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Title: The characterisation of urban airborne particles and the influences behind their concentrations and composition
Author: Young, David Thomas
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2007
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Sampling of airborne particle number concentrations was carried out in roadside locations in Leicester and Manchester, UK. A DMS500 was used to measure particle size distributions betWeen 4.87 and lOOOnm in both locations and a lognoimal fitting procedure was used :to model the modal parameters present within the size distributions across the diurnal cycle. For the most part, five modes were found to best describe the diurnal hourly averaged number size distributions in both locations. Two modes were found to exist below approximately 20nm, and were termed nucleation modes. These were believed to arise from primary and secondary sources, predominantly consisting of externally mixed liquid aerosol particles. These were thought to have arisen from binary and ternary nucleation ofprecursor gases such as, NOx, SOx and NH3, or through photochemically induced nucleation of organic species, especially aromatics arising from vehicle exhaust. Also the condensation of unburnt fuel may contribute to these modes~ Two further modes were found to exist between approximately 20nm and 150nm and were termed Aitken modes. These were believed to consist predominantly of \. internally mixed particles, have a solid core with a coating of organic and inorganic compounds arising as a direct vehicle exhaust emission. A much smaller mode which generally contributed less than 5% to total number concentrations, termed the accumulation mode, was found to exist >150nm and was likely to have arisen due to agglomeration of smaller Aitken mode particles. Both nucleation and Aitken mode number concentrations shared strong correlations with traffic flow during free-flow conditions. The relationship was seen to break down during busier traffic conditions, when often lower particle concentrations occ~rred, likely due to reduced vehicle speeds during such times. The Aitken mode particle count shared a strong decay relationship with wind speed in both locations, whilSt no relationship was seen between the nucleation mode count and wind speed in Manchester and only a weak decay relationship was seen in Leicester. This is likely due to the competition between existing Aitken mode particle counts and nucleation (new) particle formation. The absence of a relationship between nucleation' mode and wind speed in Manchester is thought to have been the case since new particle formation from gaseous precursors balanced dilution and dispersion occurring as aresult of increased wind speed. The weak decay relationship seen in the Leicester roadside location may have resulted due to scavenging ofgaseous precursors responsible fOf new particle formation at this locatio~ due to higher preexisting concentrations. Short time scale measurements of particle counts in Leicester showed the transient nature of particle concentrations in the roadside environment, with particle counts on a second by seCond basis often an order ofmagnitude higher than the 3 minute mean concentration. At times during each hour, these excursions, especially for the Aitken mode, were found to contribute up to one fifth to total hourly particle counts and yet only lasted for a few minutes in total during each hour. The Aitken mode particles dominating these excursions are thought to be more biologically persistent than the nucleation mode particles, ~eing able to pe~etrate deep into the lung carrying a range oftoxic inorganic and organic compounds. A high volume sampler was used to collect size segregate particulate matter at a roadside location in Leeds, UK. Four size fractions below l0J.lm, including ultrafines were analysed for a range oftrace elements present using a sequential extraction scheme. Elements predominantly distributed within the fmer particles (<2.5J.lffi) included Pb, V, Rh, Ti, K, Ni, Si, rn: Pt, Se, Cr, Co, Pd, Ce, Ag and La, whilst elements predominantly distributed within the coarser size fractions (> IJ.lm) included Mg, Mn, AI, Cu, ~a, Ba, Fe, and Ca Most elements within the ultrafine size fraction were found to be larg~ly insoluble. Ni was found to be present Within PMIO at concentrations which may result in an increased excess lifetime risk of carcinogenic effects. Fe was one of the most insoluble elements found in the ultrafine size fraction, which was indicative of the type of Fe present in this size fraction, Fe3+, which is responsible for ... driving redox reactions in the lung ~hich can ultimately result in inflammation through oxidative stress. A significant amount of Pb was present within the size fraction between 0.1 and IJ.lm, likely arising due to a comb.ination of lead deposited in roadside soils from previous leaded gasoline use and long range transport from industrial sources. Additionally, a further potential source of Pb is from weights used to balance vehicle wheels which are deposited and ground up by passing vehicles.
Supervisor: Not available Sponsor: Not available
Qualification Name: The University of Leeds, 2007 Qualification Level: Doctoral
EThOS ID:  DOI: Not available