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. 2021 Sep:97:138-144.
doi: 10.1016/j.gr.2021.05.022. Epub 2021 Jun 2.

Variations in concentration and solubility of iron in atmospheric fine particles during the COVID-19 pandemic: An example from China

Lei Liu  1 , Qiuhan Lin  1 , Zhuoran Liang  2 , Rongguang Du  3   4 , Guizhen Zhang  5 , Yanhong Zhu  1 , Bing Qi  1 , Shengzhen Zhou  6 , Weijun Li  1
Affiliations

Variations in concentration and solubility of iron in atmospheric fine particles during the COVID-19 pandemic: An example from China

Lei Liu et al. Gondwana Res. 2021 Sep.

Abstract

Iron (Fe) in the atmosphere can affect atmospheric chemical processes and human health. When deposited into oceans, it can further influence phytoplankton growth. These roles of Fe fundamentally depend on its concentration and solubility. However, the sources of aerosol Fe and controlling factors of Fe solubility in megacities remain poorly understood. The outbreak of the COVID-19 pandemic causes large changes in human activities, which provides a unique opportunity to answer these key issues. Field observations were conducted before, during, and after the COVID-19 lockdown in Hangzhou, China. Our results show that in the COVID-19 lockdown stage, the concentrations of total Fe (FeT, 75.0 ng m-3) and soluble Fe (FeS, 5.1 ng m-3) in PM2.5 decreased by 78% and 62%, respectively, compared with those (FeT 344.7 ng m-3, FeS 13.5 ng m-3) in the pre-lockdown stage. The sharp reduction (81%) in on-road vehicles was most responsible for the aerosol Fe decrease. Surprisingly, the Fe solubility increased by a factor of 1.9, from 4.2% in the pre-lockdown stage to 7.8% in the COVID-19 lockdown stage. We found that the atmospheric oxidizing capacity was enhanced after lockdown restrictions were implemented, which promoted the formation of more acidic species and further enhanced the dissolution of aerosol Fe.

Keywords: Aerosol acidification; COVID-19; Enrichment factor; Iron solubility; PM2.5.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

None
Graphical abstract
Fig. 1
Fig. 1
Location of the observation site (NRCS) in Hangzhou. (Map copyright © Google Earth).
Fig. 2
Fig. 2
Time series of daily PM2.5, total Fe (FeT), and water-soluble Fe (FeS) concentrations and Fe solubility (%FeS) during the whole observation period in urban Hangzhou. The divisions of the pre-lockdown, COVID-19 lockdown, and post-lockdown stages are marked on the top of this figure.
Fig. 3
Fig. 3
Comparisons of (a) PM2.5, (b) total Fe (FeT), and (c) water-soluble Fe (FeS) concentrations and (d) Fe solubility (%FeS) among the pre-lockdown, COVID-19 lockdown, and post-lockdown stages. The box represents the 25th (lower line) and 75th (upper line) percentiles; the solid line and circle in the box represent the median and mean values, respectively; and the lower and upper whiskers represent the 10th and 90th percentiles, respectively.
Fig. 4
Fig. 4
Correlations between the Fe solubility (%FeS) and the molar ratio of (2SO42−+NO3−)/total Fe (FeT), colored by O3 concentration. The black line represents the linear regression for all the samples collected during pre-lockdown (solid squares), COVID-19 lockdown (solid circles), and post-lockdown (solid triangles) stages.
Fig. 5
Fig. 5
A conceptual model illustrating the changes in concentrations and sources of aerosol Fe after the implementation of COVID-19 lockdown in Hangzhou and the corresponding enhanced oxidizing capacity that increases the Fe solubility.
See this image and copyright information in PMC

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