Abstract: Atmosphere aerosols, including secondary organic aerosols (SOA), are ubiquitous constituents in the atmosphere. During their lifetimes, these aerosols can be transported hundreds of kilometers from their source and can undergo a variety of chemical and physical changes depending on the atmospheric conditions (e.g., acidity). However, SOA formation and aging processes--including the influence of acidity on these processes--are the leading source of uncertainty in aerosol radiative forcing in global climate models. The main objective of this thesis is to explore the influence of acidity on the chemical composition and optical properties of organic aerosols. This is achieved through laboratory studies that offer a detailed molecular-level understanding of the synergistic interactions between monoterpene oxidation products and anthropogenic compounds like sulfuric acid (H2SO4). By integrating these laboratory studies along with future field measurements and model predictions, informed decisions can be made to tackle the environmental issues associated with air quality and climate change