Black Acidic Rime Ice in the Remote Island of Yakushima, a World Natural Heritage Area

In order to clarify the long-range transport of atmospheric pollutants in the East Asian regions, we have studied the components in rime ice on Yakushima Island, located in southwestern Japan near the China continent. The presence of a large number of particles has been found in the rime ice. Very small particles whose diameters are around 1 µm were identified as coal fly ash. The air mass at an altitude between 1500 m to 2000 m was probably long-range transported in association with a stable atmospheric layer in which the particles were efficiently scavenged by supercooled droplets. A back trajectory analysis also indicated the predominance of a north wind in the winter and in the other seasons as well. Such transport and deposition mechanisms may produce the greater pollutant deposition sometimes observed in mountain areas. Similar events may not be rare and could make an important contribution to the annual pollutants.