雲嘉南地區高臭氧污染時空變異與污染來源分析探討

Abstract

近年來在雲嘉南地區的臭氧污染有逐年惡化的趨勢，因此本研究以多變量統計方法及光化學軌跡模式分析近年來空氣品質監測資料，深入瞭解各重大污染源對於雲嘉南地區臭氧污染的貢獻，提供臭氧管制策略之參考依據。 本研究首先探討雲嘉南地區臭氧汙染的時空變異情形，結果顯示2003∼2005年雲嘉南地區秋季臭氧超標百分比高達57％，而台南地區因為季節風向的關係，使得秋季的臭氧超標情形較為嚴重。進而利用前5％的成分分數篩選出有代表性的臭氧事件日，因為秋季雲嘉南地區暴露在長時間低臭氧濃度下較嚴重，與非事件日的比較中得知若是處於氣象條件不利擴散的情況，就容易出現臭氧的尖峰值，在軌跡線通過汙染源的情況下，除非擴散條件良好否則就會造成高臭氧的生成，因此必須管制臭氧前驅物才能有效的削減臭氧的增量。 集群分析將雲嘉南臭氧地域分類成四個族群，利用逆軌跡分析瞭解造成各族群臭氧汙染的主因。第一類地區因為沒有大量NOX所以臭氧汙染較不嚴重；第二類地區累積了大量的VOC與NOX，因此生成高臭氧的污染；第三類地區經過工業區的比例不高，部分的臭氧是從北邊傳輸而來；第四類地區的污染來源較為廣泛，發生臭氧高濃度時間較晚。而整體雲嘉南地區臭氧污染來源通過工業區的比例高達48％，所以在雲嘉南地區VOC是主要造成高臭氧的主因，若處於氣象條件不利擴散的情況下氣團就會吸納較多的VOC，與下風處的NOX反應造成臭氧小時值超標的現象，如果能有效的管制VOC的排放量，那麼生成高臭氧的機會就會降低許多。

In these years, the pollution of ozone becomes worse in Yunlin-Chiayi-Tainan (Y-C-T) area in Taiwan. This study used multivariate statistical analysis and trajectory photochemical air quality model to analyze the database of air quality monitoring station. The goal of this study was to understand the pollution magnitude produced by sources of pollution, and provided the basis for control of ozone. This study investigated that the change on spatial and temporal variations of (Y-C-T) area. The results indicated that the percentage of over-standard of ozone was 57% in 2003 to 2005, and the ozone pollution was worse in Tainan in fall due to the direction of the wind. The study used top 5% of component scores to choose the representative ozone episodes. Compare with non-ozone episodes, the results indicated that the highest concentration of ozone was produced by sources of pollution when the climate was not conductive to diffuse. For decrease the magnitude of ozone, ozone precursors should be controlled. This study used cluster analysis to classify (Y-C-T) area to be four regions, and used analysis of backward trajectory to understand the main reason of ozone pollution in each cluster. The result indicated that the pollution of ozone was fine with less NOx in first region. And the serious ozone population was occurred in the second region due to accumulation of VOC and NOx. In the third region, there was low percentage of the trajectory lines across the region of industry, and some of ozone came from north of the cluster. There were widespread sources of ozone pollution in the fourth region, and the occurred time of high concentration of ozone is later than the other regions. Overall, the percentage of the trajectory lines across the regions of industry was 48%, so the VOC was the main reason to produce high concentration of ozone in (Y-C-T) area. When the climate was not conductive to diffuse, the air mass sucked in more VOC and caused high concentration of ozone. Therefore, the emission of VOC should be controlled in order to prevent the occurrence of high concentration of ozone.