of size fractionated UPM indicated that the majority of DNA damage was observed in the finest fraction of particles. However this damage was lower than that observed in the finest fraction of diesel EEP. In general particles collected during colder periods exhibited greater levels of DNA damage than those collected during warm sampling periods. As in diesel EEP the majority of the particle phase P AH detected were in the finest fractions of particulate material. Coarse UPM fractions contained a greater proportion of total particle phase P AH contributions than was observed in diesel EEP, possibly indicating particle agglomeration in the atmosphere. Additionally, a seasonal component was observed, with particles collected during colder seasons generally containing greater levels of PAH. A strong correlation between particle PAH concentrations and DNA damage in the comet assay was observed, indicating that the mechanism by which DNA damage occurs may involve PAH. Free radical analysis showed that the trend observed in EEP was reversed in UPM, with the finest fractions of UPM inducing greater levels of plasmid unwinding. This was at odds with the results of analysis of free radicals by EEP. The reason for this difference was unclear; however this may be a result of UPM and EEP inducing free radical activity by different mechanisms. The use of PAH diagnostic ratios and analysis of n-alkane species distribution indicated that the anthropogenic sources of particulate matter predominate at the roadside. There was evidence that UPM represented a more complex chemical mixture than EEP, with a greater number of particle bound organic compounds. The majority of these species were oxygenates, indicating oxidative processing of particles during atmospheric residence.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available