HR: 1340h
AN: A23B-1261    [Abstracts]
TI: The cloud forming potential of secondary organic aerosol under near atmospheric conditions
AU: * duplissy, J
EM: jonathan.duplissy@psi.ch
AF: Paul Scherrer Institut, Laboratory of atmospheric chemistry, Villigen PSI ost, 5232, Switzerland
AU: Gysel, M
EM: martin.gysel@psi.ch
AF: Paul Scherrer Institut, Laboratory of atmospheric chemistry, Villigen PSI ost, 5232, Switzerland
AU: Rami, A
EM: rami.alfarra@psi.ch
AF: Paul Scherrer Institut, Laboratory of atmospheric chemistry, Villigen PSI ost, 5232, Switzerland
AU: Dommen, J
EM: Josef.dommen@psi.ch
AF: Paul Scherrer Institut, Laboratory of atmospheric chemistry, Villigen PSI ost, 5232, Switzerland
AU: Metzger, A
EM: axel.metzger@psi.ch
AF: Paul Scherrer Institut, Laboratory of atmospheric chemistry, Villigen PSI ost, 5232, Switzerland
AU: Prévot, A
EM: andre.prevot@psi.ch
AF: Paul Scherrer Institut, Laboratory of atmospheric chemistry, Villigen PSI ost, 5232, Switzerland
AU: Weingartner, E
EM: ernest.weingartner@psi.ch
AF: Paul Scherrer Institut, Laboratory of atmospheric chemistry, Villigen PSI ost, 5232, Switzerland
AU: Laaksonen, A
EM: alaakson@messi.uku.fi
AF: Department of Physics, University of Kuopio P.O. Box 1627, Kuopio, 70211, Finland
AU: Raatikainen, T
EM: tomi.raatikainen@fmi.fi
AF: Finnish Meteorological Institute, P.O. Box 503, Helsinki, 00101, Finland
AU: Good, N
EM: nicholas.a.good@stud.man.ac.uk
AF: Centre for Atmospheric Sciences, University of Manchester, PO Box 88, Sackville Street, Manchester, M60 1QD, United Kingdom
AU: Turner, F
EM: fiona.turner@manchester.ac.uk
AF: Centre for Atmospheric Sciences, University of Manchester, PO Box 88, Sackville Street, Manchester, M60 1QD, United Kingdom
AU: McFiggans4, G
EM: gordon.mcfiggans@manchester.ac.uk
AF: Centre for Atmospheric Sciences, University of Manchester, PO Box 88, Sackville Street, Manchester, M60 1QD, United Kingdom
AU: Baltensperger, U
EM: urs.baltensperger@psi.ch
AF: Paul Scherrer Institut, Laboratory of atmospheric chemistry, Villigen PSI ost, 5232, Switzerland
AB: Cloud formation occurs through droplet nucleation by ever-present atmospheric aerosol particles. Atmospheric aerosol populations invariably contain organic material, and photo-oxidation of biogenically emitted volatile organic compounds (VOCs) to form secondary organic aerosol (SOA) is widely considered a major contribution to the organic fraction. Smog chambers are used to investigate the formation and evolution of SOA particles and the potential effect on cloud formation of changes in particle size, composition, and surface tension. High concentrations of VOCs are commonly used to improve measurements statistics in chamber studies. Here we demonstrate for the first time that lower precursor concentrations are necessary for a lower aerosol mass yield, with atmospherically representative particle composition, hygroscopicity, and cloud formation potential. Furthermore, by probing cloud activation behaviour, we show that the supersaturation required to activate particles decreases with particle age at a given size. This demonstrates that composition plays a role in cloud droplet formation as well as size. We also demonstrate that a semi-empirical approach can be accurately used to calculate critical supersaturation of SOA particles from the measured hygroscopic growth below 100% RH and, based on an extensive sensitivity study, conclude that the surface tension of the SOA solution at the droplet size of activation differs minimally from that of pure water. Thus, at critical supersaturation SOA does not significantly contribute to the reduction in surface tension attributed to the organic aerosol, with important implications for cloud formation and climate.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting