Long-term trends of greenhouse gases in regional and background events observed during 1998–2004 at Yonagunijima located to the east of the Asian continent

We performed trend analyses using hourly data of CO, CO2, CH4, and O3 from 1998 to 2004 on Yonagunijima (24°28′N, 123°01′E), which is a small island in south Japan and located close to the Asian continent. The hourly CO concentrations observed were classified as “regional events” or “background events” based on the time scale of the variations. In addition, the hourly mean CO2, CH4, and O3 concentrations observed were also classified as regional or background events based on the CO events. The trends in the regional and background events in the four parameters were analyzed separately. The annual mean CO concentration in the regional event classified above on Yonagunijima was well consistent with the annual coal consumption in China. The annual mean concentrations of all parameters in the regional event were higher than those in the background event. For CO and CO2, the mean growth rates classified as regional events were evidently larger than those classified as background events, and their concentration differences (concentration in the regional event minus that in the background event) have been increasing on Yonagunijima. As the frequency of regional events on Yonagunijima was 44%, the influence of the increase in regional events on the atmospheric environment in East Asia cannot be neglected.