Wang, Sheng-Wei; (2024) Concentration of PAHs on different soot particle sizes generated by pyrolysis of a wide range of fuel molecules. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Particulates and polycyclic aromatic hydrocarbons (PAH) are products of incomplete combustion from various human activities. The PAHs are carcinogenic to humans and are attached to particulates of different sizes. It is these volatile organic compounds (VOC) that are responsible for the adverse health impacts on humans. The fine particulates are capable of penetrating deep into the lungs while possessing great deposition efficiency, especially those in the ultrafine region (<100nm). The greater the attachment of these toxic PAHs to ultrafine particles, the more dangerous the health impact becomes, as they can be delivered deeper into the lungs, causing more severe health issues. This indicates that the health effects of particulate PAHs are strongly size-dependent. As there is a transition away from fossil fuels to future renewable fuels, there is a need to understand potential correlations between fuel molecular effects on the particulate PAH size distribution. This thesis therefore investigates the effect of fuel molecular structure on the particulate size distribution and the associated PAH distribution across particles of different sizes, specifically, looking at a series of C6 hydrocarbons each containing a different functional group. T t st u ls w r suppl to n oxy n r l m n low r tor t n t onst nt r on low rate of 10000ppm on a C1 basis. Soot particles from the pyrolysis of all the fuels were sampled and segregated using a nano-MOUDI cascade impactor, capable of separating particles into 15 size segments from 10 nm to 18 µm. Condensed PAH were subsequently extracted from the size segregated particles and quantified by gas chromatography mass spectrometry (GC-MS). 16 priority PAHs listed by the US EPA were investigated, paying specific attention to the 7 PAHs highlighted by the EPA as the B2 group, which are categorised as possibly carcinogenic to human. The results indicated that oxygenated fuels tend to promote the formation of smaller particles. Consequently, a higher degree of PAH condensation on the finer particles was observed during oxygenated fuel pyrolysis compared to other fuel structures. Aromatic structures were observed to exhibit the highest degree of soot formation; however, this resulted in a limited abundance of PAH formation. As a result, a lower amount of total PAHs was found attached to the aromatic fuel-induced particles. Nevertheless, the attached PAH species from the aromatic and cyclic fuel structures were more carcinogenic, with a higher degree of toxic PAHs attached to various particle sizes. Regarding the influence of fuel on PAH particle size distribution, ester structures exhibited the lowest median mass aerodynamic diameter (MMAD), indicating that PAHs tend to be attached to smaller particles compared to other structures, while alkane structures exhibited the opposite trend, with PAH distribution tending to be on larger particles with the highest MMAD.

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