Aerosol particles are important in air quality, climate, and human health. They can affect the earth’s energy budget directly by scattering and absorbing solar radiation and serve as cloud condensation nuclei (CCN), thus influencing cloud properties and lifetime. Atmospheric aerosols are formed through a wide variety of natural and anthropogenic sources. This dissertation presents a comprehensive investigation into the behavior of water-soluble organic molecules on atmospheric aerosol surfaces using Second Harmonic Scattering (SHS). The study focuses on understanding the partitioning of these molecules at the aerosol surface, a crucial aspect in atmospheric chemistry impacting cloud formation, radiation balance, and air quality. The research is divided into three main parts. Initially, the study explores the disposition of organic molecules on aerosol surfaces, utilizing a modified Langmuir model to describe their behavior. This part emphasizes the predominant residence of these molecules on the aerosol surface, highlighting the surface's significant role in atmospheric reactions. The second part examines the interactions between salts and organic molecules on the aerosol surface. A series of experiments with varying salts reveal how different ions influence the partitioning behavior of organic molecules, underscoring the importance of ionic species in governing aerosol surface dynamics. The final part of the study reveals a significant difference between the aerosol and planar air-water interfaces. The equilibrium rate constant for aerosols is found to be tenfold faster, indicating a larger Gibbs free energy, contrasting with the planar air-water interface scenario. And aerosol surfaces exhibit lower molecular density due to the finite availability of organic molecules. These findings highlight aerosol surfaces' unique kinetic and thermodynamic behaviors compared to their planar counterparts. This work significantly advances our understanding of aerosols, their surfaces, and the various factors influencing their behavior in the atmosphere. The findings have crucial implications for our comprehension of climate change, air quality, and aerosols' environmental and health impacts. The introduction of a novel in-situ technique for detecting organic molecules at aerosol surfaces marks a breakthrough in aerosol research, offering insights into the distribution and interactions of these molecules within atmospheric particles. / Chemistry