| 摘要: | 本研究乃利用多重濾鏡旋轉輻射儀(MFRSR)與太陽輻射儀(CIMELs) 觀測2006年4月至2008年12月鹿林山大氣背景站(2862 m,23.47°N, 120.87°E)氣膠光學特性。並參考Krotkov et al. (2005a)概念，將MFRSR所觀測之直射通量值反演為氣膠光學厚度(AOD500nm)。每年春季期間(3-5月)，AOD500nm、CO與PM10較高，此期間主要受到東南亞生質燃燒污染影響。AOD500nm 與PM10月平均變化趨勢相似，其最高值皆發生在3月份。Ångström exponent月平均值在5-8月相對較低(MFRSR：0.35-0.76, CIMELs：0.73-0.91);冬季12-3月較(MFRSR：1.15-2.14, CIMELs:1.63-2.24)，其相對濕度與垂直水氣量則呈現相反之趨勢。AOD500nm之日變化在中午過後有上升的現象，與PM10濃度變化趨勢類似，而Ångström exponent於午後則明顯驟降，其相對濕度於午後則逐漸攀升。AOD500nm 與 PM10 在相對高壓天氣狀況下有較好相關性，而高度相關發生在冬季(R：0.82-0.86);相關性較差則在夏季與秋季。利用HYSPLIT後推軌跡模式將氣團來源分類，其中來自乾淨海洋之氣膠造成的AOD500nm值最小，來自東南亞則大。Ångström exponent最小值為來自海洋性氣團之氣膠；Ångström exponent最大值則來自高層之氣團。在沙塵與生質燃燒事件中，伴隨氣團之AOD500nm值明顯上升，分別約為海洋性氣團的2.7倍與18倍。由粒徑分布與Ångström exponent值得知沙塵氣膠為粗粒徑的顆粒較多；生質燃燒氣膠則是細粒徑顆粒較多。直射通量與散射通量之比值在污染事件下明顯小於乾淨背景值，而各事件中最大之比值分別為7.42(沙塵事件)、1.41(生質燃燒)與15.32(乾淨背景)，表示在生質燃燒事件中垂直氣柱之氣膠容載量(Aerosol loading)最大，而乾淨環境下氣膠總容載量則最小。 The purpose of this study is to study the vertical optical properties of aerosols observed at Mt. Lulin Atmospheric Background Station (2862 m; 23.47°N, 120.87°E) from April 2006 to December 2008 with simultaneous measurements with a multi-filter rotating shadowband radiometer (MFRSR) and a Cimel’s sunphotometer (CIMELs). Solar direct flux data of MFRSR measurements were retrieved to obtain aerosol optical depth (AOD500nm), based on Krotkov et al. (2005a). The AOD500nm, CO and PM10 were relatively high in spring (March-May), due to the impact of biomass burning from Southeast Asia. The variation of monthly mean AOD500nm and PM10 was similar, with the maximum values occurring in March. Monthly mean Ångström exponent values were lower (MFRSR:0.35-0.76, CIMELs:0.73-0.91) between May and August and higher between December and March (MFRSR:1.15-2.14, CIMELs:1.63-2.24). However, relative humidity and columnar water vapor showed an opposite trend. Besides, the AOD500nm increased in the afternoon, as well as the PM10. The Ångström exponent significantly decreased in the afternoon, but relative humidity gradually increased. AOD500nm and PM10 had a better correlation, relative high-pressure weather conditions under particularly in winter (R:0.82-0.86), while a poor correlation in the summer and autumn. The HYSPLIT trajectory analysis helped classify air mass sources. The minimum AOD500nm was associated with the air mass from the ocean, while maximum value was associated with the air mass from Southeast Asia. The minimum and maximun Ångström exponent were associated with the air mass from the ocean and from the high-level, respectively. The AOD500nm evidently increased during the dust and biomass burning events, and was about 2.7 times and 18 times that in maritime air mass. Based on particle size distribution and Ångström exponent, the dust aerosol had a large mode, while biomass burning aerosol had a fine mode. The ratio of direct flux to diffuse flux in the dust event, biomass burning, and background were 7.42, 1.41, and 15.32, respectively, indicating that the largest vertical column as aerosol loading appeared in the biomass burning event, while the smallest occurred in the clean background air. |
