Forest decline has been found in the Tanzawa Mountains and O 3 is thought to be one of its causes. However, a three-dimensional analysis using numerical models has not been carried out in the Tanzawa Mountains. In this study, we carried out a study to understand the behavior of the O 3 concentration in the Tanzawa Mountains using numerical models (the meteorological and air quality models). The surface O 3 concentration in the mountains and its surrounding area did not depend on the model grid

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... ize of 15km and 5km. The diurnal variation in the surface O 3 concentration in the Tanzawa Mountains is low, because the O 3 chemical production is lower and the dry deposition is not lower than that around the air quality monitoring station in the daytime, and the sea breeze with fresh air does not reach the Tanzawa Mountains in the evening. The vertical O 3 concentration increases with the elevation or is constant with the elevation in the ABL (Atmospheric Boundary Layer). The O 3 concentration above the ABL immediately decreases with the elevation and reaches a background concentration (50ppb). The numerical models are effective tools for the simulation of the O 3 concentration in the Tanzawa Mountains, because numerical models can possibility complement the lack of O 3 monitoring in the Tanzawa Mountains.