Abstract
On the mountain side of Mt. Oyama, fog is frequently formed and pH of fogwater is low due to nitric acid formed from NOx. Recently, the concentration of fog components has increased because of a decrease in liquid water content (LWC) , which may be caused by a decrease of SPM as the condensation nuclei. The concentration of fog components becomes high when LWC is low, and acid fog events with fog water pH lower than 3.5 occur for about 20 % of fog duration at the mountainside (680 m a.s.l.) every year. It has been observed that the throughfall amount increased with an increase in altitude, although the precipitation amount does not depend on the altitude. It is caused by the fog deposition, which may be dominated by the fog formation frequency and the deposition rate of fog droplets depending on the wind velocity. The deposition of air pollutants on the canopies is caused by many path ways, rain, fog, gas, and aerosol. Deposited hydrogen ion is exchanged with metal ions in the leaves, and the application of simulated acid fog to the seedlings of fir, cedar, and beech in an experimental chamber showed that the amount of base cations leaching from leaves increased with decreasing pH of the applied acid fog solutions. Fir and beech seedlings were severely damaged by the long term application of simulated acid fog. Acid depositions on the surface soil is large in Mt. Oyama, and the soil has been acidified for recent years.
