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

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 Soderberg 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) cm(2) 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.