台中地區近年來的發展十分迅速，在都市擴建的同時台中地貌也 隨之變化，而導致多樣的汙染問題。因此大氣中的懸浮微粒(Particulate Matter, PM)被視為最受關注的空氣汙染物，然而大多數人還會透過觀 測大氣能見度(Visibility)做為判斷空氣汙染程度的依據。為了解台中 地區長期空氣污染之變化，除了透過地面觀測之能見度與PM2.5 濃度 外，並利用Terra 衛星搭載MODIS (Moderate Resolution Imaging Spectroradiometer)AOD 產品，配合正規化氣膠指數 (Normalized Gradient Aerosol Index, NGAI) 辨識氣膠種類，探討台中地區氣膠的 變化情形。此外亦藉由Landsat 衛星所觀測多波段影像進行土地覆蓋 分類，分析台中地區氣膠變化的原因與土地利用改變之關係，結果顯 示從1993 年至2016 年台中市地表覆蓋物的總面積中，植被減少16%、 人工建物增加11%，顯示台中地區地表覆蓋物的明顯變化，且2006 年開始出現的沙塵顯示氣膠種類變化。觀測結果亦證實不同大氣條件 與土地利用改變對於台中地區的能見度具有相當程度的影響，透過地 面觀測和衛星資料的結合，若能得到更佳解析度的氣膠與氣象場資料， 對於空氣污染的防治也會有所幫助。;Visibility is an indicator usually used by residents to evaluate air quality in urban area. And most people think that the air pollution in PM2.5 concentration getting more serious over Taichung city. Actually, the value of visibility could be affected by not only air pollutants but also meteorological parameters, such as aerosol type, water vapor and planetary boundary layer height. All of the factors will be resulted in the variation of atmospheric extinction which is the most significant to visibility. Therefore, to identify each effect is essential to understand and prevent the worse visibility phenomenon, which is the main objective of this study. As the main component of air pollutants, the relationship with visibility will be examined at first in this study. Both ground-based measurements and satellite observations are collected for the analysis. The measurements of visibility and PM2.5 concentration are collected from ground station. To obtain the temporal and spatial information, the aerosol optical depth (AOD) retrieved from MODIS (Moderate Resolution Imaging Spectroradiometer) over study area is employed and associated with the NGAI (Normalized Gradient Aerosol Index) approach to identify the aerosol type in Ds (Dust), AP (Artificial Pollutants), BB (Biomass Burning). And the land use/land cover changes are also analyzed with Landsat imagery. Although ground based measurements show that air pollution in Taichung area has decreased, but satellite observations do not show that same results. Therefore, long-term data shows high relative humidity (RH) go with low visibility. And NGAI aerosol types appear Ds from 2006 to 2017, but AP remains the main source of aerosol. Compare land use result from 1993 to 2016, showing huge changes in Taichung. Understanding the reason about aerosol type and meteorological parameters change is important.
