Hygroscopic properties of the workroom aerosol in aluminium smelter potrooms: a case for transport of HF and SO2 into the lower airways

Abstract

The hygroscopic behaviour of individual aerosol particles from workplaces in a primary aluminium smelter was investigated by environmental scanning electron microscopy. At a high relative humidity, comparable with the human respiratory tract, most particles encountered in the Søderberg and Prebake potrooms either undergo partial deliquescence (leading to a water droplet with an insoluble core) or form thin water films at the surface. As gaseous HF and SO₂ are highly soluble in water, the aerosol particles may act as carrier for these two gases into the alveolar region of the lower respiratory tract. Based on a one-dimensional mass balance model, it is estimated that under peak exposure conditions (particle surface area concentration of 10⁻⁴ cm² cm⁻³) approximately 10% of the initial gaseous HF may be transferred to the particle phase. For SO₂, this fraction is much lower (approximately 1%). These results indicate that at least HF may penetrate deeper into the lung in the presence of soluble particles or particles that form surface water films compared to HF alone.