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

Lei Liu; Qiuhan Lin; Zhuoran Liang; Rongguang Du; Guizhen Zhang; Yanhong Zhu; Bing Qi; Shengzhen Zhou; Weijun Li

doi:10.1016/j.gr.2021.05.022

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

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

Authors

Lei Liu¹, Qiuhan Lin¹, Zhuoran Liang², Rongguang Du^{3

4}, Guizhen Zhang⁵, Yanhong Zhu¹, Bing Qi¹, Shengzhen Zhou⁶, Weijun Li¹

Affiliations

¹ Department of Atmospheric Sciences, School of Earth Sciences, Zhejiang University, Hangzhou 310027, China.
² Key Laboratory of Cities' Mitigation and Adaptation to Climate Change in Shanghai (CMACC), Shanghai 200092, China.
³ Hangzhou Meteorological Bureau, Hangzhou 310051, China.
⁴ Key Laboratory of Atmospheric Chemistry, China Meteorological Administration, Beijing 100081, China.
⁵ Jiande Meteorological Bureau, Jiande 311600, China.
⁶ School of Atmospheric Sciences and Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, Sun Yat-sen University, Guangzhou 510275, China.

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 (Fe_T, 75.0 ng m^-3) and soluble Fe (Fe_S, 5.1 ng m^-3) in PM_2.5 decreased by 78% and 62%, respectively, compared with those (Fe_T 344.7 ng m^-3, Fe_S 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.