Long-term wintertime cloud water chemistry observed at Mt. Bamboo in Taiwan: Overall characteristics and impact of biomass burning

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Title:	Long-term wintertime cloud water chemistry observed at Mt. Bamboo in Taiwan: Overall characteristics and impact of biomass burning
Authors:	裴秋水;Thuy, Bui Thu
Contributors:	大氣科學學系
Date:	2017-08-23
Issue Date:	2017-10-27 12:27:42 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究探究北台灣竹子山 (25.18oN, 121.53oE; 1,100 m MSL) 1996-2016年於東北季風季受亞洲大陸長程傳輸影響時候之雲霧水化學。雲霧水為每小時採樣，每個樣本會分析其pH值及無機水溶性離子。在觀測之20年期間，共採得180個雲事件，5480個雲霧水樣本。雲事件及混合事件(同時有雲霧及降雨)的pH值中位數分別為4.0及4.4。雲霧水離子之主要成份為海鹽離子(Na+, Cl-) 及非海鹽硫酸根 (nss-SO42-)，可能與氣團來自於亞洲大陸有關。Nss-SO42- 隨時間有下降的趨勢，可能與中國有效控制SO2之排放有關。應用後推軌跡聚類分析探討源與受體之關係，顯示雖然中國北部之排放量比中國中部及中南半島高，但在中國北部地區之雲霧中離子濃度卻比中國東部及中南半島分類低，因此推測傳輸路徑比排放源的排放量更能影響測站之雲霧水化學。整合後推軌跡、遙測及氣象資料協助探討兩個高污染事件。於2002/03/22-24的個案中，顯示兩個不同污染物來源雲團之垂直混合(較低層包括亞洲大陸人為污染物及沙塵；高層則包含生質燃燒污染物)。而於2016/01/18-23之個案中，發現亞洲大陸之氣團帶來高污染的雲團，及後因雨水稀釋，後期之雲團就比較乾淨。本研究還發現來自中南半島生質燃燒之氣膠，於採樣期間經高壓系統下大氣沉降，對測站之雲霧水離子濃度造成影響。然而在1996-2016年，只發現有10宗個案，數量很少。此外，可定義西太平洋相對乾淨之氣團影響雲霧水中離子濃度為背景值。 ;This study investigated long-term chemistry of cloud water at Mt. Bamboo (25.18oN, 121.53oE; 1,100 m MSL) in northern Taiwan under primary influence of Asian continental outflows during northeast monsoon seasons, in 1996-2016. Cloud water was collected on an hourly basis. Samples were measured with pH and inorganic soluble ions were analyzed. In total, 180 cloud events were observed with 5,480 samples collected. Long-term median pH values are 4.0 and 4.4 for cloud samples and mixed (cloud and rain at the same time) samples, respectively. Major contributors in cloud water were sea-salt components (Na+, Cl-) and nss (non sea-salt)-SO42- which might be associated with Asian continental outflow. Nss-SO42- concentration showed a significant decreasing trend over time, which was probably attributed to SO2 emission reduction in China. Relationship between source and receptor was studied by using trajectory cluster analysis. Although northern China is a greater source region comparing to central China and Indochina, ion cloud loading of air mass coming from northern China cluster region show lower values than those from central China and Indochina cluster regions, suggesting that transport pathway’s role may override source emission’s. Two cases with extremely cloud events observed were studied using a combination of backward trajectory, remote sensing tools and meteorology data. The case of 2002/03/22-24 evidenced a vertical mixing of 2 polluted cloud layers (lower layer includes Asian anthropogenic species and dust; upper layer includes biomass burning species). The case of 2016/01/18-23 depicted a polluted cloud period corresponding to a strong influence from Asian continental outflow, followed by a clean cloud period due to the rain-out effect. It was also found that biomass burning aerosol from Indochina can impact the site during sampling periods due to the air mass subsidence via pressure high. However, impact was rarely observed (10 cases over 1996-2016).
Appears in Collections:	[Department of Atmospheric Sciences and Graduate Institute of Atmospheric Physics ] Department of Earth Sciences

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