American Association for Aerosol Research - Abstract Submission

AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA

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The Role of Organic Condensation on Ultrafine Particle Growth during Nucleation Events

DAVID PATOULIAS, Ilona Riipinen, Spyros Pandis, University of Patras, Greece

     Abstract Number: 193
     Working Group: Carbonaceous Aerosols in the Atmosphere

Abstract
The ultrafine particles can grow to larger sizes and become cloud condensation nuclei (CCN) affecting cloud reflectivity and lifetime. This indirect effect is thus perturbing the energy balance of the planet. We applied an updated box model version of the Dynamic Model for Aerosol Nucleation in order to simulate the nucleation and subsequent growth in a remote continental location, Hyytiala, Finland. The individual effects of various processes and parameters on aerosol growth were quantified. DMAN uses the Two-Moment Aerosol Sectional algorithm to track both aerosol number and mass concentration using a sectional approach and describes both coagulation and condensation (sulfate, ammonium, organics). Our approach combines the SAPRC-99 mechanism for gas-phase chemistry and the 1-D the volatility basis set framework (VBS) for secondary organic aerosol formation and OA chemical aging.

The surface energy of the condensing organics has as a significant effect on the ultrafine particle rate. For a typical spring nucleation episode, an increase of the assumed surface energy results in a decrease of the particle number concentration above 3 nm (N3) but it increases the number concentration above 100 nm (N100). On the other hand the different parameterizations of the secondary OA chemical aging have a small effect on N3 but can have a major effect on N100.

The model reproduces the observed onset of nucleation and the qualitative features of the event. The particle growth is reproduced well by comparison with measurements.The simulation suggests that while sulfuric acid plays an important role of nucleation of new particles, it is not responsible for most of their growth, a finding consistent with the analysis of field observations in the site. The semivolatile-SOA produced upon oxidation of biogenic volatile organic compounds (BVOCs) is a key player for the later stages of growth.