UC Riverside

Aerosol particles in the atmosphere negatively impact air quality and have a strong influence on the Earth’s climate due to their direct and indirect radiative effects. Characterization of the chemical and optical properties of these aerosol particles are critical to mitigate global climate change and improve air quality. My dissertation focuses on exploring the chemical and optical properties of laboratory generated secondary aerosols, which constitute a large fraction of aerosols in the atmosphere.In the first study, secondary organic aerosols (SOA) were produced through photooxidation of volatile organic compounds (VOCs, 1-methylnaphthalene or longifolene) under variable ammonia (NH3), nitrogen oxides (NOx), and relative humidity (RH) conditions. I studied SOA chemical and optical properties of the resulting SOA. This study shows that the formation of chromophores in SOA is strongly affected by different environmental conditions. NOx, NH3 and elevated RH enhance the absorption of aromatic SOA. In the second study, I investigated the SOA formed from pure and mixtures of anthropogenic (phenol and 1-methylnaphthalene) and/or biogenic (longifolene) VOCs using continuous-flow, high-NOx photooxidation chamber experiments. SOA optical properties and chemical composition were explored. Additionally, the absorption of multi-VOC SOA was predicted based on the linear-combination assumption and compared with the measured absorption. This study highlights the presence of multiple VOCs could have non-linear effects on the chemical and optical properties of the mixture SOA. In the third study, I used a machine learning model to study the SOA mass spectra data to predict its mass absorption coefficient (MAC). The prediction results indicate the strong correlation between SOA mass spectra and absorption, and machine learning model could be us absorption potential, in the form of MAC, despite lack of molecular level information on chromophores. In the fourth study, secondary aerosols formed through oxidation of dimethyl sulfide (DMS), a dominant natural volatile organic compound released from the ocean, were explored. I studied the DMS aerosol chemical composition with a mass spectrometer. This study reveals the formation of important sulfur products from DMS under different atmospheric aging time and the presence of highly-oxygenated long-lived organic products from DMS oxidation, which has been less studied before.