中尺度模式MM5與大氣擴散模式之整合應用：核廠污染擴散研究

An Integrated Application of MM5 Mesoscale Model and Air Dispersion Model: A Study of Pollutant Dispersion from Nuclear Power Plants

黃清勇(C.-Y. Huang) ； 莊博清(P.-C. Chuang)

《大氣科學》 30卷4期 (2002/12) Pp. 377-407

摘要

本文使用中尺度氣象模式(MM5)，先進行真實天氣系統之模擬，再將MM5模擬結果與空氣動力擴散模式進行整合應用，研究大型有限體積污染源之擴散過程。就氣象研究部分，本文探討冬季北台灣地區與大台北地區大氣邊界層及其環流特徵。依此局部環流變異之需求，設計兩個緊急擴散模擬區（大台北擴散區與台北核安區），模式水平解析度分別達1000公尺與333公尺。此高解析度模擬結果顯示，在東北季風下，北台灣邊界層明顯受環境風場及地形效應影響，在山勢較高處，晚上邊界層之高度較低，且其分布與地形高度變化頗為一致。但當上游風向轉為較具東風分量時，邊界層分佈明顯受地形環流擾動的影響，在台北盆地及大屯山下風處常伴有低値。在此真實天氣系統下假設一核能污染排放源，本文高解析度的擴散模擬顯示，大屯山區的污染物擴散現象呈現非常細微的局部地形環流效應。在冬季東北風的個案(96/12/01)，核一廠、核二廠的瞬間污染物大約在2小時後，即進入台北盆地到達西側，此時濃度大約是初始濃度的百分之一。若為連續排放源，核一廠在排放30分鐘後，濃度前緣已進入台北市，隨後並經南港、中山區一帶，但主要濃度仍偏於盆地西北側。在北風的個案(98/11/09)中，核二廠污染物經45分鐘可達東區（南港、松山區），而1小時後，由於大屯山背風渦旋回捲效應，到達西南區（古亭、永和）一帶。在東風個案中(98/11/13、99/01/26)，污染物的傳送現象幾乎都是繞流過大屯山區，大部分被盛行繞流带往桃園、中壢外海一帶。由於在盆地之背風渦旋與雪山山脈之下沉東風形成合流，產生阻卻作用，使偏東盛行風下繞行之污染物濃度不易侵入台北盆地。本文研究顯示中尺度MM5模式與空氣動力擴散模式結合使用，可對局部地區進行高解析度模擬，有助於複雜地形及複雜氣流下核能或一般空氣污染物擴散之評估與了解，並可供為即時作業預報需求用。

關鍵字

中尺度氣象模式MM5 ； 空氣動力擴散模式 ； 大氣邊界層

並列摘要

This study utilizes mesoscale numerical model MM5 to simulate real weather cases and then combine atmospheric dispersion model for study for finite-volume pollutant sources. This paper investigates the characteristics of circulation and pollutant dispersion with simulation focuses on northern Taiwan and metropolitan Taipei area with model resolutions of 1000m and 333m respectively. The high-resolution simulation results show very detailed planetary boundary layer (PBL) characteristics in relation to terrain effects under prevailing northeasterly wind. At higher elevation of the terrain, the PBL height in this area during the nighttime is lower and its variation primarily reflects the terrain height contour as the prevailing wind is nearly northeasterly. However, as the upstream environmental wind shifts to be more easterly, the PBL height is apparently modified by local terrain circulation with an extreme low value in the Taipei Basin and downwind of the Tar-Tun Mountain. The high-resolution dispersion simulation results indicate that the air pollutants from Nuclear Power Plants 1 and 2 enter Taipei and reach the western basin after 2h with the concentration reduced to one-hundredth in the case of prevailing northeasterly wind. The pollutants also contaminate Taipei City in the case of prevailing northerly wind but tend to have larger impact on its eastern part as well as the southwestern part later due to the recirculating flow of the mountain lee vortex. In the case of more easterly prevailing wind, pollutants are transported mainly by the turning flow around the Tar-Tun Mountain and most are carried to the offshore region of Tuo-Yuan and Chung-Li. Due to the resistance of the confluent flow from the lee vortex of the Tar-Tun Mountain and the easterly downslope wind of the Shei Mountain Range, the pollutant concentration doesn't tend to penetrate into the basin under the condition of more easterly synoptic wind. This study has demonstrated the feasibility of the combined application of MM5 model and dispersion model that may be helpful for high-resolution simulation in local regions to understand emergent dispersion processes of nuclear or general air pollutants and are sharable as a tool of real-time operation.

並列關鍵字

Mesoscale Meterorological Model MM5 ； Dynamic Air Dispersion Model ； Atmospheric Planetary Boundary Layer Model