Atmospheric aerosol particles were collected over three field experiments in the remote and coastal marine boundary layer of the eastern Pacific Ocean from aircraft, ship, and stationary platforms and were analyzed using Fourier Transform Infrared (FTIR) spectroscopy, Aerosol Mass Spectrometry (AMS), and Scanning Transmission X-ray Microscopy with Near-Edge Absorption Fine Structure (STXM-NEXAFS) for organic functional groups and organic mass fragments. X-ray uorescence (XRF) and Scanning Electron Microscopy with Energy Dispersive X-rays (SEM-EDX) analyses were used to investigate the elemental composition of the analyzed particles. The aim of these studies was to better characterize particle sources and composition in the stratocumulus-topped marine boundary layer (MBL), where aerosol-cloud interactions play an important role in controlling the reflectivity of the large cloud decks. Particle composition was linked to distinct particle sources including primary marine emissions, biomass burning, and fossil fuel combustion. Fossil fuel combustion particles were characterized by large contributions from saturated alkane and carboxylic acid groups. Biomass burning aerosol particles were characterized as mixtures of alkane, carboxylic acid, and ketone groups, consistent with biogenic secondary organic aerosol particles observed in chamber studies. Photochemical aging of the transported smoke particles was observed on diurnal and multi-day timescales as an increase in the relative amount of oxygenated groups and oxygen-containing molecular fragments. Marine primary organic aerosol (POA) particles were observed in shipboard samples and were characterized by large contributions from organic hydroxyl groups, suggesting a carbohydrate-containing source in the ocean surface emitted during bubble bursting. Marine particles were also identified in single particle STXM-NEXAFS and were classified into four distinct categories including soluble and insoluble polysaccharides, proteins, and calcareous phytoplankton fragments. The presence of oxidized (polar) organic components—ketone, organic hydroxyl, and carboxylic acid groups—in submicron particles suggests that many of the measured particles could contribute to cloud condensation nuclei number concentration and mass in both open ocean and coastal regions. Together, these measurements show that marine POA provides a significant contribution to submicron particle mass in the clean MBL, whereas fossil fuel combustion and biomass burning emissions contribute the majority of the organic mass in coastal regions.