Morphological and chemical characteristics of Fe-bearing particles during dust and non-dust periods in spring (2023) in a northern coastal city

Abstract

Atmospheric iron (Fe)-bearing particles are crucial in human health and climate systems. In this study, we investigated the elemental concentrations and morphological characteristics of Fe-bearing particles during a non-dust period and two dust periods in the spring of 2023. Analyses were conducted using an energy-dispersive X-ray fluorescence spectrometry (XRF) and a scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX). The results showed that the mass concentrations of Fe in PM_2.5 were 0.74 μg m⁻³ during non-dust period and 8.17 μg m⁻³ during the dust periods, indicating a substantial contribution of dust storms to Fe transport toward downstream regions. Fe-bearing particles accounted for 65.6 % and 91.1 % (by number) of total analyzed non-carbonaceous particles during the non-dust and dust periods, respectively. Notably, the proportion of Fe-rich particles, likely composed of iron oxides, was higher in the non-dust period (8.6 %) compared to the dust periods (1.4 %). Individual particle analysis further revealed that Fe-bearing particles contained a higher sulfur (S) content during the non-dust period than the dust periods. Moreover, within the dust periods, the relative abundance of S-containing Fe-bearing particles increased in the later stages compared to the initial stages, suggesting progressive atmospheric aging. These findings highlight significant differences in the mineralogical composition and aging processes of Fe-bearing particles between dust and non-dust conditions, with implications for iron solubility and its subsequent effects on human health and climate feedbacks. This study underscores the necessity for further experimental investigations into iron dissolution under varying atmospheric conditions.