1Department of Physics, University of Kuopio, Kuopio, 70211, Finland
2Department of Environmental Sciences, University of Kuopio, Kuopio, 70211, Finland
3Department of Physics, P.O box 68, University of Helsinki, Helsinki, 00014, Finland
4Aerodyne Research, Inc., Billerica, MA 08121-3976, USA
5Finnish Meteorological Institute, Helsinki, 00101, Finland
6Atmospheric Chemistry Division, National Center for Atmospheric Res., 1850 Table Mesa Dr., Boulder, CO, 80305, USA
7Finnish Meteorological Institute, Kuopio, 70211, Finland
*now also at: Dept. of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge MA, USA
Received: 11 Mar 2009 – Discussion started: 27 Mar 2009
Abstract. Measurements of particle formation following the gas phase oxidation of volatile organic compounds (VOCs) emitted by Scots pine (Pinus sylvestris L.) seedlings are reported. Particle formation and condensational growth both from ozone (O3) and hydroxyl radical (OH) initiated oxidation of pine emissions (about 20-120 ppb) were investigated in a smog chamber. During experiments, tetramethylethylene (TME) and 2-butanol were added to control the concentrations of O3 and OH. Particle formation and condensational growth rates were interpreted with a chemical kinetic model. Scots pine emissions mainly included α-pinene, β-pinene, Δ3-carene, limonene, myrcene and β-phellandrene, composing more than 95% of total emissions. Modeled OH concentrations in the O3- and OH-induced experiments were on the order of ~106 molecules cm−3. Our results demonstrate that OH-initiated oxidation of VOCs plays an important role in the nucleation process during the initial new particle formation stage. The highest average particle formation rate of 360 cm−3 s−1 was observed for the OH-dominated nucleation events and the lowest formation rate of less than 0.5 cm−3 s−1 was observed for the case with only O3 present as an oxidant. In contrast to the particle formation process, ozonolysis of monoterpenes appears to be much more efficient to the aerosol growth process following nucleation. Higher contributions of more oxygenated products to the SOA mass loadings from OH-dominated oxidation systems were found as compared to the ozonolysis systems. Comparison of mass and volume distributions from the aerosol mass spectrometer and differential mobility analyzer yields estimated SOA effective densities of 1.34±0.06 g cm−3 for the OH+O3 oxidation systems and 1.38±0.03 g cm−3 for the O3 dominated chemistry.
Revised: 26 Sep 2009 – Accepted: 02 Oct 2009 – Published: 28 Oct 2009
Hao, L. Q., Yli-Pirilä, P., Tiitta, P., Romakkaniemi, S., Vaattovaara, P., Kajos, M. K., Rinne, J., Heijari, J., Kortelainen, A., Miettinen, P., Kroll, J. H., Holopainen, J. K., Smith, J. N., Joutsensaari, J., Kulmala, M., Worsnop, D. R., and Laaksonen, A.: New particle formation from the oxidation of direct emissions of pine seedlings, Atmos. Chem. Phys., 9, 8121-8137, doi:10.5194/acp-9-8121-2009, 2009.