Atmospheric iron deposition in a megacity of northwest China: Solubility, speciation, and deposition fluxes

Abstract

Atmospheric iron has crucial effects on biogeochemical cycles, atmospheric processing, global climate, and human health. In this study, atmospheric dustfall samples were collected from six functional areas in Xi'an, China, from 2020 to 2021. The spatiotemporal distributions and deposition fluxes of total and water-soluble (ws) Fe as well as the speciation and potential sources of ws-Fe were characterized. Industrial areas had the highest concentrations of total Fe and ws-Fe, which were mainly due to copious emissions of heavy metals during manufacturing. The total Fe concentrations peaked in spring, primarily due to the substantial input of crustal dust, which also led to the lowest Fe solubility in this season. By contrast, the highest levels of ws-Fe occurred during winter due to an increase in biomass combustion. Among the water-soluble forms, ws-Fe (II) was dominant and accounted for 74.8% of the total amount of ws-Fe. Crustal dust was the main contributor to total Fe, whereas biomass burning primarily contributed to peak ws-Fe concentrations. The average total and ws-Fe deposition fluxes in Xi'an were the highest in spring and lowest in autumn, which were related to the distributions of the dustfall deposition fluxes and their Fe contents during these periods. Our study provided a broader and comprehensive understanding of atmospheric iron deposition in Chinese urban area, which is of positive significance for understanding atmospheric chemistry and global climate change.