Sources and processes of iron aerosols in a megacity in Eastern China

Iron (Fe) in aerosol particles is a major external source of micronutrients for marine ecosystems and poses a potential threat to human health. To understand the impacts of aerosol Fe, it is essential to quantify the sources of dissolved Fe and total Fe. In this study, we applied receptor modeling for the first time to apportion the sources of dissolved Fe and total Fe in fine particles collected under five different weather conditions in the Hangzhou megacity of Eastern China, which is upwind of the East Asian outflow. Results showed that Fe solubility (dissolved Fe to total Fe) was the largest on fog days (6.7 ± 3.0 %), followed by haze (4.8 ± 1.9 %), dust (2.1 ± 0.7 %), clear (1.9 ± 1.0 %), and rain (0.9 ± 0.5 %) days. Positive matrix factorization (PMF) analysis suggested that industrial emissions were the largest contributor to dissolved Fe (44.5 %–72.4 %) and total Fe (39.1 %–55.0 %, except for dust days) during haze, fog, dust, and clear days. Transmission electron microscopy analysis of individual particles showed that > 75 % of Fe-containing particles were internally mixed with acidic secondary aerosol species on haze, fog, dust, and clear days. Furthermore, Fe solubility showed significant positive correlations with aerosol acidity/total Fe and liquid water content. These results indicated that the wet surface of aerosol particles promotes heterogeneous reactions between acidic species and Fe aerosols, contributing to a high Fe solubility