Sources and processes of iron aerosols in a megacity in Eastern China

Yanhong Zhu,Pingqing Fu,Jinhui Shi,Longyi Shao,Lei Liu,Liang Xu,Yue Wang,Weijun Li,Daizhou Zhang,Jian Zhang,Jingsha Xu,Zongbo Shi

doi:10.5194/acp-22-2191-2022

Abstract

Abstract. Iron (Fe) in aerosol particles is a major external source of micronutrients for marine ecosystems and poses a potential threat to human health. To understand the impacts of aerosol Fe, it is essential to quantify the sources of dissolved Fe and total Fe. In this study, we applied receptor modeling for the first time to apportion the sources of dissolved Fe and total Fe in fine particles collected under five different weather conditions in the Hangzhou megacity of Eastern China, which is upwind of the East Asian outflow. Results showed that Fe solubility (dissolved Fe to total Fe) was the largest on fog days (6.7 ± 3.0 %), followed by haze (4.8 ± 1.9 %), dust (2.1 ± 0.7 %), clear (1.9 ± 1.0 %), and rain (0.9 ± 0.5 %) days. Positive matrix factorization (PMF) analysis suggested that industrial emissions were the largest contributor to dissolved Fe (44.5 %–72.4 %) and total Fe (39.1 %–55.0 %, except for dust days) during haze, fog, dust, and clear days. Transmission electron microscopy analysis of individual particles showed that > 75 % of Fe-containing particles were internally mixed with acidic secondary aerosol species on haze, fog, dust, and clear days. Furthermore, Fe solubility showed significant positive correlations with aerosol acidity/total Fe and liquid water content. These results indicated that the wet surface of aerosol particles promotes heterogeneous reactions between acidic species and Fe aerosols, contributing to a high Fe solubility.

Highlights

The deposition of atmospheric aerosols is a major external source of iron (Fe) in the ocean (Li et al, 2017; PinedoGonzález et al, 2020; Yang et al, 2020)
About 100 %, 29 %, and 8 % of PM2.5 concentrations on haze, fog, and dust days were higher than the grade II national PM2.5 standard of 75 μg m−3 (24 h average standard; GuoBiao (GB) 3095-2012, China), respectively
Total Fe concentrations differed significantly according to the weather conditions (p < 0.01 or 0.05; independent sample T test; Table S4), except between haze and clear days (p > 0.1) and between fog and clear days (p > 0.5)

Summary

Introduction

The deposition of atmospheric aerosols is a major external source of iron (Fe) in the ocean (Li et al, 2017; PinedoGonzález et al, 2020; Yang et al, 2020). Schroth et al (2009) suggested that Fe solubility was less than 1 % of the iron in arid soils, while oil combustion emissions had a pronounced effect on Fe solubility (77 %–81 %); Oakes et al (2012) studied Fe solubility in anthropogenic source emission samples and found that Fe solubility was 0.06 % in coal fly, 46 % in biomass burning, 51 % in diesel exhaust, and 75 % in gasoline exhaust. These results imply that an increase in relative amounts of aerosols from these mixed anthropogenic sources may be responsible for the increase in Fe solubility

Methods

Results

Conclusion