Diurnal and seasonal variations of the tropospheric ozone in Indonesia

Abstract

Since December 1986, tropospheric ozone near the ground surface has been observed at Watukosek (7°35'S, 112°40'E), a village in East Java, with Dasibi ozone monitor. The observation site is located at a height of 50 meters above sea level, surrounded by agricultural areas with no roads for heavy traffic. From the analyzed ozone data for December 1986-March 1989 along with meteorological data, ozone concentration observed at Watukosek exhibits a significant diurnal variation. The feature of the diurnal variation is different from those in the middle geographical latitude. Ozone concentration begins to increase just after sunrise, attains its maximum before noon, generally shows gradual decrease until sunset and remains almost constant after midnight. The diurnal maximum, average and minimum are 40 ppbv, 20 ppbv and 10 ppbv respectively. Systematic seasonal trend of diurnal maximum is not found in the December 1986-March 1989 data. However, the diurnal maximum occurs at 10 a.m. local time in dry season (June-September) and 11 a.m. to 12 noon local time in the wet season (December-March). The early diurnal maximum is thought to be closely related with the development of sea breezes which carry low ozone concentration. For a detailed surface ozone analysis, a simultaneous data set for NOx, CO, methane and nonmethane hydrocarbons together with ozone is needed. Vertical structure of ozone also needs to be observed.