Strong inorganic acid mists containing sulfuric acid (H2SO4) have been reported to correlate well with lung and laryngeal cancers in humans. Phosphate fertilizer manufacturing facilities are listed as one of the many occupational exposures to strong acid. To better protect workers from potential exposure, a field campaign was carried out to investigate aerosol characteristics at eight phosphate fertilizer facilities using a UW-cascade impactor for size information and ion chromatography for water soluble species. The results show that acid mists were dominantly in the coarse mode when high concentrations were identified. An aerosol thermodynamic model was established to estimate the aerosol acidity. In the high-relative-humidity environment, the aerosol can reach its equilibrium size within 0.014 s, which is shorter than the traveling time of an aerosol in the upper respiratory system. The results indicate that aerosols sampled in this study may deposit in the upper respiratory tract, which is consistent with epidemiological evidence of a correlation between inhalation of strong inorganic acid mists and laryngeal cancer. However, extensive epidemiological studies of phosphate industry workers have not shown an increased incidence of any type of cancer. (C) 2007 Elsevier Ltd. All rights reserved.