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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
71

Measuring aerosol nanoparticles by ultraviolet photoionisation

Nishida, Robert Takeo January 2019 (has links)
Aerosol particulate matter adversely affects the climate, environment and human health. Mechanistic studies have indicated that ultrafine aerosol nanoparticles, those under 100 nm in diameter, may have significant health impacts due to their relatively high number concentration, surface area and potential for deep penetration into the human lung. However, epidemiological evidence remains limited due to the lack of measurement networks that monitor local concentrations of ultrafine particles. Direct ultraviolet (UV) photoionisation electrically charges aerosol nanoparticles for subsequent detection by a mechanism distinct from the ion-particle collisions of conventional methods. The aim of this work is to evaluate photoionisation theory in order to understand and interpret measurements from a low-cost aerosol particle sensor. To accomplish this, theoretical equations are analysed, modelled and compared with experimental results for validation. The photoelectric yield of aerosol particles is explored in terms of particle size, concentration, material, and morphology giving insight into the interaction of light and particles. This thesis introduces the first analysis of photoionisation, recombination, convection/diffusion and transport of particles in an electric field using analytical, numerical, and computational fluid dynamics (CFD) techniques. Characteristic times and dimensionless parameters are defined to determine regimes under which the measurement system is dominated by each of the charging or transport mechanisms. The level of modelling detail required for accurate prediction of aerosol charging and capture methods is demonstrated over a range of conditions. In a continuous flow of aerosol particles, an electric field is applied to capture charge as it is photoemitted from particles and before the emitted charge and particles can recombine. This method yields a novel current measurement directly representative of photoemission. The CFD model agrees well with electrical current measurements demonstrating that the physics of the problem is suitably represented. It is demonstrated that photoemission is linearly proportional to total (mobility) surface area for a large range of sizes and concentrations of particles of self-similar material and morphology, with agglomerated silver particles having 5$\times$ yield of agglomerated carbon from a propane flame. It is shown for the first time that agglomerated particles have a significantly higher photoelectric yield (2.6$\times$) than sintered, close-packed spheres of the same mobility diameter and material, directly contradicting two of the three previous relevant studies. Close-packed spheres have less material exposed to both the photon flux and the particle's surroundings than an agglomerate of the same particle mobility diameter, thereby reducing photoelectric activity. The photoelectrically active area is defined explicitly in this work to reflect the effect of a particle's morphology; the revised definition produces good agreement with experimental results.
72

Measurements of carbonaceous aerosol across the U.S. : sources and role in visibility degradation /

Shah, Jitendra J. January 1981 (has links)
Thesis (Ph. D.)--Oregon Graduate Center, 1981.
73

The role of meteorological dispersion and space heating demand in ambient concentrations of carbonaceous aerosols /

Rau, John A. January 1981 (has links)
Thesis (M.S.)--Oregon Graduate Center, 1981.
74

A factor model of urban aerosol pollution : a new method of source identification /

Henry, Ronald Claude. January 1977 (has links)
Thesis (Ph. D.)--Oregon Graduate Center, 1977.
75

Generation of soot particles and studies of factors controlling soot light absorption /

Lee, Keh-Tarng. January 1983 (has links)
Thesis (Ph. D.)--University of Washington, 1983. / Vita. Bibliography: leaves [115]-123.
76

On the lifecycle of aerosol particles : Sources and dispersion over Scandinavia

Tunved, Peter January 2004 (has links)
Aerosol particles are likely important contributors to our future climate. Further, during recent years, effects on human health arising from emissions of particulate material have gained increasing attention. In order to quantify the effect of aerosols on both climate and human health we need to better quantify the interplay between sources and sinks of aerosol particle number and mass on large spatial scales. So far long-term, regional observations of aerosol properties have been scarce, but argued necessary in order to bring the knowledge of regional and global distribution of aerosols further. In this context, regional studies of aerosol properties and aerosol dynamics are truly important areas of investigation. This thesis is devoted to investigations of aerosol number size distribution observations performed through the course of one year encompassing observational data from five stations covering an area from southern parts of Sweden up to northern parts of Finland. This thesis tries to give a description of aerosol size distribution dynamics from both a quantitative and qualitative point of view. The thesis focuses on properties and changes in aerosol size distribution as a function of location, season, source area, transport pathways and links to various meteorological conditions. The investigations performed in this thesis show that although the basic behaviour of the aerosol number size distribution in terms of seasonal and diurnal characteristics is similar at all stations in the measurement network, the aerosol over the Nordic countries is characterised by a typically sharp gradient in aerosol number and mass. This gradient is argued to derive from geographical locations of the stations in relation to the dominant sources and transport pathways. It is clear that the source area significantly determine the aerosol size distribution properties, but it is obvious that transport condition in terms of frequency of precipitation and cloudiness in some cases even more strongly control the evolution of the number size distribution. Aerosol dynamic processes under clear sky transport are however likewise argued to be highly important. Southerly transport of marine air and northerly transport of air from continental sources is studied in detail under clear sky conditions by performing a pseudo-Lagrangian box model evaluation of the two type cases. Results from both modelling and observations suggest that nucleation events contribute to integral number increase during southerly transport of comparably clean marine air, while number depletion dominates the evolution of the size distribution during northerly transport. This difference is largely explained by different concentration of pre-existing aerosol surface associated with the two type cases. Mass is found to be accumulated in many of the individual transport cases studied. This mass increase was argued to be controlled by emission of organic compounds from the boreal forest. This puts the boreal forest in a central position for estimates of aerosol forcing on a regional scale.
77

Methodological issues in ultra-low concentration aerosol sampling

McCutcheon, Heather Jean, January 2002 (has links) (PDF)
Thesis--University of Oklahoma. / Includes bibliographical references (leaves 45-46).
78

Characterization of Finnish arctic aerosols and receptor modeling

Basunia, M. Shamsuzzoha. January 2002 (has links) (PDF)
Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.
79

The dependence of aerosol scattering on relative humidity and particulate composition

Mooiweer, Wiesje. January 2008 (has links)
Thesis (M.S.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Mar. 9, 2010). Includes bibliographical references (p. 173-182).
80

Acidity and sampling artifacts of PM2.5 in Hong Kong /

Pathak, Ravi Kant. January 2004 (has links)
Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references (leaves 122-135). Also available in electronic version. Access restricted to campus users.

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