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

• Published in: Atmospheric chemistry and physics Vol. 19; no. 2; pp. 1195 - 1206
• Main Authors: Lin, Qinhao, Bi, Xinhui, Zhang, Guohua, Yang, Yuxiang, Peng, Long, Lian, Xiufeng, Fu, Yuzhen, Li, Mei, Chen, Duohong, Miller, Mark, Ou, Ji, Tang, Mingjin, Wang, Xinming, Peng, Ping'an, Sheng, Guoying, Zhou, Zhen
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 30-01-2019; Copernicus Publications
• Subjects: Aerosols; Atmospheric particulates; Bioavailability; Chlorides; Cloud droplets; Cloud formation; Clouds; Combustion; Counterflow; Dust; Dust particles; Dust storms; Iron; Mass spectrometry; Oxalic acid; Oxidation; Photolysis; Precursors; Residues; Species; Sulfates; Vanadium
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-19-1195-2019

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.