Use of Cluster Analysis to Evaluate the Characteristics of Acid Precipitation in Northern Taiwan

• Main Authors: Lee, How-Ming, 李灝銘
• Other Authors: Chang M.B., Lin N.H.
• Format: Others
• Language: zh-TW
• Published: 1996
• Online Access: http://ndltd.ncl.edu.tw/handle/09641214527355272713

碩士 === 國立中央大學 === 環境工程學系 === 84 === Cluster analysis has been successfully used in many realms of science. It can classify data into groups with similar structure and/or character. The extent of acidity of rainwater in Taiwan, especially in northern Taiwan, is as serious as that in eastern American. One possible cause which has been speculated is trans-border pollutants from mainland China. Therefore, this study tries to apply cluster analysis to evaluate the characteristics of acid precipitation in Taipei, Kwaisan, Chungli and Lotung, using the data collected in these acid rain monitoring stations from January 1991 through November 1995. Moreover, this study hopes to set up an easier and impeccable procedure of cluster analysis.Preliminary results show that the potential sources of ion composition of acid precipitation can be classified into three classes: sea salt, local pollution and mixing source which is correlated with sulfate. The spatial characteristics show that acid precipitation in urban stations, i.e. Taipei, Kwaisan and Chungli, contains higher sulfate concentration than that in rural station (Lotung). How acid substance levels vary in response to changes in atmospheric conditions depends on the prevailing meteorological situations. Northeast monsoon and summer shower are well marked in the analysis. When northeast monsoon is prevailing, concentrations of sea-salts are relatively higher during this period in all four stations located in northern Taiwan compared with other periods, and the ratios of [SO42-] / [NO3-] are higher too. This phenomenon shows that a proportion of sulfate may be transported by northeast monsoon and form the acid precipitation in Northern Taiwan. When local shower is prevailing, concentrations of nitrate, during this period, are obviously higher compared with other periods, but the ratios of [SO42-] / [NO3-] are lower. This phenomenon shows that ion compositions of the rains mainly come from local pollution. One interesting feature of clustering results obtained is that rain events within some clusters also occur in the same periods (meteorological situation), although no information about time is used in the analysis. Good correlation between the meteorological situations and the chemical compositions of the rains enables us to better understand the phenomena of acid precipitation in northern Taiwan. That is, rain events happened during similar period own the similar precipitation characteristics, and this result shows that cluster analysis of acid precipitation data in northern Taiwan is practicable. Moreover, the limitations of cluster analysis and the ways to improve have been discussed in this study.