Vacuum Ultraviolet (VUV) photoionization mass spectrometry has been used to measure the evolution of chemical composition for two distinct organic aerosol types as they are passed through a thermodenuder at different temperatures. The two organic aerosol types considered are primary lubricating oil (LO) aerosol and secondary aerosol from the alpha-pinene + O3 reaction (alphaP). The evolution of the VUV mass spectra for the two aerosol types with temperature are observed to differ dramatically. For LO particles, the spectra exhibit distinct changes with temperature in which the lower m/z peaks, corresponding to compounds with higher vapor pressures, disappear more rapidly than the high m/z peaks. In contrast, the alphaP aerosol spectrum is essentially unchanged by temperature even though the particles experience significant mass loss due to evaporation. The variations in the LO spectra are found to be quantitatively in agreement with expectations from absorptive partitioning theory whereas the alphaP spectra suggest that the evaporation of alphaP derived aerosol appears to not be governed by partitioning theory. We postulate that this difference arises from the alphaP particles existing as in a glassy state instead of having the expected liquid-like behavior. To reconcile these observations with decades of aerosol growth measurements, which indicate that OA formation is described by equilibrium partitioning, we present a conceptual model wherein the secondary OA is formed and then rapidly converted from an absorbing form to a non-absorbing form. The results suggest that although OA growth may be describable by equilibrium partitioning theory, the properties of organic aerosol once formed may differ significantly from the properties determined in the equilibrium framework.

This dissertation presents findings from three independent but complementary studies addressing aerosol filtration efficiency of and in-room air cleaner and laboratory and field studies on the optical properties of absorbing aerosols in the atmosphere. First, the performance of a low-cost, DIY air cleaner that uses MERV-13 filters coupled with a standard box fan, known as the Corsi-Rosenthal Box (CR Box), was assessed using both research-grade instrumentation and low-cost sensors. The effective clean air delivery rate (CADR) depends on fan speed and ranged from 600 to 850 ft³ min⁻¹ (1019 to 1444 m³ h⁻¹), demonstrating the CR Box’s effectiveness in reducing indoor particle concentrations as a cost-efficient alternative to more expensive, commercially available HEPA air purifiers. Second, we described and characterized the performance of a humidified cavity attenuated phase shift spectrometer (H-CAPS-PMSSA) system that measures aerosol extinction and scattering, from which aerosol absorption is derived, and which has been modified to enable measurements at varying relative humidities up to ~90%. Using an updated truncation correction method, the modified system allows for accurate measurement of the effects of water uptake on light absorption, revealing critical insights into humidity-driven absorption enhancement. Lastly, during the Tracking Aerosol Convection Interactions Experiment (TRACER) campaign in Houston, Texas, optical properties of black carbon (BC), brown carbon (BrC), and dust were characterized. Measured mass absorption coefficients (MAC) were determined for BC, BrC, and dust were retrieved along with the dust refractive index. Significant contributions of dust and BC to regional absorption were determined, with BC accounting for 61% and 75% of absorption at 405 nm and 532 nm, respectively, dust accounting for 34% and 16% of absorption at 405nm and 532nm, and BrC accounting for 6% and 9%, respectively. These studies collectively advance understanding of cost-effective indoor air cleaner performance, aerosol optical properties under humidified conditions, and the optical properties of absorbing aerosols in complex urban environments.