| 摘要: | 大氣氣膠光學效應會影響地球接收和反射太陽輻射，因此，觀測大氣氣膠光學特性是評估全球暖化的重要項目。台灣中部鹿林山(2,862 m a.s.l.)大氣背景站適合觀測東亞背景大氣氣膠的光學特性，雖然鹿林山屬於高山背景測站，但是仍會受到亞洲大陸污染傳送與春季中南半島生質燃燒的長程傳輸污染影響。本文分析2008年10月至2010年4月鹿林山受到不同氣團的氣膠光學特性，研究氣膠粒徑分布與氣膠化學成分變化對氣膠光學特性的影響，以及利用模式推估不同氣團乾氣膠直接輻射效應，並且與實際大氣氣膠直接輻射效應進行比較。 鹿林山接收到的氣團主要為源區生質燃燒(BB)、源區非生質燃燒(SNBB)、自由大氣(FT)、人為污染(Anthropogenic)等四種類型。源區生質燃燒(BB)類型的氣團經過長程傳輸帶來高濃度的硫酸鹽氣膠與碳成分氣膠，PM10氣膠散光係數和吸光係數分別為127.2 Mm-1與24.6 Mm-1；源區非生質燃燒(SNBB)類型的氣團是長程傳輸的背景濃度，氣膠散光係數和吸光係數分別為23.2 Mm-1與3.1 Mm-1；自由大氣(FT)類型的氣團是代表東亞背景大氣的特性，氣膠散光係數和吸光係數分別為25.0 Mm-1與4.2 Mm-1；人為污染(Anthropogenic)類型的氣團包含中國東南方污染傳送與白天谷風帶來的本地污染，白天谷風造成PM10氣膠散光係數和氣膠吸光係數24小時平均影響量分別為15.1 Mm-1與1.6 Mm-1。源區生質燃燒、源區非生質燃燒、自由大氣、人為污染等四種類型氣團的氣膠直接輻射效應分別為-0.25、-0.22、-0.17、-0.60 W m-2，在生質燃燒期間氣膠單次散射反照率的低值與氣膠光學厚度的高值，會減低大氣氣膠對地球接收太陽直接輻射的冷卻效應。此外，考慮到氣膠化學成分會影響氣膠含水量，造成實際大氣氣膠散光效應會增加30.7%、2.5%、63.8%、37.7%，導致估算氣膠直接輻射效應需要修正。 The optical effects of atmospheric aerosol would influence solar radiation received and reflected by earth, therefore, the assessment of atmospheric aerosol optical properties on global warming is an important project. Lulin Atmosphere Background Station (LABS) at Mt. Lulin (2,862 m a.s.l.) in central Taiwan aims to observe the East Asian background atmospheric aerosol properties. Although Mt. Lulin is an elevated background station, it would still be affected by the Asian continental pollution and Indochina biomass burning through long-range transport. The purpose of this study is to analyze the impact of aerosol size distribution and aerosol chemical composition on the effects of changes in aerosol optical properties and use different models to estimate aerosol direct radiative effects for different air masses arriving at Mt. Lulin from October 2008 to April 2010. The air masses were classified into four types as air masses from source area of biomass burning (BB), source area of biomass burning during non-BB period (SNBB), free atmosphere (FT), and Anthropogenic sources (Anthropogenic). The BB type of air masses bring high concentrations of sulfate aerosol and carbon content of aerosol through the long-range transport. PM10 aerosol scattering coefficient and absorption coefficient could reach 127.2 Mm-1 and 24.6 Mm-1 respectively. For SNBB, aerosol scattering coefficient and absorption coefficient were 23.2 Mm-1 and 3.1 Mm-1 respectively. The FT type represented the East Asian clean background atmosphere properties. For FT, aerosol scattering coefficient and absorption coefficient were 25.0 Mm-1 and 4.2 Mm-1, respectively. For Anthropogenic type, air masses lower atmosphere of Asian continent and valley-breeze driven local pollution caused 15.1 Mm-1 and 1.6 Mm-1 for aerosol scattering coefficient and absorption coefficient, respectively. The direct radiative effects for BB, SNBB, FT, and Anthropogenic were -0.25, -0.22, -0.17, -0.60 W m-2, respectively. Lower single scattering albedo and higher aerosol optical depth would reduce the cooling effect of direct solar radiation during the biomass burning period. In addition, taking into account the aerosol water content affected by aerosol chemical compositions, the resulting aerosol scattering effect would increase by 30.7%, 2.5%, 63.8%, 37.7% for BB, SNBB, FT, and Anthropogenic, respectively. |
