| dc.description.abstract | Lanyu is the only remote island of Taiwan with long-term measurements of background atmospheric SO2 and O3. The observation started from March, 1995 until present. Due to the improvement of modern sulfur removal process and strict emission regulations, the concentration of SO2 as a representative of the primary air pollutants has declined in recent years. However, the concentration of O3 as a secondary air pollutant was rising during the same period. This study investigates the long-term variations of SO2 and O3 at the Lanyu CWB station (22.04°N, 121.55°E, 324 m a.s.l.) to understand their characteristics in the western Pacific troposphere.
Our analysis shows that SO2 and O3 showed a decreasing trend with growth rates of -0.06 ± 0.03 ppb/yr and -0.36 ± 0.07 ppb/yr, respectively. In addition, we found a significant decline in O3 with a monthly concentration of 9.5 ppb because of strong southwesterlies in July, 2017. Based on the cluster analysis of HYSPLIT backward trajectories with 5 groups suggested: (1) China, (2) Japan, (3) The Pacific Ocean, (4) South China Sea, and (5) Local, the change of air mass origins was responding for the distinct seasonal O3 variations. Elevated O3 concentrations were mainly corresponding to north/northeast winds, whereas reduced O3 concentrations were mainly corresponding to south/southwest winds. However, no significant SO2 difference was found between the 5 groups. The influences of tourists were suggested responding for the seasonal and diurnal variations of SO2 as a result of emissions by the fire power plant lies to the southwest of the Lanyu station. For instance, more electricity demands during the peak period (April - September) and during the daytime (7:00 – 16:00 local time).
In this study, two typical pollution events were also investigated: (1) Long-range transport of Chinese air pollutants was mainly driven by northeastertlies. (2) Air pollution spread from Taiwan Main Island occurring with southwesterlies. MERRA-2 data were used for analyzing the characteristics of the two types of high concentration events. | en_US |