1Center for Atmospheric Particle Studies (CAPS), Carnegie Mellon University, 15213, Pittsburgh, PA, USA
2Department of Physics, University of Helsinki, 00014, Helsinki, Finland
3Department of Physics and Atmospheric Science, Dalhousie University, B3H 3J5, Halifax, NS, Canada
4Department of Chemistry, University of Toronto, M5S 3H6, Toronto, ON, Canada
5Science and Technology Branch, Environment Canada, M3H 5T4, Toronto, ON, Canada
6Finnish Meteorological Institute, 00880, Helsinki, Finland
7Aerodyne Research Inc., 01821, Billerica, MA, USA
8Institute of Chemical Engineering and High Temperature Processes (ICE-HT) Foundation for Research & Technology, Hellas (FORTH), 26504, Patra, Greece
*now at: Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
Received: 10 Dec 2010 – Published in Atmos. Chem. Phys. Discuss.: 06 Jan 2011
Abstract. Atmospheric aerosol particles influence global climate as well as impair air quality through their effects on atmospheric visibility and human health. Ultrafine (<100 nm) particles often dominate aerosol numbers, and nucleation of atmospheric vapors is an important source of these particles. To have climatic relevance, however, the freshly nucleated particles need to grow in size. We combine observations from two continental sites (Egbert, Canada and Hyytiälä, Finland) to show that condensation of organic vapors is a crucial factor governing the lifetimes and climatic importance of the smallest atmospheric particles. We model the observed ultrafine aerosol growth with a simplified scheme approximating the condensing species as a mixture of effectively non-volatile and semi-volatile species, demonstrate that state-of-the-art organic gas-particle partitioning models fail to reproduce the observations, and propose a modeling approach that is consistent with the measurements. We find that roughly half of the mass of the condensing mass needs to be distributed proportional to the aerosol surface area (thus implying that the condensation is governed by gas-phase concentration rather than the equilibrium vapour pressure) to explain the observed aerosol growth. We demonstrate the large sensitivity of predicted number concentrations of cloud condensation nuclei (CCN) to these interactions between organic vapors and the smallest atmospheric nanoparticles – highlighting the need for representing this process in global climate models.
Revised: 12 Apr 2011 – Accepted: 13 Apr 2011 – Published: 27 Apr 2011
Riipinen, I., Pierce, J. R., Yli-Juuti, T., Nieminen, T., Häkkinen, S., Ehn, M., Junninen, H., Lehtipalo, K., Petäjä, T., Slowik, J., Chang, R., Shantz, N. C., Abbatt, J., Leaitch, W. R., Kerminen, V.-M., Worsnop, D. R., Pandis, S. N., Donahue, N. M., and Kulmala, M.: Organic condensation: a vital link connecting aerosol formation to cloud condensation nuclei (CCN) concentrations, Atmos. Chem. Phys., 11, 3865-3878, doi:10.5194/acp-11-3865-2011, 2011.