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    請使用永久網址來引用或連結此文件: http://ir.lib.ncu.edu.tw/handle/987654321/73878


    題名: 春季大氣環流對東南亞氣膠傳輸之影響
    作者: 林正直;Lin, Cheng-Chih
    貢獻者: 大氣科學學系
    關鍵詞: 七海計畫;長程傳送;生質燃燒
    日期: 2017-08-29
    上傳時間: 2017-10-27 12:28:16 (UTC+8)
    出版者: 國立中央大學
    摘要: 本研究藉由分析行政院環保署空氣品質監測網觀測資料以及NCEP大氣環境場資料,配合近幾年國內外學者所合作研究東南亞地區空氣污染源的七海計畫實驗(7SEAS),探討七海計畫實驗期間春季東南亞地區的生質燃燒行為如何藉由不同的氣候條件導致氣膠長程傳送過程產生差異,以及對臺灣的影響。
    以氣候觀點而言,在3月東亞高壓出海會和向西伸展的西北太平洋高壓合併,3月的局部東西向環流因中南半島在925hPa形成一組織完整的輻合中心而增強,由於此條件而使得生質燃燒所排放的空氣污染物被舉升至自由大氣後立即往東向順(下)風處傳送。在2010年七海計畫東沙實驗(7-SEAS/Dongsha Experiment)期間所收集的觀測資料,包含了3-4月間空氣污染物的6個長程傳送事件,這些事件是經由分析位於臺灣南部的恆春空氣品質監測站資料來確認。這些事件的分析確實和中南半島活躍的燃燒時期有關聯。在這些事件中所產生的空氣污染物經由2-3天在大氣中的時空旅程後傳送至臺灣來。進一步將上述的6個事件做合成分析,結果顯示出在燃燒相位期間大氣邊界層的西南氣流合(匯)流和位於中南半島晴空無雲下一組織完整的輻合中心之熱低壓,導致一明顯的上升運動而形成局部東-西向環流的向上分支。由上述推論上升運動連同活躍生質燃燒所產生強熱浮力,將空氣污染物向上攜帶至較低的自由對流層,在此空層空氣污染物沿著850hPa以上高度的西風有效率地往下風處傳送。而空氣污染物是被由寒潮反氣旋的下沉運動而引起局部東西胞/環流的向下分支帶至地面。
    上述提到氣膠的傳輸需仰賴氣流傳送,而氣流型態則完全取決於大尺度環流條件。在7SEAS的實驗中除了在2010年東沙實驗中發現恆春站有明顯的空氣污染物掉落至地面現象外,這部分在2013年另一個實驗計畫7-SEAS/BASELInE中的Lidar現地觀測和模式模擬都得到驗證。本研究發現造成上述東南亞生質燃燒污染物經長程傳送到降落至地面現象的主要機制,是由於寒潮反氣旋前沿的沉降作用以及高層短波槽後的下沉運動。比對此兩現地觀測實驗春季東南亞生質燃燒氣膠傳輸對接受區(臺灣)空氣品質影響之差異,分析結果顯示如下:(一)2010(2013)年春季東南亞地區的生質燃燒行為所產生氣膠經長程傳送至臺灣事件多(少),導致2010(2013)年春季臺灣空氣品質較差(好);(二)由大尺度平均環流場與距平環流場分析顯示2010(2013)年春季環流場大陸東北高壓勢力較弱(強),東南亞地區距平環流場盛行南(北)風,導致2010(2013)年春季東南亞地區生質燃燒產生的空氣污染物舉升至自由對流層後,較(不)容易經大氣環流往東長程傳送至臺灣。未來將進一步分析近10年春季大氣環流與東南亞氣膠傳輸之間年際變化的關係。
    ;By using the pollutants concentrations observed by the Taiwan Air Quality Monitoring Network (TAQMN) from Taiwan Environmental Protection Administration (EPA) and both NCEP and ECWMF reanalysis data, this research effort especially investigated the influence of long-range transport of the Southeast Asian biomass burning aerosols on the downwind surface air quality, particularly in Taiwan, under different weather and climate regimes.
    Climatologically, the East Asian high merges with the westward expansion of the northwestern Pacific subtropical high in March. The local East-West cell/circulation is enhanced by a well-organized convergent center that forms over Indochina at 925 h Pa in March. This allows the emitted air pollutants from the biomass burning to be uplifted to the free troposphere and immediately transported downwind to the east. Using the data collected from the 2010 7-SEAS/Dongsha Experiment, six cases of long-range transport events involving air pollutants during March-April were identified at the Hengchun air quality monitoring station in southern Taiwan. These events were related to active burning phases over Indochina Peninsula. The air pollutants produced by these events were transported to Taiwan after a 2e3 day journey. A composite analysis for these identified six cases showed that the boundary layer of the southwesterly flow confluence coupled with a well-organized convergent center located over a thermal low under clear skies over the Indochina Peninsula may induce a distinct ascending motion to form the upward branch of the transient local East-West cell/circulation during the burning phase. This inferred upward motion together with the strong thermal buoyancy created by the active biomass burnings could carry the air pollutants to the lower free troposphere where they would effectively be conveyed downwind along the westerly flow above 850 h Pa level. The air pollutants were brought down to the surface by downward branch of the transient local East-West cell/circulation, which was induced by the subsidence of a cold surge anticyclone. Using continuous point sources, the six identified cases were simulated with the Hybrid Single-Particle Lagrangian-Integrated Trajectory (HYSPLIT) particle dispersion forward model to confirm our supposition regarding the mechanism for the long-range transport of Southeast Asian biomass burning pollutants that has a significant impact on the surface air quality of the downstream areas, particularly in Taiwan.
    The transport of aerosols highly relies upon the air flow to convey, however, the air flow pattern is completely dominated by the large-scale circulation condition. One of the missions for the 2013 7-SEAS/BASELInE (Seven SouthEast Asian Studies/Biomass-burning Aerosols & Stratocumulus Environment: Lifecycles and Interactions Experiment) campaign was to capture/confirm the downwind effect on the surface air quality due to the long-range transport of Southeast Asia biomass burning (SEA BB) pollutants that was first discovered during 2010 Dongsha experiment. Fortunately, this phenomena was directly observed by Lidar system at Hengchun in southern Taiwan. The most significant findings in this study is the upper level ridge-trough short wave within 20°-35°N was very active during 2013 spring. Through the three dimensional structure analysis, it was also found that the sinking motion behind the upper level active short wave trough is the major mechanism to help enhancing the subsidence of cold surge leading edge. In turn, the enhanced subsidence of cold surge leading edge might bring down the long-range transport of the SEA BB pollutants to the surface. Furthermore, the HYSPLIT backward air trajectories model was performed to help identifying the SEA BB pollutants in the mid-troposphere while the fine resolution WRF model simulation was employed to demonstrate the detailed time evolution of the brought-down aerosols process in coping with the evidence from particle depolarization Lidar observation. For the future study, we will further investigate the inter-annual variation between the atmospheric circulation and long range transport of aerosol over Southeast Asia in recent decade during springtime.
    顯示於類別:[大氣物理研究所 ] 博碩士論文

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