[A-AS22_1PO1] Atmospheric Chemistry

[AAS22-P03] Properties of Fe-containing particles and structure of mineral particles in the mountain, urban, and marine atmosphere

*Yusuke MIKI¹, Sayako UEDA², Kazuhiko MIURA¹, Hiroki KATO¹, Hiroshi FURUTANI³, Mitsuo UEMATSU³ (1.Tokyo University of Science, 2.Nagoya University, 3.University of Tokyo)

Keywords:aerosol, Fe, water-soluble materials, water-insoluble materials, long-range transportation

Atmospheric aerosol particles play an important role in global material cycles and global climate by acting as an agent which transports materials over long distances. Iron (Fe) is an essential element for marine phytoplankton growth especially in high nutrient and low chlorophyll (HNLC) area. Long-range transportation of atmospheric aerosols from the continent and subsequent deposition is an important process to supply Fe to the ocean. The dry and wet depositions of aerosol particles depend on the particle size and the mixing states with water-soluble materials. In order to study the properties of Fe-containing particles and modification of individual particles, we collected aerosol particles at the top of Mt. Fuji, at Kagurazaka, Tokyo, and on the ship over the mid-latitude western North Pacific Ocean during the KH-12-1 (EqPOS) Leg 2 cruise of the R/V Hakuho Maru. We collected aerosol particles with a low pressure impactor. Collected particles were analyzed using a transmission electron microscopy (TEM) with a water dialysis method and an energy-dispersive X-ray (EDX) analysis. We chose the samples which were collected in the long-range transportation events from the continent on the basis of 5-day backward air trajectory analysis, number size distribution of aerosols measured by an optical particle counter (OPC), and the results of the TEM-EDX analysis. Water-insoluble materials such as mineral dusts and industrial anthropogenic metals are main sources of Fe. This study focused on water-insoluble materials and performed the EDX analysis. In each sample, most of water-insoluble materials were internally mixed with water-soluble materials (internal mixed particles). The volume percent of the water-soluble materials in the mixed particles on a marine sample was higher than that of other samples, indicating that water-insoluble materials as well as Fe-containing particles were mixed with water-soluble materials during transportation.Structures of some mineral particles were verified using the focused-ion-beam (FIB) technique. Particles larger than 5 μm collected on the Ti-plate were sliced into 200 nm in thickness. We performed selected-area electron diffraction (SAED) on the cross section of the sliced particles. On the basis of the diffraction patterns and EDX results, structures of the mineral particles were verified. CaCl₂ was found on the surface of the particle and bounded on CaCO₃, suggesting that CO₃^2- was replaced by Cl^- (CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O). Fe was included in the particle. There is a possibility that changing insoluble CaCO₃ to soluble CaCl₂ changes the ability of cloud nuclei and/or ice nuclei and the solubility of Fe.