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|Title:||Single Particle Mass Spectrometry: Data Analysis Techniques and Applications in Atmospheric Aerosol Research|
|Publisher:||School of East, Atmospheric and Environmental Science|
|Abstract:||Airborne particles have adverse effects on human health and climate. Many of those effects are yet poorly understood, and more efforts are needed to characterize the atmospheric behaviour and properties of aerosols. This thesis presents the development and use of a mass spectrometric method for analysing single aerosol particles. This novel information can help unravel the uncertainties in aerosol impacts. The Single Particle Analysis and Sizing System, SPASS, is an instrument able to provide physico-chemical information about single particles in the size range ~300 nm ¿ 3 µm. Traditional techniques are not able to provide information on a single particle basis. The SPASS uses a Nd-YAG laser to vaporize and ionize single particles (Laser Desorption Ionization, LDI). The ions produced are analyzed by Time-Of-Flight mass spectrometry. Detailed description of the technology, and a review of recent applications of LDI instruments have been performed. This PhD focuses on the applicability of the SPASS to different situations, tries to understand what information single particle mass spectrometry can provide and where it adds to the knowledge already at disposal. The capability of the SPASS to analyze natural and anthropogenic particles, both primary and secondary, has been tested. The instrument can detect hygroscopic salts, soot, diesel exhaust, secondary organic aerosol, amines and iodine, and a large number of elements of the periodic table. Softer fragmentation of compounds has been obtained with low laser power intensities. The SPASS has taken part on several field campaigns, obtaining information about mixing state, sources and further processing of single particles in the atmosphere. Residential coal combustion was identified as the main cause of a severe smog episode that took place in winter time in Krakow, Poland. Traffic was not a significant source. On a lighter smog episode, industrial coal combustion was relatively more important, with an increase of traffic contribution. Secondary aerosols with nitrate were predominant during clean conditions. A source of single particles containing amines was identified in indoor environments, not present outdoors. Analysis of single particles at Mace Head, Ireland, showed fresh NaCl in air masses from a clean oceanic origin, and characterized the aging of the particles through the degree of displacement of Cl by N when the air masses came from polluted regions in continental Europe. Internal mixtures of sea salt and carbon, and sea salt and magnesium were found in single particles, and a tentative approach to relate them to marine biological activity has been explored. Using especial Föhn winds, differences in the primary produced single particles in an urban location (Milan) and in a rural area (Ispra, Po Basin) have been found and characterized. During stagnant conditions, secondary species were predominant, and were totally apportioned to the regional background aerosol. A review of available data analysis techniques has been performed. K-means clustering algorithm and ART-2a Artificial Neural Network algorithm have been described in detail, and have been applied to the data SPASS data. 2007 PhD Thesis Daniel Mira Salama|
|JRC Institute:||Institute for Environment and Sustainability|
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