Phase separation and regrowth of aerosol matter collected after size fractionation in an impactor |
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| Authors: | K Wittmaack N Menzel H Wehnes U Heinzmann |
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| Institution: | 1. Institute of Radiation Protection, GSF-National Research Centre for Environment and Health, Neuherberg, 85758 Germany;2. Institute of Pathology, GSF-National Research Centre for Environment and Health, 85758 Neuherberg, Germany;1. School of Environmental and Rural Science, University of New England, Armidale, 2350, NSW, Australia;2. ETH Zürich, Department Umweltsystemwissenschaften, Zurich, Switzerland;1. State Key Laboratory of Coal Resources and Safe Mining & College of Geoscience and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China;2. School of Earth and Environmental Sciences, Cardiff University, Cardiff CF10 3YE, Wales, UK;3. School of Energy & Environment Engineering, Zhongyuan University of Technology, Zhengzhou 450007, Henan, China;4. School of Resources and Materials, Northeastern University at Qinhuangdao, Qinhuangdao, 066004, China;5. Faculty of Environmental and Symbiotic Sciences, Prefectural University of Kumamoto, Kumamoto 862-8502, Japan;6. Hebei Center for Ecological and Environmental Geology Research, Hebei GEO University, Shijiazhuang 050031, China;7. Institute of Earth Sciences, China University of Geosciences (Beijing), Beijing 100083, China;8. School of Forestry, Jiangxi Agricultural University, Nanchang 330045, China;9. Hebei University of Economics and Business, Shijiazhuang 050061, Hebei, China;10. School of Biosciences, Cardiff University, Cardiff CF10 3AX, Wales, UK;1. School of Economics and Management, China University of Geosciences, Beijing, 100083, China;2. Key Laboratory of Carrying Capacity Assessment for Resource and Environment, Ministry of Natural Resources of the People''s Republic of China, Beijing, 100083, China;1. Department of Dentistry, University of Ponta Grossa, Ponta Grossa, Paraná, Brazil;2. Egas Moniz Center for Interdisciplinary Research (CiiEM), Egas Moniz School of Health & Science, Caparica, Almada, Portugal;3. Department of Dental Medicine, Karolinska Institutet, and the Scandinavian Center for Orofacial Neurosciences (SCON), Flemingsberg, Huddinge, Sweden;4. Department of Dentistry, Ingá University Center, Uningá, Maringá, Paraná, Brazil;5. Department of Physics, University of Ponta Grossa, Ponta Grossa, Paraná, Brazil |
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| Abstract: | Aerosol matter in the size range <2 μm was collected in a Berner impactor and subsequently analysed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectrometry. Owing to the low electron beam energy of 5 keV (occasionally 10 keV), analysis was restricted to elements with atomic numbers 20 (Ca). Sub-micrometer aerosol matter was found to contain mostly S, O, and C as well as some K and Ca. Nitrogen appeared to escape detection, probably due to bombardment-induced sublimation of NO3 and NH4. During sampling at low to moderate relative humidity (<60%) the sulphur-rich fraction of the aerosol matter (most likely sulphates) regrew in the form of microcrystals with sizes up to 10 times larger than the mean aerodynamic diameter of the respective impactor stage. By contrast, when sampling during periods in course of which the relative humidity exceeded 70%, the aerosol matter regrew in the form of extended amorphous agglomerates. The aerosol deposits also contained large numbers of carbon nanoparticles, well separated from the regrown sulphate-rich matter. The nanoparticles were similar in size (20–40 nm), much smaller than the equivalent aerodynamic diameter of the impacting particles (63 nm–2 μm). Presumably, the carbon nanoparticles constituted the core of larger air-borne particles covered with sulphates (as well as with nitrates and organic carbon). The regrown microcrystals disappeared rapidly under electron bombardment at high current density, an observation that indicates high volatility at elevated temperatures. Aerosol matter collected in the size range between 1 and 2 μm contained large fractions of particles made of O, Si, P, K, and Ca (oxides). These particles were highly resistant to electron bombardment (hard) and showed little or no evidence for agglomeration or regrowth. After removing the soluble (acidic) material from the collected aerosol matter, only carbon nanoparticles and hard coarse particles were left behind. The observation of agglomerated or crystallized “soft” aerosol matter in combination with phase separation of carbon nanoparticles lends further support to the assertion that it is not possible to collect useful quantities of fine and ultrafine aerosol particles with as-suspended morphology. Some implications for health-related research are discussed. |
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| Keywords: | Scanning electron microscopy Atmospheric aerosols Regrowth Phase separation Microcrystals Carbon nanoparticles |
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