UC Riverside

Aerosol particles are ubiquitous in the Earth’s atmosphere and play an important role in climate, air quality and health. The chemical composition of aerosol particles is complex and primarily associated with their source of origin. Once in the atmosphere, the composition is continuously evolving as a result of photochemical and heterogeneous chemical reactions. Consequently, composition-dependent properties that define the physical state and optical properties are also continuously changing, with important consequences for the dynamics and impacts of aerosols in the atmosphere. Laboratory-based methods have allowed an extensive exploration of the microphysical properties and chemical transformations of atmospheric aerosols. Single particle levitation methods are used to measure the microphysical properties of particles and connect with their evolving chemical composition. Properties such as size, hygroscopicity, phase morphology, and composition can be precisely measured by coupling levitation methods with analytical tools, such as mass spectrometry.

This dissertation describes the development of a new experimental platform connecting a linear quadrupole electrodynamic balance (LQ-EDB) with mass spectrometry (MS) that is capable of interrogating single levitated particles undergoing atmospherically relevant transformations. Two sampling methods, paper spray (PS) and an open port sampling interface (OPSI), were developed to transfer and ionize chemical analytes from levitated particles to the MS for compositional analysis. Laboratory studies were carried out to understand both non-reactive transformations and heterogeneous oxidation of levitated particles by precisely measuring their physical and optical properties as a function of evolving chemical composition. Non-reactive transformations include the particle-to-gas partitioning of semi-volatile species, while heterogeneous oxidation includes ozonolysis measurements on oleic and elaidic acid particles to understand the influence of particle phases on transformation kinetics and product distribution.

A key objective of this dissertation is to gain molecular-level understanding of how aerosol particles evolve due to chemical transformations and provide size-resolved detailed knowledge of their characteristics. It is essential to link the microphysical properties, composition, and reaction timescales for particles to quantify these evolving properties. Ultimately, the developments and measurements reported in this dissertation provide a foundation for exploring the chemistry of aerosol particles of complex composition and morphology to better understand their role in the environment.