Characterization of wintertime precipitation chemistry at sites in the northern Taiwan

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Title:	Characterization of wintertime precipitation chemistry at sites in the northern Taiwan
Authors:	林杜伊;Linh, Do Thi Thuy
Contributors:	大氣科學學系
Keywords:	降水化學;長程傳輸;臺灣北部;沙塵傳送;Precipitation chemistry;long-range transport;northern Taiwan;dust transportation
Date:	2019-03-21
Issue Date:	2019-04-02 14:08:30 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究中，我們分析了北臺灣三個地點：臺北、鞍部及彭佳嶼的冬季長期資料(2008-2017年)。主要研究目的是利用Mann-Kendall檢定法及Sen斜率推估法，以雨水採樣品中無機成分之濃度特徵，探討這些採樣點的降水化學特性、時空分布上的長期趨勢與降雨類型對雨水採樣的影響。在這段分析期間，臺北、鞍部及彭佳嶼的平均雨水酸鹼值分別為4.91、4.73和4.70，而雨水樣品的酸鹼值主要與NO3-、nss-SO42-、NH4+、K+、Mg2+和Ca2+等有密切相關。長期趨勢發現總體酸鹼值有上升趨勢，此現象可歸因於Ca2+增加，而鞍部、彭佳嶼兩處nss-SO42-之濃度下降也可能使雨水酸鹼值下降，但臺北則因都市排放而有不同變化；由於採樣位置差異及降水性不同，使得彭佳嶼的海鹽離子、NO3-和nss-SO42-均高於另外兩個採樣點。此外，人為排放的變化與氣團在區域傳輸的狀態也會影響分析結果。而不同的降水類型議會影響化學分析結果，由東北季風所帶來的降水，其樣品中的離子濃度會較鋒面系統所引起的降水來得大，但數值差異不大，因此可推測影響降雨化學的主因來自於人為活動。最後，透過Ca2+的分析結果，可將事件分為兩類：96%為長程傳輸與人為排放混合事件，以及4%的單純沙塵傳送事件。霾害事件則在當中扮演重要角色，因其對於人為排放的垂直混合具有負面影響。 ;In this study, the long-term (2008-2017) winter precipitation chemistry at three sites in northern Taiwan, including Pengjia islet, Anbu, and Taipei, was analyzed. The major aims of this study are: report the characterization of inorganic component concentrations in rainwater, discuss the spatial distribution, and evaluate the long-term trends of the precipitation chemistry and the effect of weather type on rainfall composition at these sampling locations. The Mann-Kendall test and Sen’s estimation of the slope were employed to detect the long-term trends. Over the entire period, a mean pH of 4.91, 4.73, and 4.70 was found at Taipei, Anbu, and Pengjia islet, respectively. pH of the rainwater samples was strongly related to the concentration of NO3-, non-sea-salt (nss-) SO42- and acid-neutralizing compounds such as NH4+, K+, Mg2+, and Ca2+. Sea salt ions, NO3-, and nss-SO42- were all higher at Pengjia islet than Anbu and Taipei. This can, in part, be explained by the difference in sampling location as well as characteristics of the precipitation. Long-term trends in the precipitation chemistry indicated a significant increase in pH at all sites and could be attributed to a significant increase in Ca2+. At Pengjia islet and Anbu, the decrease in nss-SO42- concentration may have also contributed to the increase in pH, while Taipei showed a different pattern likely due to the impact of local emission. In addition, changes in anthropogenic emissions and the regional transport pattern of air masses may have contributed as well, impacting the precipitation chemistry at all three sites. Rainfall type also contributed to the difference in precipitation chemistry. Precipitation caused by the North-east monsoon (NE) showed a greater ion concentration than precipitation caused by frontal systems (FS) because of the lower precipitation amount in the former. Even so, the contribution fraction of major ions was similar between precipitation stemming from these two types of weather systems, suggesting similar anthropogenic emission sources during both. Effects on precipitation chemistry from the long-range transport of dust at Anbu was assessed through examining high Ca2+ events analysis. Two types of events are classified: 96% of events are associated with the mixing of dust and anthropogenic emission during transport and 4% of events may be considered as pure dust transportation. A haze event can be considered as a factor contributing to the difference between the two event types because of its negative effect on vertical mixing of anthropogenic emissions.
Appears in Collections:	[Department of Atmospheric Sciences and Graduate Institute of Atmospheric Physics ] Department of Earth Sciences

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