AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Role of Semi- and Low-Volatile Organic Compounds and Particle Phase Processes in Nanoparticle Growth - a Modeling Study
TAINA YLI-JUUTI, Ilona Riipinen, Ulrich Poeschl, Manabu Shiraiwa, University of Eastern Finland
Abstract Number: 387 Working Group: Aerosol Chemistry
Abstract The climatic effects of atmospheric secondary aerosol particles depend on how many of the freshly formed nanometer sized particles grows enough large to act as cloud condensation nuclei instead of being scavenged by coagulation. Atmospheric nanoparticle growth is largely due to uptake of organic and inorganic trace gases, organics often being major contributors. To contribute to nanoparticle mass significantly, the organics need to be low-volatile and uptake of organic compounds on aerosol particles can be divided roughly in two: condensation of low-volatile organic compounds (LVOC) formed in the gas phase and uptake of gas phase semi-volatile organic compounds (SVOC) followed by production of LVOCs in the particle phase or at the particle surface. This study aims at identifying the groups of organic compounds and the processes that are important for atmospheric nanoparticle growth. The focus is on four processes: salt formation and oligomerization in the particle phase, condensation of LVOCs and particle phase mass transport which can affect the particle phase reactions.
We studied the processes using a newly developed particle growth model KM-GAP-T (KM-GAP with Thermodynamics) which combines the detailed kinetics of mass transport in and between gas phase, particle surface and particle bulk with the thermodynamics of particle phase acid-base chemistry. The model simulations were designed to represent boreal forest environment and condensing vapors included sulfuric acid, ammonia, water and organic model compounds representing organic acids, SVOCs that can form oligomers in the particle phase (two model compounds), and LVOCs. Based on the simulations we found that condensation of LVOCs is important, especially at the smallest particle sizes. Oligomerization may contribute to the growth if the reaction rate of SVOCs is high, e.g. due to acidity of the particles at low base concentrations, and organic salt formation may be important at elevated base concentrations.