Concentrations of SO₂, NO_x and O₃ and their diurnal variation at Mt. Gokurakuji and its vicinity, Hiroshima Prefecture, Western Japan

Measurements of sulfur dioxide (SO₂), nitrogen oxides (NO_x), ozone (O₃), and meteorological parameters like wind speeds and directions, were carried out from February 1997 to February 1998 at four sites of Mt. Gokurakuji (the elevation at the summit: 693 m), Hiroshima prefecture, to study the distribution patterns and diurnal variations of air pollutants with respect to areas of the Japanese red pine forest declines. SO₂ concentrations were low (< 10 ppb) at every observation site. Higher concentrations of NO_x (80-330 ppb) were observed during the night time and early morning at the sites near the city area. NO_x concentration near the summit of Mt. Gokurakuji was as high as 20 ppb at daytime and a few ppb at the nighttime and showed the different patterns of diurnal variation from those at the sites near the city area. Concentration of O₃ at the summit was lower during north wind and increased during sea breeze, which suggests that photochemically produced O₃ was transported from the city area in which NO_x was emitted. Emission rate of NO_x and the number of vehicles at the surrounding cities of Mt. Gokurakuji have been increased by a factor of 2.5 and 2.0, respectively, from 1980 to 1996. Annual concentrations of NO_x at the surrounding cities have been increasing slightly from 1985 and O₃ concentrations have also been increasing every year. On the other hand, SO₂ concentrations have been decreasing with the decrease of emission rates of SO₂ at the surrounding cities.