Pollen decreases with increase in yellow sand from continent: study.
Environmental scientists said Saturday the amount of pollen dispersed in Japan is inversely proportional to that of yellow sand blown from China and Mongolia.
Researchers at the Yamanashi Institute of Environmental Science in Kofu said they found that the amount of yellow sand and pollen changes on a roughly 10-year cycle.
Satoshi Koshimizu, the institute's research department head who led the team, said the cycle resembles that of the sunspot cycle but the causal relationship between the two cycles has yet to be explored.
Koshimizu will report the findings at a conference on Earth and planetary sciences to be held in Chiba beginning Sunday.
The Koshimizu group deduced the amount of yellow sand in the past 100 years by calculating the quantity of silica, a constituent of yellow sand, in the sediment at the bottom of Kawaguchi Lake in Yamanashi and compared it with the amount of cedar and Japanese cypress pollen detected over the past 30 years in Kofu.
According to the study, yellow sand blew into Yamanashi on nine days in 1990 and the average cedar and cypress pollen count was 3,000 per square centimeter in Kofu that year.
No yellow sand blew into the city in 1995 and the pollen count was 20,000 per square centimeter.