落塵數值模式的研究與發展

Abstract

懸浮微粒與落塵是台灣地區本土性的空氣污染問題，但與落塵相關的空氣品質模式之研究卻很少，因此本研究之目的為建立一套與落塵相關之空氣品質模式雛形，並比較不同的垂直解析度設定與粒徑分級對於模擬濃度與沉降量之影響。 本研究比較7種垂直解析度在4種氣象條件下，對於模擬5種粒徑微粒濃度與沉降量的影響。依本研究之結果發現數值模式之垂直解析度對於沉降性微粒(50 μm以上)的濃度與沉降量具敏感性，對於10 μm以下微粒則誤差影響不大。模式第一層離地高度與近地層(100公尺以下)之解析度最具敏感性，第一層離地高度若較高，粒徑大於50 μm之微粒沉降量會明顯低估，濃度則會高估，對於小粒徑微粒的影響則較小。在相同垂直網格數目下，近地層的解析度越高，其誤差較小。 若排放之微粒粒徑分布均勻，10μm以下微粒，以一個粒徑代表，誤差在5 %以下。10~50μm、 50~100μm之微粒，將粒徑各分為2級之誤差皆在10 %以下。顯示要模擬落塵及懸浮微粒，粒徑約分成5個等級即可。

Suspend particulate and dustfall cause great air pollution problem in Taiwan. However, there is few research of air quality model about dustfall. The objective of this study is to build frame of air quality model about dustfall and to compare with the simulation concentration and dustfall amount in different setting of vertical resolution and particle size grading. The results show the vertical resolution is sensitivity to concentration and dustfall amount of deposited particles. The height of first layer and the resolution under 100 m have great influence on simulation result. If the height of first layer is higher, the dustfall amount of particles larger than 50 μm is underestimate obviously and the concentration is overestimate. And if the number of grids in vertical direction is the same, the error is smaller when the resolution under 100 m is higher. If particle size distribution is uniform, the results show that the error between different division of particle size becomes larger as downwind distance gets longer. In this size grade of particles less than 10 μm, the maximum error is less than 5 % by using only one size particle to simulate. In the size grade of particles between 10 to 50 μm and 50 to 100 μm, the maximum error are both within 10% when the size are divided into two grade. It shows a division of particle size into five grade is enough to simulate suspend particulate and dustfall.