Variation of concentration of ozone in summer and autumn in Oku-Nikko mountainous area

Photochemical ozone transported from Tokyo metropolitan area is pointed out to be one of the important causes for the forest decline observed in the Oku-Nikko mountainous area. Therefore, it is necessary to monitor ozone in the mountains of Oku-Nikko. However, long term observation of ozone in the Oku-Nikko area has been quite limited due to lack of electric power supply. In the work reported here we set up an ozone monitor near the top of Mt. Mae-Shirane in Oku-Nikko. Twenty Ni-Cd batteries were set for electric power supply, and 20 solar panels were also set to charge those Ni-Cd batteries during day time. On the basis of three months observation of ozone we could analyze the long term variation of ozone there. The highest concentration in summer was -70 ppb. High concentrations of ozone were recorded in the evening in summer when polluted air mass was transported from the Kanto Plane. High concentration of ozone appeared when the south wind prevailed and solar radiation was strong. On the other hand, in autumn, ozone was very constant around 40 ppb. No significant diurnal variation was observed. The influence of free troposphere was suggested in autumn. The air mass came from the west after passing over the Sea of Japan. It is indicated that the air mass containing Asian background ozone had reached this area in that season. (author abst.)