Critical insights on the chemistry and toxicity of fine particles from power and steel plant emissions in China

Airborne particulate matter (PM) pollution has long been a major threat to human health worldwide, often ignored, but now coming into focus. Specifically in China, two atmosphere-polluting industrial sectors, coal-fired power plants (CFPPs) and iron-steel plants (ISPs), were taken as examples to decipher and estimate the emission of key toxic components of fine particles (FPs; < 1 μm). In vitro tests revealed ISP-emitted FPs induced 12.4 times higher oxidative stress and 4.4 times higher cytotoxicity on human bronchial epithelial cells than CFPP-emitted FPs. Single-particle ICP time-of-flight MS analysis showed that 60 ± 4 % of the CFPP-emitted metal(loid)-containing FPs were multi-metal(loid)s FPs (mmFPs), mostly Si-rich mmFPs (∼80 %). In contrast, Fe-rich mmFPs dominated the ISP-emitted mmFPs, with their number concentrations 8.5 - 35.6 times higher than those from CFPPs. Random forest model and SHapley Additive exPlanation analysis identified Fe-rich mmFPs (especially Fe-sole fingerprinted FPs) as the top regulator of intracellular oxidative stress, while toxic metal(loid)s associated with Fe-rich mmFPs controlled cytotoxicity. Fe-rich FPs, including Fe-rich mmFPs and Fe-single-metal(loid) FPs, contributed over 30 % of the total toxic potency induced by FPs, exceeding any other chemical component. Based on the latest available emission data of PMs in 2019, Fe-rich FPs emitted from CFPPs and ISPs in China were estimated to be about 1.7 × 10²³ particles (ca. 5217 tons), annually. Among these emissions, ISPs contributed over 97 %, with sintering and ironmaking being the major contributors. Therefore, developing advanced filtration technologies and enhancing the monitoring of ISP emissions is strongly encouraged.