Long term trends of dry and wet deposition of air pollutants at declining forest site of Mt. Oyama in Japan during 1994–2019

Abstract Forest decline, which occurs in mountainous regions many countries, may result from the effects of acid fog, ozone, or deposition other pollutants. We observed wet air pollutants at different altitudes on Mt. Oyama, situated southwest Tokyo, for 1994 until 2019. During this period, domestic atmospheric environment was improved Japan. The average concentration around all sampling sites Oyama decreased by 63.01%, 32.08%, 8.80%, and 39.73% NH 3 , HCl, HNO SO 2 respectively. volume weighted mean (VWM) pH values showed an increasing trend bulk (+0.70% y -1 ), fog water (+2.58% throughfall (+2.60% ). Stemflow also increased (cedar, +1.17% ; fir, +0.82% although it included organic acids dissolved stem primarily had a low VWM value. overall value site, acidic still observed. Comparing between winter summer, significant increase occurred whereas no change winter. In sources are mainly mainland Japan, frequency low-pH annually. winter, affected transboundary pollution, occasionally occurred. Improvements control pollution will provide better conditions mountain ecology that free