Laboratory experiments are conducted to investigate aging of size-classified black carbon (BC)particles from OH-initiated oxidation of m-xylene.The variations in the particle size, mass, effective density, morphology, optical properties, hygroscopicity, and activation as cloud condensation nuclei (CCN)are simultaneously measured by a suite of aerosol instruments, when BC particles produced from incomplete combustion of propane are exposed to the oxidation products of the OH-m-xylene reactions.