Characterization of individual aerosol particles in workroom air of aluminium smelter potrooms

Aerosol particles with aerodynamic diameters between 0.18 and 10 μm were collected in the workroom air of two aluminium smelter potrooms with different production processes (Søderberg and Prebake processes). Size, morphology and chemical composition of more than 2000 individual particles were determined by high resolution scanning electron microscopy and energy-dispersive X-ray microanalysis. Based on chemical composition and morphology, particles were classified into different groups. Particle groups with a relative abundance above 1% (by number) include aluminium oxides, cryolite, aluminium oxides–cryolite mixtures, soot, silicates and sea salt. In both production halls, mixtures of aluminium oxides and cryolite are the dominant particle group. Many particles have fluoride-containing surface coatings or show agglomerations of nanometer-sized fluoride-containing particles on their surface. The phase composition of approximately 100 particles was studied by transmission electron microscopy. According to selected area electron diffraction, sodium β-alumina (NaAl11O17) is the dominant aluminium oxide and cryolite (Na3AlF6) the only sodium aluminium fluoride present. Implications of our findings for assessment of adverse health effects are discussed.