Physico-chemical characterization of combustion generated inorganic nanoparticles

Combustion generated particulate matter is widely recognized to be the major pollutant in urban areas because of stationary combustor and vehicular traffic sources. Particularly the ultrafine fraction was proven to have the highest impact on human health since its ability to deeply penetrate the lung and the circulatory system and to be enriched in toxic condensable species because of the large specific surface area. Up to recent times the nanometric fraction, i.e. below 10nm, was not taken in consideration, despite it is the most toxic, because it was assumed that such small particles meet and coagulate at gas kinetic rate so that their lifetime was negligible small. Some recent results on carbonaceous nanometric particles generated in laboratory flames showed that, at high temperatures, their coagulation as well their collection efficiencies drops dramatically orders of magnitude as their size decreases below 5nm. Consequently they could escape from combustors and filters and survive in the atmosphere in a not negligible amount. Ashes and additives present in practical fuels, biomass and wastes contain a not negligible amount of metals which brought at high temperature, cause the emission of ultrafine particles. The fraction with size smaller than 10nm of such inorganic particles was not yet studied neither measured at the exhaust of combustors despite it is well known that the addition of trace amount of metals to a flame causes the formation of nanoparticles. The aim of the research activity described in this thesis is to characterize such small toxic metal nanoparticles and to verify if they could be released at the exhaust of combustion systems because their coagulation and collection efficiency, at high temperature, follow the same trend of carbonaceous nanoparticles. The thesis is composed of three main part roughly corresponding to the three year of the research activity. The first two chapters contains the background information on combustion generated particles and aerosol dynamic. The chapters two and three describe the followed experimental methodologies while the third parts contain the results and the relative discussions. Reactors consisting of flat laminar premixed flames doped with real fuels or toxic metal particles precursors were developed and successively investigated. They allow to perform spatially resolved measurements, at several residence time in flame, of incipient inorganic nanoparticles generated in a well controlled environment. Diagnostics with high sensitivity to particles of few nanometers in size were chosen to this aim. They are on-line sampling probe high resolution Differential Mobility Analysis and in- situ Laser Light Scattering. Particles thermophoretic collection for extra-situ Atomic Force Analysis was widely used too.