AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Size-Dependent Condensation of Organics – Parameterization for Nanoparticle Growth
SILJA HÄKKINEN, Hanna Manninen, Taina Yli-Juuti, Joonas Merikanto, Maija Kajos, Tuomo Nieminen, Stephen D'Andrea, Ari Asmi, Jeffrey Pierce, Markku Kulmala, Ilona Riipinen, University of Helsinki
Abstract Number: 58 Working Group: Aerosol Physics
Abstract One of the biggest challenges in current large-scale atmospheric models is to accurately present nanoparticle growth by biogenic and anthropogenic secondary organics. Accurate estimation of atmospheric nanoparticle growth is important in order to improve the prediction of the concentrations of cloud condensation nuclei (CCN). In our work we introduce a semi-empirical parameterization of size-dependent sub-20 nm particle growth that distributes atmospheric organics to nanoparticles according to their size. The parameterization includes particle condensational growth by sulfuric acid, secondary organics from monoterpene oxidation (SORG$_(MT)) and an additional condensable non-monoterpene organics (“background”). Nanoparticle growth in three size classes, 1.5 to 3 nm, 3 to 7 nm and 7 to 20 nm, was investigated. The performance of the parameterization as well as the experimental parameters (weighting factors for distributing the SORG$_(MT) and the concentration of the background species) for the parameterization were determined using extensive field data obtained from six temperate continental European sites. In our analysis there were altogether 7 years of data from Hyytiälä (Finland) and around one year of data from other measurement stations. The parameterization was able to reproduce the observed nanoparticle growth rates and to capture the seasonal pattern observed in the ambient nanoparticle growth. The contribution of SORG$_(MT) to nanoparticle growth was strongly dependent on particle size – weighting factors for distributing SORG$_(MT) were 0 for the smallest particles (1.5 to 3 nm) and approaching 1 for the 7 to 20 nm particles. The contribution of the background species was also important, especially for the very smallest particles, its concentration being similar to that of the SORG$_(MT) and sulfuric acid. The “background” is suggested to be formed in the oxidation process of biogenic organics in the presence of anthropogenic pollution.