Mixing state of aerosol particles at Mt. Hotaka, Japan: A case study in winter

Individual aerosol particles collected by a two-stage impactor on Mt. Hotaka (2165 m altitude) in central Japan in winter are studied using a transmission electron microscope and an energy-dispersive X-ray (EDX) analyzer. The size, morphology, elemental composition, mixing state and relative abundances are examined for (~ 550 ) aerosol particles with sizes of 0.1–2.0 μm collected during winter monsoon. Further smaller fine-ultrafine (~ 920) particles with sizes of 0.02–0.5 μm are also studied by electron-beam bombardment. There are potassium-containing sulfur particles, which may be originated from biomass burning or biofuel combustion in the Asian continent; sulfur would accumulate on these particles during their transport. Mineral particles and soot-containing particles constitute the minor abundance (less than 10% of all the particles). The samples collected during snowfall contain a very high fraction (> 90%) of fine sulfur-rich particles and no coarse particles are collected; precipitation may scavenge these coarse particles from the atmosphere. The electron-beam bombardment analysis reveals that the most abundant particles are the electron-beam sensitive (damaged) particles, which account for 70–90% of the total particles. On the basis of the comparison of fine particles with the diameter ranges of 0.1–0.5 μm obtained by both the EDX analysis and electron-beam bombardment analysis, the electron-beam sensitivity/insensitive particles would correspond to sulfur-containing particles/soot or mineral particles although we cannot deny out other particles such as nitrate, organics.