冬夏季長程傳送影響台灣海域背景臭氧之模擬探討

Simulation Comparison of Winter Continental Air Mass and Summer Maritime Air Mass on Background Ozone near Taiwan

柳中明(Chung-Ming Liu) ； 葉銘德(Ming-Te Yeh) ； 彭立新(Li-Zing Peng) ； 吳俊傑(Chun-Chieh Wu) ； 劉紹臣(Shaw C. Liu)

《大氣科學》 32卷1期 (2004/03) Pp. 1-22

摘要

經由分析設於蘭嶼島的台灣背景大氣監測站資料，柳等(1999)指出在所有監測氣體中，臭氧是最佳之辨認季節性氣團變動的大氣化學物資，在冬季大陸乾冷氣團主控期間，即反應亞洲中高緯度大陸地區高臭氧濃度現象，而在夏季海洋暖溼氣團主控期間，則反應太平低緯度海洋地區低臭氧濃度現象。本文選擇冬夏各一個案，採用數值模擬的方式，來確認蘭嶼島監測資料主要反應長程氣團傳送影響；並分別進行無污染排放與考慮污染排放的數值模擬，以定量探討上游自然與人為污染的貢獻。
結果顯示：夏季時台灣受到來自南方太平洋與南海海域乾淨的海洋性空氣影響，臭氧濃度維持在18ppbv上下，其中自然背景濃度約在14ppbv以下，但因途經菲律賓低污染源區，造成臭氧先趨物質增加與臭氧濃度增加約14~28%，僅為2~4ppbv。冬季時，源自於西伯利亞及蒙古地區的高層空氣，由西北向東南方向行進，出海後高度急遽下降，將高層高濃度臭氧帶到近地面，造成洋面上大範圍的高臭氧濃度。過程中，途經中國大陸高污染源區，氣流將臭氧前驅物傳送到洋面，促成臭氧生成增加，臭氧濃度在東亞大陸附近洋面維持在45ppbv上下。其中，自然背景臭氧約使蘭嶼附近海域維持40ppbv濃度臭氧，大陸污染貢獻則約為5ppbv，相當於增加12.5%。顯然，夏季紫外線輻射強且氣溫高，因此雖然菲律賓污染排放量不大，但大環境有利於臭氧生成且背景濃度低，所以人為污染促成台灣海域背景臭氧濃度增加的比例較冬季時為顯著，雖然絕對增量偏低。

關鍵字

背景大氣監測 ； 臭氧 ； 長程傳送 ； 數值模擬

並列摘要

Analysis of data collected at Lanyu Baseline Station suggests that the data quality was as good as those measured at WMO supported international baseline stations. Ozone can be selected as the best indicator for monitoring the seasonal change of continental and maritime air-mass at Lanyu. It reveals that night-time averaged surface ozone concentration reaches a maximum level between 36.4～48.5 ppbv in winter and a minimum level between 13.5～22.6 ppbv in summer during March 1995～October 2003. Wintertime Asian cold airmass and summertime Pacific warm airmass are responsible for the observed higher and lower levels of ozone, respectively.
In this paper, a winter and a summer cases are selected to track back the source origins of air masses reaching Lanyu and to quantify the upstream transport and anthropogenic effects on local ozone level. A 3-d regional chemical transport model is used in this study.
The results show that in summer, maritime air coming from the Pacific and South China Sea maintains the ozone level around Taiwan near 18ppbv, which includes the 14～28% increase of ozone level (about 2～4 ppbv) caused by ozone precursors released from Philippines, Indonesia, etc. In winter, upper level air above Siberia and Mongolia descends southeastward toward the western Pacific and maintains the ozone level around Taiwan near 45ppbv, which includes the 12.5% increase of level (about 5 ppbv) caused by ozone precursors released from mainland China. It is interesting to note that even though the absolute amount of anthropogenic emissions from Southeast Asia is not in a huge volume; their contributions to the ozone production in the maritime area can not be ignored.

並列關鍵字

Background Ozone level ； Long-rang transport ； Numerical simulation