The goal of the project is to elucidate the processes and cause-and-effect relationships between aerosols, cloud physics and precipitation by making measurements of the physical, chemical, optical and cloud nucleating properties of aerosols on the NOAA research vessel Ronald H Brown (RHB) during the VOCALS-REx (VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment). The research focuses on measurement of aerosol parameters relevant to cloud condensation nuclei and cloud droplet formation in subtropical stratocumulus that are modulated by cloud processes especially drizzle and coalescence scavenging. Physical measurements will include number-size distribution from 3 nm to 10 ?�m diameter using mobility separation, condensation particle counting, aerodynamic particle sizing and impactor sampling from 0.1 to 10?�m. Chemical analysis will include 7- and 2-stage impactor sampling (above and below 1 ?�m), analysis for major inorganic ions via ion chromatography (IC), trace metals via XRF, and organic and elemental carbon via optical and evolved carbon thermography. Sub-?�m particles will be analyzed for inorganic ions by particle into liquid sampling (PILS) and IC. Cloud condensation nuclei (CCN) at supersaturations from 0.2% to 2% will be measured with a continuous flow, thermal gradient CCN counter. Aerosol optical parameters, light scattering and absorption, will be determined by nephelometry and filter based absorption, respectively, at three visible wavelengths for sub-10?�m and sub-1?�m size ranges at 60% relative humidity. The dependence of scattering on RH will be determined for the sub-1?�m range between 25% and 85% RH. The size distribution, PILS IC, optical parameters and CCN will have a time resolution of 15 minutes or less; impactor-based chemistry will have 6 to 12 hour resolution. Our measurements will be coordinated with others on the ship, e.g. gas phase, flux, cloud radar, lidar. They will also be coordinated with aerosol measurements on other platforms, e.g. NSF/NCAR C130, UNOLS ship Wecoma and ONR Twin Otter aircraft, including near-proximity platform intercomparisons. The data will be analyzed in the context of meteorological and oceanographic data to investigate the processes and cause-effect relationships between aerosols, cloud physics and precipitation. Because of interactions that are thought to occur in this system, determining these relations will require integration of the data with other observations and the modeling community. Analysis products will provide input to the VOCALS modeling community (VOCALS-Mod) and the wider community for scales from LES to GCMs. Multivariate statistical analysis will be used to determine relationships between aerosol parameters (e.g., concentration, size distribution, composition) and cloud physics parameters, (e.g., cloud albedo and effective radius, vertical mixing, cloud base, top and precipitation rate).