Hygroscopic and chemical properties of aerosol emissions at a major mining facility in Iran: Implications for respiratory deposition

This study characterizes the hygroscopic and chemical nature of aerosols originating from ten locations (4 outdoors and 6 indoors) around the Gol-E-Gohar (GEG) iron ore mine (Iran), including an assessment of how hygroscopic growth alters particulate deposition in the respiratory system. Aerosols collected on filters in three diameter (D_p) ranges (total suspended particulates [TSP], D_p ≤ 10 μm [PM₁₀], and D_p ≤ 2.5 μm [PM_2.5]) were analyzed for chemical and hygroscopic characteristics. The water-soluble aerosol composition is dominated by species associated with directly emitted crustal matter such as chloride, sodium, calcium, and sulfate. There was minimal contribution from organic acids and other secondarily formed species such as inorganic salts. Aerosol growth factors at 90% relative humidity varied between 1.39 and 1.72 and exceed values reported for copper mines in the United States where similar data are available. Values of the hygroscopicity parameter kappa (0.19–0.45) were best related to the mass fraction of chloride among all the studied species. Kappa values were generally similar when comparing the three types of samples (TSP, PM_2.5, PM₁₀) at each site and also when comparing each of the ten sampling sites. Accounting for hygroscopic growth yields an increase in the deposition fraction for aerosols with a dry D_p between 0.2 and 2 μm based on International Commission on Radiological Protection model calculations, with more variability when examining each of the three individual head airway regions.