Environmental scanning electron microscopy as a new technique to determine the hygroscopic behaviour of individual aerosol particles |
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| Authors: | Martin Ebert Marion Inerle-Hof Stephan Weinbruch |
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| Institution: | 1. Bauman Moscow State Technical University, 105005, 2nd Baumanskaya str. 5, Moscow, Russia;2. National Research University “Moscow Power Engineering Institute”, 111250, Krasnokazarmennaya str. 14, Moscow, Russia;1. Department of Mechanical Engineering, University of Alberta, Edmonton, Canada;2. Department of Mechanical Engineering, University of British Columbia, Vancouver, Canada;3. Metrology Research Centre, National Research Council Canada, Ottawa, Canada;1. Division of Environment, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China;2. Department of Chemistry, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China;1. Department of Chemistry & Chemical Biology, McMaster University, Hamilton, Ontario, L8S 4L8, Canada;2. Department of Chemical Engineering, McMaster University, Hamilton, Ontario, L8S 4L8, Canada;3. Centre of Excellence in Protective Equipment and Materials, McMaster University, Hamilton, Ontario, L8S 4L8, Canada;4. Department of Medicine, McMaster University, Hamilton, Ontario, L8S 4L8, Canada;5. Department of Medicine, St Joseph''s Healthcare Hamilton, Hamilton, Ontario, L8N 4A6, Canada;6. Department of Health Research, Evidence, and Impact, McMaster University, Hamilton, Ontario, L8S 4L8, Canada;7. Aerosol and Gas Metrology, Metrology Research Centre, National Research Council of Canada, Ottawa, Ontario, K1A 0R6, Canada |
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| Abstract: | The hygroscopic behaviour of NaCl, (NH4)2SO4, Na2SO4 and NH4NO3 particles in the size range of 0.1–20 μm was studied by environmental scanning electron microscopy (ESEM). This technique allows the in-situ observation of individual aerosol particles while changing the temperature and/or relative humidity (RH) in the sample chamber. The hygroscopic behaviour of these particles (e.g., deliquescence, adsorption of water on the particle surface) becomes directly observable with a lateral resolution of the order of 8–15 nm. The deliquescence relative humidities (DRH) of the different salts, the temperature dependence of the DRH for NH4NO3, and the growth factors (at increasing relative humidities) for NaCl were determined. Generally, a good agreement between the values obtained by ESEM and those found in literature was achieved. However, the DRH of NaCl determined by ESEM is systematically higher (approximately 2%, absolute) than the values obtained by other techniques, which can be explained by the observed strong absorption of water onto the crystal surface prior to droplet formation. The efflorescence behaviour of individual particles can be studied only qualitatively due to influences of the sample substrate. Furthermore, it is demonstrated that the activation of soot can be studied at high resolution by ESEM. |
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| Keywords: | Environmental scanning electron microscopy Deliquescence Relative humidity Individual particle analysis Hygroscopy |
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