In-cloud formation of secondary species in iron-containing particles

Abstract

Abstract. The increase in secondary species through cloud processing potentially increases aerosol iron (Fe) bioavailability. In this study, a ground-based counterflow virtual impactor coupled with a real-time single-particle aerosol mass spectrometer was used to characterize the formation of secondary species in Fe-containing cloud residues (dried cloud droplets) at a mountain site in southern China for nearly 1 month during the autumn of 2016. Fe-rich, Fe-dust, Fe-elemental carbon (Fe-EC), and Fe-vanadium (Fe-V) cloud residual types were obtained in this study. The Fe-rich particles, related to combustion sources, contributed 84 % (by number) to the Fe-containing cloud residues, and the Fe-dust particles represented 12 %. The remaining 4 % consisted of the Fe-EC and Fe-V particles. It was found that above 90 % (by number) of Fe-containing particles had already contained sulfate before cloud events, leading to no distinct change in number fraction (NF) of sulfate during cloud events. Cloud processing contributed to the enhanced NFs of nitrate, chloride, and oxalate in the Fe-containing cloud residues. However, the in-cloud formation of nitrate and chloride in the Fe-rich type was less obvious relative to the Fe-dust type. The increased NF of oxalate in the Fe-rich cloud residues was produced via aqueous oxidation of oxalate precursors (e.g., glyoxylate). Moreover, Fe-driven Fenton reactions likely increase the formation rate of aqueous-phase OH, improving the conversion of the precursors to oxalate in the Fe-rich cloud residues. During daytime, the decreased NF of oxalate in the Fe-rich cloud residues was supposed to be due to the photolysis of Fe-oxalate complexes. This work emphasizes the role of combustion Fe sources in participating in cloud processing and has important implications for evaluating Fe bioavailability from combustion sources during cloud processing.

High Production of Soluble Iron Promoted by Aerosol Acidification in Fog

“…One possible reason is that SO 4 2− and NO 3 − are the predominant salts produced in the polluted urban air at Qingdao. Another possible reason is that only some Fe‐rich particles may contain oxalate (Lin et al, 2019). Because simulated pH was not available for all samples due to the limit of the model (Text S2), we used SO 4 2− and NO 3 − to represent the aerosol acidity.…”

Field Evidence of Fe-Mediated Photochemical Degradation of Oxalate and Subsequent Sulfate Formation Observed by Single Particle Mass Spectrometry

“…24−26 Recent single particle studies have emphasized the possibility of WSOC formation in oxalate−-Fe particles, but have also noticed a daytime decrease of these oxalate−Fe particles. 27,28 All these studies highlight the importance of ferrioxalate photochemistry in the transformation of organics in atmospheric aqueous phases.…”

Iron solubility in fine particles associated with secondary acidic aerosols in east China

“…Therefore, it is important to understand %Fe S in continental air polluted by various anthropogenic sources. Chemical processing of aerosols during transport and aging in the atmosphere has been hypothesized to influence %Fe S (Shi et al, 2011;Ito, 2015;Shi et al, 2015;Lin et al, 2019;Xie et al, 2020). Aerosol acidification involving anthropogenic pollutants was thought to be an important hypothesis: acids produced from anthropogenic pollutants can dissolve aerosol Fe, thus increasing %Fe S (Meskhidze et al, 2003;Rubasinghege et al, 2010;Zhang et al, 2018).…”