Concentrations of SO2, NOx and O3 and their diurnal variation at Mt. Gokurakuji and its vicinity, Hiroshima prefecture, western Japan

Measurements of sulfur dioxide (SO2), nitrogen oxides (NOx), ozone (O-3), and meteorological parameters like wind speeds and wind directions were carried out from February 1997 to February 1998 at 4 sites of Mt. Gokurakuji (the elevation at the summit: 693 m), Hiroshima prefecture, in order to investigate the distribution patterns and diurnal variations of air pollutants with respect to areas of the Japanese red pine forest declines. SO2 concentrations were low (less than 10 ppb) at every observation site. Higher concentrations of NOx (80-330 ppb) were observed during the night time and early morning at the sites (altitude 120 m, 130 m) near the city area. NOx 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 O-3 at the summit was lower during north wind and increased during see breeze, which suggests that photochemically produced O-3 was transported from the city area in which NOx was emitted. Emission rates of NOx 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 NOx at the surrounding cities have been increasing slightly from 1985 and O-x concentrations have also been increasing every year. On the other hand, SO2 concentrations have been decreasing with the decrease of emission rates of SOx at the surrounding cities.