Why ozonolysis may not increase the hydrophilicity of particles |
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| Authors: | T.M. McIntire O.S. Ryder P.L. Gassman Z. Zhu S. Ghosal B.J. Finlayson-Pitts |
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| Affiliation: | 1. Department of Chemistry, University of California, Irvine, CA 92697-2025, USA;2. Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352, USA;3. Lawrence Livermore National Laboratory, Livermore, CA 94551, USA;1. Institute of Functional Nanomaterials, University of Puerto Rico, San Juan, PR 00931, USA;2. Department of Physics, University of Puerto Rico, PO Box 70377, San Juan, PR 00936, USA;3. Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439, USA;4. Department of Chemistry, University of Puerto Rico, San Juan, PR 00936, USA;1. Institute of Catalysis, Novosibirsk 630090, Russia;2. Institute of Biochemistry, Novosibirsk 630117, Russia;1. Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science & Technology, Nanjing 210044, China;2. Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, Nanjing University of Information Science & Technology, Nanjing 210044, China;1. Materials Chemistry and Analysis Group, Department of Chemistry and Tyndall National Institute, University College Cork, Cork, Ireland;2. Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin, Dublin 2, Ireland;3. Central Fabrication Facility, Tyndall National Institute, Lee Maltings, Dyke Parade, Ireland;4. Silicon Research Group, Tyndall National Institute, Lee Maltings, Dyke Parade, Ireland;5. Nanostructured Materials & Devices Group, Department of Chemistry, Imperial College London, London, UK;1. Nano-Science Center, Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark;2. Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland;1. State Key Laboratory of Chemical Engineering, Department of Chemistry, Zhejiang University, Hangzhou 310027, China;2. Key Lab of Applied Chemistry of Zhejiang Province, Department of Chemistry, Zhejiang University, China;3. Institute of Chemical Biology and Pharmaceutical Chemistry, Zhejiang University, China |
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| Abstract: | It is commonly assumed that atmospheric oxidation of hydrocarbon particles or hydrocarbon coatings on particles leads to polar products and increased water uptake, altering atmospheric visibility and increasing the likelihood they will act as cloud condensation nuclei (CCN). We show here through laboratory experiments that increased water uptake depends on the 3-dimensional structure of the particles. Laboratory studies of particles formed during ozonolysis of surface-bound alkenes, present as terminally unsaturated self-assembled monolayers (C8= SAM) on a silica substrate, were carried out at room temperature and 1 atm pressure. SAMs were exposed to ～1013 O3 molecules cm?3 for 40 min and resultant particles were analyzed using single particle Fourier transform infrared micro-spectroscopy (micro-FTIR) and secondary ion mass spectroscopy (SIMS). Spectroscopy results show that –COOH and other polar groups are formed but are buried inside a hydrophobic shell, consistent with earlier observations (McIntire et al., 2005, Moussa et al., 2009) that water uptake does not increase after reaction of the terminal alkene with O3. These insights into the 3-D structure of particles formed on oxidation have important implications for the ability of secondary organic aerosols to act as CCN. In addition, the nature of the surface of the particles is expected to determine their uptake into biological systems such as the surface of the lungs. |
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