中壢地區光達消光散射比之長期分析與污染物關聯性研究

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Title:	中壢地區光達消光散射比之長期分析與污染物關聯性研究
Authors:	李慶偉;Lei,Heng-wai
Contributors:	大氣物理研究所
Keywords:	光達;消光散射比;Lidar;Backscatter to scatter ratio
Date:	2014-08-29
Issue Date:	2014-10-15 14:31:13 (UTC+8)
Publisher:	國立中央大學
Abstract:	大氣氣膠種類對於污染物來源追蹤、衛星觀測反演假設、及輻射驅動力計算等皆有顯著的影響，而東亞為全球氣膠種類最複雜之區域，如何有效判別氣膠種類，為一個具有挑戰性的課題。過去研究指出，光達消光散射比(Lidar ratio, Sp)對應其他氣膠光學參數，能有效應用於區分氣膠種類。因此，本研究著重分析微脈衝光達長期消光散射比等資料，輔以氣膠垂直剖面分類及氣流後推軌跡資訊，解析中壢地區光達消光散射比與氣膠來源類型之關聯性。分析環保署中大站2005-2012年長期資料結果顯示，3月氣膠光學厚度最高約0.8，為平均值(0.4)的兩倍，說明春季受境外傳送影響顯著。結合氣膠消光係數垂直剖面與氣膠傳送特徵，歸納出兩種氣膠垂直分布結構：Type 1 (單層傳送)與Type 2 (雙層氣膠)，其中Type 1常出現秋季(10，11月)，而Type 2主要出現於春季(3，4月)。Type 1中，根據氣流區分不同來源區域對應之Sp，發現亞洲大陸(Asia continental, AC)、太平洋(Pacific ocean, PO)、東南亞地區(Southeast Asia, SA)分別為3917sr、3012sr、3818sr，因Sp值越低代表氣膠光學散射特性越明顯，推估AC有微量沙塵特性，PO則與海洋氣膠類型一致。進一步結合環保署沙塵暴監測網資料，分析Type 2於不同高度下之氣流軌跡，將沙塵暴與生質燃燒事件進一步篩選，結果發現沙塵期間Sp平均值為4016sr，生質燃燒期間Sp頻率分布呈現鞍形分布特性，第一峰值30-50sr，第二峰值範圍60sr至80sr，前者與都市污染有關，後者呈現生質燃燒氣膠特性。本研究透過簡化分類氣膠垂直剖面，並結合後推氣流軌跡分析，以Sp做為鑑別氣膠來源種類的指標，歸納出傳送至中壢地區之氣膠約略可分為四種類型：都市、沙塵、生質燃燒與海洋性氣膠，其Sp分別為4218、346、6912與3012sr，此結果有助於未來污染物來源監測之應用。 ;ABSTRACT Aerosol types play an important role for air pollutant tracking, satellite retrieval, and atmospheric radiation calculation. In addition, East Asia is the most complex region of aerosol type in the world, and aerosols type classification could be challenge for this region. Pervious studies proven that the extinction to backscatter ratio (lidar ratio, Sp) can be applied to distinguish aerosols types effectively. Therefore, this study focus on studying the relationship between aerosol types and aerosol optical properies. We analyzed long-term data of Sp and other optical properties. Information of the aerosol vertical uding distribution and air mass trajectories was used to clarify our founding. Eight years (2005-2012) of EPA-NCU Micro-PulseLidar observationswere applied in this study. Seasonal variation of aerosol optical depth (AOD) shows highest AOD (~0.8) in Mar, about two times higher than average value of 0.4. The high AOD in spring is attributed to long-range transport of biomass-burning aerosols from Indochina According to aerosol profile classification, extinction profiles were classified into two types: Type 1 (near-surface aerosol transport) and Type 2 (double layer aerosol transport). Fall season (Oct-Nov) is the prevailing season for the Type 1, whereas Type 2 mainly happened in spring (Mar-Apr). In type 1, air masses were travelled from 3 sectors: Asia continental (AC), Pacific Ocean (PO), and Southeast Asia (SA). The mean Sp values for the three sectors are 3917sr for AC, 3012sr for PO, and 3818sr for SA. According the meaning of Sp, a low Spimplies a stronger scattering characteristic. The Sp results suggest aerosol from AC sector contain dust particle, and aerosols from PO are most likely sea-salt. We further combine the EPA dust event database and backward trajectory analysis for Type 2. Results show that Sp is 4114sr for dust storm events. The histogram of Sp for biomass burning events in Type 2 shows two peaks pattern. The first peak occurred within range of 30-50sr corresponding to urban pollutant, whilesecond peak occurred within range of 60-80sr in relation to biomass burning. Finally, our study summarized the Sp values for four major aerosol types over NCU：Urban (4218sr), Dust (346sr), Biomass burning (6912sr), Oceanic (3012sr). The relationship between Sp and aerosol types based on our study can be applied to air pollutant monitoring.
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