Nanoparticle Growth by Particle Phase Chemistry

Abstract. The ability of particle phase chemistry to alter the molecular composition and enhance the growth rate of nanoparticles in the 2–100 nm diameter range is investigated through the use of a growth model. The molecular components included are sulfuric acid, ammonia, water, a non-volatile organic compound and a semi-volatile organic compound. Molecular composition and growth rate are compared for particles that grow by partitioning alone vs. those that grow by a combination of partitioning and an accretion reaction in the particle phase between two organic molecules. Particle phase chemistry causes a change in molecular composition that is particle diameter dependent, and when the reaction involves semi-volatile molecules, the particles grow faster than by partitioning alone. These effects are most pronounced for particle larger than about 20 nm in diameter. The growth rate enhancement increases linearly with increasing particle diameter and is dependent on the gas phase mixing ratio of the semi-volatile reactant and the reaction rate constant. The results are discussed in the context of recent experimental measurements of particle size-dependent molecular composition and the relationship between accretion product formation and cloud condensation nuclei (CCN) activity.