Elemental composition and clustering behaviour of α-pinene oxidation products for different oxidation conditions
- 1Department of Physics, P.O. Box 64, 00014 University of Helsinki, Helsinki, Finland
- 2Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
- 3Institute for Atmospheric and Climate Science, ETH Zurich, 8092 Zurich, Switzerland
- 4Laboratory for Systems, Instrumentation, and Modeling in Science and Technology for Space and the Environment (SIM), University of Lisbon and University of Beira Interior, 1749-016 Lisbon, Portugal
- 5Helsinki Institute of Physics, University of Helsinki, Helsinki, Finland
- 6University of Innsbruck, Institute for Ion Physics and Applied Physics, Technikerstrasse 25, 6020 Innsbruck, Austria
- 7Ionicon Analytik, Eduard Bodem Gasse 3, 6020 Innsbruck, Austria
- 8Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt am Main, Altenhöferallee 1, 60438 Frankfurt am Main, Germany
- 9CERN, CH1211, Geneva, Switzerland
- 10Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna, Austria
- 11Center for Atmospheric Particle Studies, Carnegie Mellon University, 5000 Frobes Ave, Pittsburgh, PA 15213, USA
- 12Aerodyne Research Incorporated, Billerica, MA 01821, USA
- *now at: University of Washington, Department of Atmospheric Sciences, Box 351640, Seattle, WA 98195, USA
Abstract. This study presents the difference between oxidised organic compounds formed by α-pinene oxidation under various conditions in the CLOUD environmental chamber: (1) pure ozonolysis (in the presence of hydrogen as hydroxyl radical (OH) scavenger) and (2) OH oxidation (initiated by nitrous acid (HONO) photolysis by ultraviolet light) in the absence of ozone.
We discuss results from three Atmospheric Pressure interface Time-of-Flight (APi-TOF) mass spectrometers measuring simultaneously the composition of naturally charged as well as neutral species (via chemical ionisation with nitrate). Natural chemical ionisation takes place in the CLOUD chamber and organic oxidised compounds form clusters with nitrate, bisulfate, bisulfate/sulfuric acid clusters, ammonium, and dimethylaminium, or get protonated. The results from this study show that this process is selective for various oxidised organic compounds with low molar mass and ions, so that in order to obtain a comprehensive picture of the elemental composition of oxidation products and their clustering behaviour, several instruments must be used. We compare oxidation products containing 10 and 20 carbon atoms and show that highly oxidised organic compounds are formed in the early stages of the oxidation.