We present chemical observations of newly formed particles as small as ~10 nm from new particle formation experiments using sulfuric acid, dimethylamine, ammonia, and water vapor as gas phase reactants. The nanoparticles were more acidic than expected based on thermodynamic expectations, particularly at the smallest measured sizes. The results indicate rapid surface conversion of SO2
to sulfate under the high SO2
experimental conditions and the existence of a phase change near this size.