AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Model for Acid-Base Chemistry in Nanoparticle Growth
TAINA YLI-JUUTI, Kelley C. Barsanti, Lea Hildebrandt Ruiz, Antti-Jussi Kieloaho, Theo Kurten, Ulla Makkonen, Tuukka Petäjä, Mikko Äijälä, Markku Kulmala, Ilona Riipinen, University of Helsinki
Abstract Number: 116 Working Group: Aerosol Chemistry
Abstract The climatic effects of particles formed in gas-to-particle phase transformation depend on how fast they grow relative to how quickly they are scavenged by larger particles. Sulphuric acid is found to be the key compound in atmospheric nucleation but its contribution to nanoparticle growth is estimated to be small in many environments. The observations on atmospheric nanoparticle growth suggest that a large fraction of the growth is due to condensation of organic vapors, although the exact identification of these vapors as well as the mechanisms related to the growth are still unknown. To condense on atmospheric nanoparticles organic vapors must have very low-volatility. While reversible condensation requires a very low saturation vapor pressure, particle phase processes like salt formation may also enable compounds with higher saturation vapor pressures to contribute to particle growth. Recently, evidence for the presence of organic salts in atmospheric nanoparticles has been observed.
We studied the potential contribution of organic and inorganic salt formation on particle growth rates using our newly developed model for acid-base chemistry in nanoparticle growth. This single particle model combines a dynamical condensation model for calculating the mass fluxes of vapors to a particle and an equilibrium thermodynamic model (Extended Aerosol Inorganic Model, E-AIM) for calculating the particle phase dissociation of acids and bases, including calculation of activity coefficients. We applied the model for an atmospherically relevant system consisting of two acids (sulphuric acid and an organic acid), two bases (ammonia and an amine) and water. Using the model we studied the potential effect of particle phase salt formation on the growth rates of individual particles in various ambient conditions, as well as the relative contributions of chemically distinct acids and bases. We will discuss the results in the context of atmospheric particle growth rates and their observed size dependence.