Abstract Iron (Fe), especially soluble Fe, is critical in atmospheric fine particulate matter (PM) (PM2.5), while its source contribution remains unclear. Here, we systematically study soluble Fe from various sources through real‐world measurement, laboratory analyses, emission inventory, and model simulation. The water solubility of Fe in PM2.5 from incomplete combustion sources (i.e., residential solid fuel burning and on‐road vehicle exhaust) was 19.6–1,063.7 times higher than that from industrial sectors, brake wear, and natural dust. In contrast, PM2.5 from industrial plumes after wet flue gas desulfurization devices exhibited a pH lower than 3, elevating Fe solubility by 11.0–18.6 times via proton‐promoted dissolution. Among all sources, residential combustion and the steel industry were the predominant anthropogenic sources of soluble Fe emissions, with high emission intensity of 70.1 ± 26.5% and 78.8 ± 13.2% in Eastern and Southwestern China, respectively. Our findings highlight the critical roles of incomplete combustion and plume acidity in contributing Fe solubility, providing fundamental data for atmospheric Fe chemistry and ocean primary productivity.
Observations from the Little Bunker
Last updated: November 30, 2025 04:25 AM
Atmospheric CO₂
426.8 ppm
+18.1
ppm/year
Atmospheric CH₄
1927.61 ppb
+2.73
ppb/year
Global Temperature
+1.48 °C
Peak: +1.73°C
World Population
8.1 billion
+67
million/year