The presence of iron in the atmosphere has significant implications for global nutrient delivery, human health, and several chemical cycles. Globally, the primary source of iron in the atmosphere is wind-blown dust from arid environments. However, in urban areas, iron is also produced via various combustion processes such as power generation and vehicle exhaust.
Salazar et al.  present field data from the Platte River Air Pollution and Photochemistry Experiment (PRAPPE). They compare atmospheric particulate matter samples collected during the summer and winter at an urban, agricultural, and a mixed site on the Eastern Colorado plains. As metallic iron has not been found in atmospheric dust, the pervading presence of metallic iron across all their sites (although concentrated in the rural site) raises intriguing new questions about the origin of iron in the atmosphere. Also, the previously unobserved presence of atmospheric iron found in conjunction with organic matter introduces the possibility that combustion-derived iron is more prevalent than scientists had initially considered.
Citation: Salazar, J. R., Pfotenhauer, D. J., Leresche, F., Rosario‐Ortiz, F. L., Hannigan, M. P., Fakra, S. C., & Majestic, B. J. . Iron speciation in PM2.5 from urban, agriculture, and mixed environments in Colorado, USA. Earth and Space Science, 7, e2020EA001262. https://doi.org/10.1029/2020EA001262
—Jonathan H. Jiang, Editor, Earth and Space Science