AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Resolving Size-dependent Particle Growth Rates below 2 nm from the Particle Size Magnifier
Katrianne Lehtipalo, Siegfried Schobesberger, Alessandro Franchin, Tuomo Nieminen, Juha Kangasluoma, Jenni Kontkanen, JYRI MIKKILÄ, Tuukka Petäjä, Markku Kulmala, University of Helsinki
Abstract Number: 690 Working Group: Aerosol Nucleation: From Clusters to Nanoparticles
Abstract The molecular level processes leading to new particle formation are not yet completely understood, mainly due to difficulties in detecting the smallest neutral clusters and particles. New kinds of condensation particle counters allow deriving the formation and growth rates directly from measurements also in the size range below 2 nm, which is the size critical for nucleation.
The Airmodus A09 Particle Size Magnifier (PSM) was used to resolve the size distribution of particles below 2 nm. The growth rates (GR) were calculated from the difference between the appearance times of the newly formed particle population with different cut-off sizes of the scanning PSM. The method was used to for example to nucleation experiments in the CLOUD-chamber and for field measurements at the Hyytiälä SMEAR II measurement station . The growth rates were also compared to the growth of charged sulphuric acid clusters measured with the APi-TOF mass spectrometer, and to the growth rates of 1.6-3 nm ions derived from ion spectrometers. However, the PSM gives additional information on the behaviour of the smallest neutral particles at the beginning of the new particle formation process. This is crucial since nucleation in the boundary layer is most probably dominated by neutral mechanisms. The initial growth rates determine what fraction of the newly formed particles eventually reach sizes, where they can act as CCN and influence the climate.