Sasso, Fabio (2025) SECONDARY AEROSOL FORMATION FROM COMBUSTION SOURCES: THE ROLE OF PRIMARY PRECURSORS OF ORGANIC AND INORGANIC PARTICULATE MATTER. [Tesi di dottorato]

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Abstract

Atmospheric aerosols play a pivotal role in influencing climate, air quality, and human health. Aerosols can interact with solar radiation, directly by scattering and absorbing light, and indirectly by modifying cloud properties and lifetimes. These interactions significantly impact the Earth's radiative balance, contributing to climate forcing, while also posing risks to respiratory and cardiovascular health when inhaled. Among atmospheric aerosols, secondary aerosols, which include secondary organic aerosol and secondary inorganic aerosol are particularly significant due to their abundance and complex formation mechanisms. Secondary organic aerosol, formed through the oxidation of volatile organic compounds and secondary inorganic aerosol, derived from the transformation of precursor gases like nitrogen oxides, sulphur dioxide and ammonia, represent key fractions of fine particulate matter. The formation pathways of these aerosols are influenced by a multitude of factors, including precursor concentrations, environmental conditions (temperature, humidity, and sunlight), and the presence of co-reactants. Despite extensive research, many uncertainties remain regarding the specific roles of various precursors, the interaction of chemical and physical processes, and the influence of anthropogenic activities. Understanding the mechanisms behind secondary aerosol formation is critical for several reasons. First, it allows for improved modelling of atmospheric processes and better predictions of air quality and climate impacts. Second, it provides essential insights into the sources of particulate matter, enabling the development of targeted emission reduction strategies. This study explores the potential precursors of atmospheric secondary aerosols emitted directly into the atmosphere from the exhaust of different combustion sources. The research begins with the study of gaseous and carbonaceous products extracted from a controlled ethylene-air combustion system using a premixed burner. This approach provides a detailed understanding of the primary emissions and their transformation pathways in laboratory scale. Subsequently, a dynamic system was employed with modern light duty passenger vehicles to simulate and analyse secondary aerosol formation from vehicle’s gaseous and particulate exhausts. By examining a range of fuels, including traditional gasoline and diesel, as well as renewable alternatives, we assess the impact of fuel properties on hydrocarbon, nitrogen oxides, and ammonia emissions, and their subsequent contribution to secondary organic aerosol and secondary inorganic aerosol formation. Our findings demonstrate that reducing aromatic compounds in gasoline and introducing oxygenated additives such as methanol and ethanol can lower hydrocarbon and secondary organic aerosol emissions. Diesel fuels without aromatic chains exhibit superior performance in minimizing secondary aerosol production. These results underscore the importance of investigating fuel reformulation as a strategy to mitigate secondary aerosol emissions. By elucidating the key factors and mechanisms involved, this work contributes to improved air quality models and provides a scientific basis for policy decisions aimed at reducing the environmental and health impacts of particulate pollution.

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