盛行東北季風下北台灣核能電廠附近污染物擴散之數值研究

A Numerical Study of Dispersion of Pollutants near Nuclear Power Plants over Northern Taiwan under Northeast Monsoon

黃清勇(Ching-Yuang Huang) ； 莊銘棟(Ming-Tung Chuang)

《大氣科學》 21卷2期 (1993/09) Pp. 101-124

摘要

本文探討盛行東北季風下近地污染面源於複雜地形的擴散現象，利用一個包含高階亂流閉合的中尺度數值模式來進行個案模擬。模擬結果發現，核一廠的污染物主要是繞行大屯山脈，其中一支分量經由基隆河谷進入台北盆地，核二廠的污染物則大部份經由基隆河谷進入台北盆地。在盛行風較強時，進入台北盆地的核一、二廠污染物，絕大部份會越過林口台地及觀音山巒，進而在三、四小時內污染桃園及新竹等地，其平均近地濃度值則降為約污染源濃度的十分之一。在白天地面加溫作用下，大氣邊界層迅速發展，亂流混合大為增強，此濃度值可再被稀釋約十分之一。但在弱風且近地熱力穩定情況下，台北盆地的最大地面濃度值可達污染源濃度的一半。在穩定情況下，核四廠污染物則對宜蘭地區及台灣東部有較大的影響。當不穩定邊界層出現時，近地污染物因亂流混合而迅速擴散至邊界層頂，再由盛行風作長程輸送，近地氣流受地形的阻擋作用並不明顯。對台灣北部複雜地形而言，福祿數（Froude number）為描述成層穩定氣流的有效物理參數，因此水平平流大致決定了濃度的幾何分佈。但若近地氣流呈現不穩定，則近地亂流擴散作用為決定地面濃度大小的主要因素。

關鍵字

中尺度數值模式 ； 污染物 ； 擴散

並列摘要

This study investigates diffusion processes of surface pollutant sources over complex terrain of northern Taiwan under prevailing northeast monsoon. Numerical simulations were performed by a mesoscale numerical model which employs high-order subgrid turbulence closure. Model simulation results show that pollutants from Station 1 of nuclear power plants tend to split and move around Da-Tun Mountain Range, and then enter Taipei Basin through Kee-Long River, while most of pollutants from Station 2 enter mainly through Kee-Long River. For stronger prevailing winds, pollutants from both stations can be transported over Lin-Kou Tableland and contaminate Tao-Yuan and Hsin-Chu areas by 3-4 hours, with the maximum ground-level pollutant concentration about one-tenth of the original source concentration. With the diurnal surface heating included, the concentration can be further reduced to about one-hundredth. The maximum near-surface concentration over Taipei Basin could retain more than one-half of the source intensity for weaker winds under stable conditions. It was also found that Station 4 has stronger influence on I-Lan area and eastern Taiwan.In the case with diurnal heating, pollutants from near-surface area sources can be promptly transferred upto the boundary-layer top and then are conveyed by the prevailing wind. The case results indicate that Froude number is an effective physical parameter in describing the stably-stratified mountain flow in northern Taiwan and thus horizontal advection largely determines the geometric distributions of the concentration. As the near-surface flow becomes unstable, vertical turbulent diffusion appears to be a dominant factor for concentration intensity.

並列關鍵字

Mesoscale Numerical Model ； Pollutants ； Diffusion