Pignatelli, Alessia (2026) MULTISCALE OXIDATIVE CHEMISTRY OF CARBONACEOUS EMISSIONS: INVESTIGATION OF RADICAL PATHWAYS AFFECTING SOOT AND SECONDARY ORGANIC AEROSOL FORMATION. [Tesi di dottorato]

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Abstract

Atmospheric aerosols impact both climate and human health, but despite their key role, the chemical pathways driving their formation and atmospheric evolution remain only partially understood. Atmospheric aerosols can be released by biogenic sources, such as vegetation and volcanic eruptions, or by anthropogenic activities, including combustion and industrial processes. Carbonaceous emissions from combustion represent a major anthropogenic source of both primary particles, such as soot, and gaseous precursors involved in secondary organic aerosol formation (SOA). This thesis investigates the oxidative chemistry of carbonaceous emissions from various sources, with particular focus on anthropogenic combustion emissions. A multiple-angled approach was adopted here, aiming at clarifying the role of radical pathways in soot formation, isolating the impact of atmospheric aging on primary organic aerosol (POA) and SOA formation and evolution, and monitoring the interactions of anthropogenic emissions with other pre-emitted compounds. The work is organized in three work packages, addressing combustion-scale processes, laboratory based atmospheric aging, and atmospherically relevant conditions. The key findings of this thesis highlighted the possibility of using dopants to inject into different combustion systems to alter the formation of soot and, more generally, the release of harmful compounds. The introduction of ozone in a methane-air system proved to alter the chemistry of the system by impacting on the formation mechanism of π-radicals, critical intermediates in soot formation. Furthermore, the monitoring of atmospheric aging of emissions released by ethylene-air flames are here presented. Atmospheric aging was performed using an oxidation flow reactor that mimics OH-induced oxidation. Mass spectrometric analysis and particle-size distribution measurements highlighted several differences in the composition and structure of primary and secondary organic aerosols. Finally, atmospheric evolution of anthropogenic emissions, coupled with their interactions with biogenic compounds, was investigated. The experiments were conducted at CLOUD, CERN facility under controlled conditions mimicking forested, suburban, and highly polluted environments. These experiments focused on deciphering the role of RO2 in atmospheric reactive pathways and, remarkably, on understanding the impact of different precursors on RO2 structure and RO2-RO2 interactions.

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