Noval Experimental Techniques for the physical and chemical characterization of Nucleation mode Aerosol Particles
Final Report Abstract
This project explored innovative experimental techniques for the analysis of nucleation mode aerosol particles (less than 30 nm in diameter) for an improved understanding of secondary aerosol formation, and the direct quantification of turbulent aerosol fluxes in the lower atmospheric boundary layer. For the chemical analysis of nucleation mode aerosol particles, a new field-portable aerosol mass spectrometer, the so-called Chemical Analyzer for Charged Ultrafine Particles (CAChUP) has been successfully developed, and applied in flow tube experiments of new particle formation from alphapinene ozonolysis. The limit of detection for secondary organic aerosol from alpha-pinene ozonolysis was found to be below 2.1 – 2.6 ng. Presently, this is one of only three aerosol mass spectrometers available worldwide for in-situ measurements of the chemical composition of sub-30 nm aerosol particles in laboratory and field experiments. In the field, a neutral cluster and air ion spectrometer was used to investigate the role of ions in new particle formation events. A detailed analysis of the concentration patterns and growth dynamics of positive/negative ions and neutral clusters and particles in the mobility diameter range from 2 – 25 nm revealed several unexpected results: In new particle formation events, the concentration of 2 nm ions typically began to increase 20 – 30 min before the concentration of 2 nm neutral clusters. The time difference between the ion mode and the neutral mode decreased during particle growth and vanished when diameters of 15 – 20 nm were reached. This observation is consistent with higher growth rates of neutral particles compared to ions, and can be explained conceptually when taking into account the recombination and attachment of cluster ions, which are constantly present. Meanwhile, these specific growth dynamics of ions and neutral particles have also been found at various other sites in Europe, e.g. Melpitz (Germany), Puy de Dôme (France), and Jungfraujoch (Switzerland) during new particle formation events. Aerosol flux measurements were carried out with a new fast condensation particle counter resolving fluctuations of the aerosol number concentration with a resolution better than 10 Hz. In two field campaigns, the fast condensation particle counter was used in an eddy covariance measurement setup to quantify the turbulent exchange of aerosol particles between the surface and the atmosphere at a forest clearing and above a Norway spruce stand. Spectral analysis revealed that high frequency contributions to aerosol fluxes can be directly resolved with the fast condensation particle counter, while commercial condensation particle counters cannot do so and require flux corrections. Therefore, the measurement results obtained in this project are valuable for testing post-processing routines that correct for high frequency losses of particle counters used in aerosol flux measurements. Overall, the project succeeded in establishing and applying innovative experimental techniques for the analysis of physical and chemical properties of atmospheric aerosol particles with diameters of less than 30 nm. These experimental techniques will also contribute to future studies of secondary aerosol formation and help to elucidate the turbulent transport and chemical processing of atmospheric aerosol particles.
Publications
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(2012) Characterization of a thermal desorption mass spectrometer for freshly nucleated secondary aerosol particles. Proceedings of the European Aerosol Conference 2012, Granada, Spain
Gonser, S.G., Held, A.
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(2013) A chemical analyzer for charged ultrafine particles. Atmos. Meas. Tech. 6, 2339-2348
Gonser, S.G., Held, A.
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(2013) Mass spectrometry of freshly nucleated secondary organic aerosol from flow reactor experiments. Faraday Discussions FD165, 22 – 24 July, 2013, University of Leeds, United Kingdom
Held, A., Gonser, S.G.
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(2014) Ion dynamics and aerosol mass spectrometry during atmospheric new particle formation. Dissertation, Universität Bayreuth, Fakultät für Biologie, Chemie und Geowissenschaften, 129 pp.
Gonser, S.G.
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(2014) Ion – particle interactions during particle formation and growth at a coniferous forest site in central Europe. Atmos. Chem. Phys. 14, 10547-10563
Gonser, S.G., Klein, F., Birmili, W., Größ, J., Kulmala, M., Manninen, H.E., Wiedensohler, A., Held, A.
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(2014) Spectral analysis of turbulent aerosol fluxes by Fourier transform,wavelet analysis, and multiresolution decomposition. Boundary-Layer Meteorol 151, 79-94
Held, A.
