Understanding the formation and evolution of biomass burning organic aerosol using non-target data approaches and mechanism development

Ambient biomass burning (BB) is the second largest source of organic aerosol (OA) and non-methane organic compounds to the atmosphere which can impact air quality and climate on local, regional and global scales. BB also includes domestic solid fuel combustion, which is a major contributor to particulate matter air pollution in many European cities. Global BB emissions are predicted to rise due to climate change, and growth in the domestic sector is also expected in the coming years. However, a detailed understanding of the chemical composition of emissions from BB and their reactivity in the atmosphere is lacking. This missing understanding is compounded by challenges in the quantification of chemical constituents contributing to OA. A central theme in this thesis is non-target analysis (NTA) of OA chemical composition. First, to overcome challenges facing quantification in NTA, namely the lack of analytical standards and non-universal ionisation in electrospray sources, a semi-quantitative methodology was developed for Ultra-High-Performance Liquid Chromatography coupled to Electrospray Ionisation High Resolution Mass Spectrometry (UHPLC-ESI-HRMS). It was observed that using the UHPLC-ESI-HRMS instrument response (i.e. peak area) could over- or under- estimate a species' abundance within a sample compared to semi-quantification, highlighting the need for quantification of species where no standards are available. Second, a semi-quantitative NTA of OA from wood burning determined compositional changes under different burning conditions and after aging. These results showed the relative aromaticity of the OA decreased upon aging but was dependent on the burning conditions which could have important implications for toxicity. Finally, chamber experiments evaluated the atmospheric photo-oxidation and secondary organic aerosol (SOA) formation of a methoxyphenol compound (guaiacol) emitted during BB. These experiments highlighted the different evolution of guaiacol SOA products in between night and daytime and provides direction for future research.