Articles | Volume 13, issue 4
Atmos. Chem. Phys., 13, 2283–2297, 2013
Atmos. Chem. Phys., 13, 2283–2297, 2013

Research article 27 Feb 2013

Research article | 27 Feb 2013

CCN activity and volatility of β-caryophyllene secondary organic aerosol

M. Frosch1,*, M. Bilde1, A. Nenes2,3, A. P. Praplan4,**, Z. Jurányi4,***, J. Dommen4, M. Gysel4, E. Weingartner4, and U. Baltensperger4 M. Frosch et al.
  • 1Department of Chemistry, University of Copenhagen, Copenhagen, Denmark
  • 2School of Earth {&} Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
  • 3School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USA
  • 4Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland
  • *now at: Division of Nuclear Physics, University of Lund, Lund, Sweden
  • **now at: Division of Atmospheric Sciences, Department of Physics, University of Helsinki, Helsinki, Finland
  • ***now at: School of Engineering, Institute of Aerosol and Sensor Technology, University of Applied Sciences Northwestern Switzerland, Windisch, Switzerland

Abstract. In a series of smog chamber experiments, the cloud condensation nuclei (CCN) activity of secondary organic aerosol (SOA) generated from ozonolysis of β-caryophyllene was characterized by determining the CCN derived hygroscopicity parameter, κCCN, from experimental data. Two types of CCN counters, operating at different temperatures, were used. The effect of semi-volatile organic compounds on the CCN activity of SOA was studied using a thermodenuder.

Overall, SOA was only slightly CCN active (with κCCN in the range 0.001–0.16), and in dark experiments with no OH scavenger present, κCCN decreased when particles were sent through the thermodenuder (with a temperature up to 50 °C).

SOA was generated under different experimental conditions: In some experiments, an OH scavenger (2-butanol) was added. SOA from these experiments was less CCN active than SOA produced in experiments without an OH scavenger (i.e. where OH was produced during ozonolysis). In other experiments, lights were turned on, either without or with the addition of HONO (OH source). This led to the formation of more CCN active SOA.

SOA was aged up to 30 h through exposure to ozone and (in experiments with no OH scavenger present) to OH. In all experiments, the derived κCCN consistently increased with time after initial injection of β-caryophyllene, showing that chemical ageing increases the CCN activity of β-caryophyllene SOA. κCCN was also observed to depend on supersaturation, which was explained either as an evaporation artifact from semi-volatile SOA (only observed in experiments lacking light exposure) or, alternatively, by effects related to chemical composition depending on dry particle size.

Using the method of Threshold Droplet Growth Analysis it was also concluded that the activation kinetics of the SOA do not differ significantly from calibration ammonium sulphate aerosol for particles aged for several hours.

Final-revised paper