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Title: Characterisation of carbonaceous particulate matter in Edinburgh
Author: Hammonds, Mark David
ISNI:       0000 0004 2733 0659
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2012
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Airborne particulate matter (PM) has important harmful effects on human health, as well as a number of other important atmospheric effects. Although progress has been made in understanding the sources and effects of PM, there remains considerable uncertainty on a number of issues, including the nature of a lot of the carbonaceous material, which comprises 30{50% on average of PM mass. This project aims to compare different methods of PM measurement, and contribute understanding to the nature and origin of the carbonaceous fraction of PM. Daily samples of PM10 were collected from three sites in the Edinburgh area using Partisol-Plus 2025 Sequential Air Samplers: 1) Urban Background (20 August 2008 until 21 April 2010); 2) Rural (25 February 2009 until 21 April 2009); and 3) Roadside (10 September 2009 until 21 April 2010). These localities provided PM that was, respectively, representative of: 1) city-wide background air; 2) air at a location distanced from population centres, roads and industrial areas; and 3) air influenced by the emissions associated with traffic. Gravimetric PM10 concentration (µgm-3) was determined for each daily filter sample, after a blank correction to compensate for the relative humidity (RH)-influenced change in filter mass over time. The correction was successful, with good agreement attained between the Partisol and a PM10 Tapered Element Oscillating Microbalance Filter Dynamics Measurement System (TEOM-FDMS) co-located at the Urban Background site. The general levels of PM10 measured in this monitoring campaign indicate that the air in Edinburgh was relatively clean. The main factor causing exceedance of the daily European Union (EU) limit value was shown to be transport of PM10 from areas of mainland Europe. High PM10 concentrations were also strongly associated with calm weather conditions in Edinburgh, which allowed the build-up of particulate pollution over time. Aethalometer-equivalent daily concentrations of black carbon (BC) were determined by measuring the optical reflectance of the PM10 filters from the Partisol samplers. The conversion of reflectance values to BC concentrations relied on a number of correction factors, which may have impacted on the accuracy of the results with time and location. The concentration of BC in Edinburgh was shown to be relatively low, with the daily variation being controlled by local emissions and meteorology. BC as a proportion of PM10 increased with sampling location in the order: Rural < Urban Background < Roadside. Predominantly traffic-related BC concentrations increased during periods of low wind speed and were not greatly influenced by long-range transport of aerosol. Daily water-soluble organic matter (WSOM) concentrations were obtained by aqueous extraction of the filter samples and measurement of the dissolved organic carbon (DOC). About 11% on average of the Edinburgh PM10 was WSOM. The majority of this WSOM seemed to have originated from air masses outside of the city, although there was a minor contribution from urban traffic sources. A solid phase extraction (SPE) procedure was used to isolate about one-third of the WSOM as hydrophobic compounds and this revealed a relative increase in the amount of less oxygenated material from traffic sources. Higher than average WSOM concentrations were strongly associated with calm weather conditions that allowed the transient build-up of particle concentrations. Some of the peaks in WSOM concentration were related to the transport of air masses from areas of mainland Europe where biogenic secondary organic aerosol (SOA) and biomass burning were likely sources. Analysis of the WSOM samples by UV-Vis absorption spectroscopy showed clear seasonal trends in the composition of hydrophobic watersoluble organic matter (HWSOM), interpreted as predominance of lower molecular weight aliphatic compounds in summer but predominance of larger aromatic and polyconjugated compounds in winter. Raman spectra were obtained for different carbonaceous reference materials. The results of curve fitting for these spectra gave D1 band full width at half maximum (FWHM) values that distinguished between diesel exhaust particles from a local bus and a humic acid sample. Analysis of Edinburgh PM10 samples using Raman microspectroscopy (RM) showed a variation in the structural order of the carbon compounds present between that of soot and HUmic-LIke Substances (HULIS), with a tendency towards more soot-like material being present. There was no strong relationship between carbonaceous order and BC concentration, showing that coloured organic compounds have the potential to influence reflectance measurements. The combination of these measurement approaches has yielded insights into the nature and variation in carbonaceous PM material with time and sampling location.
Supervisor: Heal, Mathew. ; Alexander, Andrew. Sponsor: Natural Environment Research Council (NERC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: particulate matter ; air pollution