臺灣博碩士論文加值系統

埔里盆地位於台灣中部山區，周圍的地形較複雜，在弱綜觀的大氣環境下，若有高污染事件發生，大氣污染物容易經由海風從西半部傳送至山區，造成埔里盆地的空氣品質變差。山區的局部熱力環流，如上下坡風、山谷風環流，以及邊界層的發展也會影響污染物擴散與累積。因此，本篇利用高解析中尺度氣象模式(WRF)以及地面測站資料來探討(1)埔里盆地熱力環流結構與邊界層發展特性，與(2)山區環流與海陸風的交互作用，以及(3)局部環流和邊界層發展對空氣污染物傳送的影響。

從模擬結果發現：(1)白天太陽加熱地表，因為地表受熱不均，山頂的溫度上升得較快，產生水平的溫度梯度，風向由下坡風轉為上坡風。當盆地周圍發展上坡風時，山頂的風場輻合產生上升氣流，盆地則是風場輻散，在盆地的上方會產生沉降氣流。太陽的加熱與沉降的增溫作用會破壞進地表的逆溫層，大氣呈現混和均勻的狀態。(2)在近中午時，海風進入埔里盆地，與地形交互作用，引發背風波;也會與谷風結合進而增強盆地近地表的風速。(3)在晚上盆地因為輻射冷卻以及下坡風和山風將冷空氣匯集到盆地內，降低近地表的溫度而形成逆溫層，因此上層的綜觀風不易影響到盆地內的大氣運動。

由環保署測站的觀測以及模式(CMAQ)模擬結果發現白天污染物容易在西半部沿海地區生成，經由海風傳送至內陸山區，埔里盆地內的污染物濃度會在中午過後升高;晚上地表受到輻射冷卻，在近地表形成逆溫層，大氣呈現穩定的狀態，因此讓污染物滯留在近地表，無法擴散，但有部分的污染物會被離岸風傳送到西部平原，埔里地區的污染物濃度在午夜過後下降;白天邊界層發展，垂直混合作用增強，降低盆地內污染物的濃度。

Puli basin is located in central mountainous area of Taiwan. The thermally driven circulations such as the upslope/downslope wind and mountain/valley wind generally develop when the synoptic forcing is weak. During high PM2.5 concentration episode, air pollutants mainly produced in the western coastal region can be transported into inland area by sea breeze, and the air quality becomes bad in Puli basin. Air pollutants dispersion is strongly associated with local circulations and atmosphere PBL structure.

In this study, the thermally driven circulations and its subsequent influence on the PBL structure and air pollutant dispersion Puli basin are investigated by using high-resolution mesoscale meteorological model (WRF) and observation data from the Central Weather Bureau (CWB) and air quality monitoring station of Environmental Protection Administration (EPA) in Taiwan.

The upslope winds develop because of the different heating between sloping surface and adjacent plain and leads to the wind divergence and subsidence over the basin in the morning. With the onset of valley wind, the wind speed increase and westerly flow dominate over the basin. Additionally, the atmosphere turns stable to well-mixed condition quickly due to the solar heating and subsiding warming. On the other hand, the radiative cooling and cold air advection produced by downslope and mountain winds form the inversion layer during the night. The surface layer is decoupled from the flow above. Besides, the sea breeze penetrates into mountainous region in the afternoon. The mountain wave is induced by the interaction between the sea breeze and topography. The wind speed increase because of the combination of sea breeze and valley winds.

According to observation data from EPA and CMAQ model results, air pollutants are mostly produced in the western plain and transported by the sea breeze into mountainous region. And the PM2.5 concentration observed at Puli station raise sharply in the afternoon. The inversion layer associated with the radiative cooling and cold air advection forms and causes pollutants accumulate near the surface. With the onset of the mountain wind, the pollutants tend to be transported plainward and the PM2.5 concentration recorded at Puli station decrease. After sunrise, the convective boundary layer develops, the vertical mixing becomes strong and dilutes the concentrations near the surface.

摘要 i
Abstract ii
致謝 iv
Table of Contents v
List of Figures vii
Chapter 1 Introduction 1
Chapter 2 Description of the study episode 5
2.1 Synoptic weather conditions 5
2.2 Overview of PM2.5 concentrations 6
2.3 Summary 8
Chapter 3 Configuration of the numerical weather model 10
3.1 Model description 10
3.2 Shin-Hong (SH) scale aware scheme 11
3.3 Comparison of simulation results 13
3.3.1 Sensitivity to PBL parameterization scheme 13
3.3.2 Comparison with different resolution 15
3.3.3 Comparison with observation data 17
Chapter 4 Characterization of local circulations and PBL structure in Puli basin 19
4.1 Daytime local circulations in Puli basin 19
4.2 The structure of upslope wind and its impact on convective boundary layer 19
4.3 Characteristics of the sea-breeze circulation and its interaction with topography and other local circulation 21
4.4 Nocturnal local circulations in Puli basin 21
4.5 Evolution of PBL structures in the Puli basin 22
Chapter 5 The influence of local circulations on PM2.5 concentrations 23
5.1 Comparison of simulation results 23
5.2 Investigation of air pollutants dispersion 24
Chapter 6 Conclusion and future work 26
References 29
Figure 32

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