UC Riverside

The Earth’s atmosphere is composed of an enormous variety of chemical species associated with trace gases and aerosol particles whose composition and chemistry have critical impacts on the Earth’s climate, air quality, and human health. Reactive volatile organic compounds (VOCs) and organic aerosols (OAs) in the atmosphere can be oxidized by oxidants in the atmosphere through a number of pathways, generating critical intermediate products such as the peroxy radicals (RO2•), as well as the subsequent closed-shell oxygenated species which are a highly variable class of organic mixtures with diverse functional groups, such as ketone, alcohol, carboxylic acid, hydroperoxide, etc. Due to the significance to atmospheric environment, it is imperative to elucidate RO2•-centered chemistry and understand chemical compositions of the resultant OAs on the molecular and even isomeric level. Mass spectrometry analysis as a powerful and popular analytical technique has been widely developed and applied in atmospheric chemistry for decades. In combination with a comprehensive set of mass spectrometry instrumentation and kinetic simulations, this dissertation aims to help better understand OA formation and evolution and provide new insights in the realistic understanding of atmospheric components.Chapter 1 introduces and reviews recently developed mass spectrometry techniques that allow for effective detection, identification, and quantification of a broad range of organic and inorganic chemical species with high sensitivity and resolution. Chapter 2, 3, 4 focus on probing RO2•-centered bimolecular reactions in the gas phase and the particle phase that have been understudied in previous research. In Chapter 2, we demonstrate interferences caused by secondary ion chemistry in iodide-adduct chemical ionization mass spectrometry (I−-CIMS) which has been a popular analytical technique to measure a wide range of oxygenated VOC (OVOCs) due to its low selectivity. Moreover, we apply the secondary ion chemistry to inform OVOCs’ functionalities and hence formation mechanisms. Chapter 3 illustrates that condensed-phase bimolecular autoxidation largely accelerates OA aging under atmospheric oxidant concentrations and impacts aerosol compositions, reversing a conventional view that multiphase (i.e., heterogeneous) oxidative aging is a slow process. Chapter 4 expands the heterogeneous study to the organic hydroperoxide formation from RO2• + HO2• reactions at aerosol particle interface via hydrogen-deuterium exchange mass spectrometry. This dissertation provides novel advancements in mass spectrometry applications and a better understanding of the atmospheric chemical mechanisms. It may help interpret existing datasets, develop effective experimental approach to simulate atmospheric OA processes, and improve models to accurately predict OA transformation in the atmosphere.