東沙海域大氣懸浮微粒之來源、傳輸與化學特性研究

Sources, Transport and Chemical Characterization of Atmospheric Aerosols over the Dongsha Island

蕭鈺亭(Yu-Ting Hsiao)

指導教授 ： 林斐然

共同指導教授 ： 蘇志杰(Chih-Chieh Su)

國立臺灣大學/理學院/海洋研究所/碩士(2016年)

https://doi.org/10.6342/NTU201610141

摘要

本研究於2012年在南海北部的東沙島採集279組大氣懸浮微粒標本，這些標本分別以離子層析儀分析Cl-、NO3-、SO42-和NH4+等4個水溶性離子，以感應耦合電漿質譜儀分析Al、Fe、Na、Mg、K、Ca、Sr、Ba、Ti、Mn、Co、Ni、Zn、Mo、Ag、Cd、Sn、Sb、Pb、V、Cr、As、Se和P等24個金屬元素。分析結果顯示東沙海域大氣中各元素濃度變化極大，大致有3-4個數量級的變化。其中Na、Cl-、NO3- 、nss- SO42- 和NH4+濃度最高，平均濃度均大於1 ug/m3，是大氣中的主成分。
大氣中大部分的元素都呈現彼此類似的月變化趨勢，其分布特徵大多以3月、10月和11月的濃度較高，4月至9月濃度較低。其中P的分布比較特別，其最高濃度出現在8月。根據元素相關性及元素富集值的計算，顯示Fe、Al、Ti、Co、Mn、Cr、Ca和Ba主要為地殼來源，Na、Mg、Sr、K和Ca主要為海水來源， V、Ni、Zn、Pb、Cd、As、Sn、Se、Sb及P等主要為污染來源。K、Ca、Sr和Mn等四元素可能有雙重來源或三重來源。主成分分析結果顯示影響東沙海域大氣懸浮微粒組成的因素主要為源自亞洲大陸所帶出的汙染物質及沙塵物質，此影響因子可以解釋東沙海域大氣成分組成變異量的60%以上。研究結果也發現東沙海域大氣懸浮微粒中氯虧損情況相當嚴重，顯示此海域的大氣中有相當多的酸性汙染物(如nss-SO42-和NO3-)介入，導致氯的虧損。東沙海域大氣中的NH4+ /nss- SO42-及NH4+ / NO3-莫耳比值均在2以上，顯示此海域有足夠多的NH4+供應足以形成(NH4)2SO4和NH4 NO3，此可以有效中和大氣中的酸性成分nss- SO42-和NO3-。
東沙海域大氣中的成分組成受東北季風所帶來的亞洲大陸之陸源物質(包括沙塵物質及汙染物質)之影響遠比西南季風所帶來的中南半島及東沙島南方海域之物質之影響來得大。東沙海域之大氣物質有超過一半以上的量是由海水循環上來的海鹽成分，陸源物質僅占三成左右，其中污染源成份之貢獻度約為地殼源成份的2倍。東沙海域大氣中各元素之乾沈降通量以NO3-、nss-SO42-、Ca、K、NH4+、Al和Fe為最大宗，通量值均在100 mg/m2/yr以上，其中屬營養成分的Fe、P和N之乾沉降通量分別為81.9 mg/m2/yr，33.8mg/m2/yr和283 mgN/m2/yr。在N的總通量中，有48%為NO3- 的貢獻，52%為NH4+的貢獻。

關鍵字

南海 ； 東沙 ； 大氣懸浮微粒 ； 微量元素 ； 傳輸 ； 來源鑑別

並列摘要

Two hundred and seventy nine aerosol samples were collected from January to December in 2012 at Dongsha Island in northern South China Sea. The water-soluble ions (Cl-, NO3-, SO42- and NH4+) and metals (Al, Fe, Na, Mg, K, Ca, Sr, Ba, Ti, Mn, Co, Ni, Zn, Mo, Ag, Cd, Sn, Sb, Pb, V, Cr, As, Se and P) were analyzed by ion chromatography (IC) and inductively couple plasma mass spectrometry (ICPMS), respectively. The year-long monitoring results indicate strong variation of elemental concentrations in aerosol samples over the South China Sea. The major chemical components in aerosol samples at the Dongsha Island were composed by Na, Cl-, NO3-, nss-SO42- and NH4+ and their average concentrations were higher than 1 μg/m3. A large proportion of elements concentration in aerosols displayed a similar trend with higher concentration in March, October and November, and lower concentration in April to September. The highest concentration of element P is in August. Correlation coefficient and enrichment factor calculations reveal that the sources of elements can be divided into three categories: (1) Fe, Al, Ti, Co, Mn, Cr, Ca and Ba were mainly derived from crustal sources, (2) Na, Mg, Sr, K and Ca were from seawater sources, and (3) V, Ni, Zn, Pb, Cd, As, Sn, Se, Sb and P were from anthropogenic sources. Among them, K, Ca, Sr and Mn were multisources.
Principal component analysis (PCA) was used to clarify sources and associated processed and it shows the most predominant sources of atmospheric trace species to the South China Sea were mineral dust and anthropogenic materials from mainland China and it occupied more than 60% atmospheric chemical composition. PCA result also indicates the variability of chemical composition of aerosols is greatly influenced by the dust storm during the northeast monsoon season and delivered crustal and anthropogenic materials at Dongsha Island. In contrary, the impact materials derived from Indochina and South China Sea during the southwest monsoon season is relatively small.
The Cl-/Na+ ratios in aerosol samples indicate strong chloride deficient and it suggests the atmosphere over the study area suffered severely acidic ion species pollution. The calculation results of molar ratio between NH4+ and nss-SO42-, NH4+ and NO3- reveal the capability of NH4+ to neutralize the acidic ion species, like nss-SO42- and NO3-, is strong.
In this study, half of the aerosol component was composed by sea salt particles, and land source materials only occupied 30%. Moreover, in land source materials, the contribution from anthropogenic pollution was two times higher than crustal source. The atmospheric dry deposition fluxes of NO3-, nss-SO42-, Ca, K, NH4+, Al and Fe to the Dongsha area were higher than 100 mg/m2/yr which accounts for most of the total atmospheric flux and being the most important input to the Dongsha Island. The estimated fluxes of F, P and N to the Dongsha area were 81.9, 33.8, and 283 mg/m2/yr, respectively. The fraction of total dry deposition fluxes of N were 48% for NO3- and 52% for NH4+.

並列關鍵字

South China Sea ； Dongsha island ； Aerosol ； Trace elements ； transport ； source identification

參考文獻

葉純伶(2011)東沙海域大氣懸浮微粒中水溶性離子之化學特性研究。國立台灣大學海洋研究所碩士論文。40頁。

Arimoto, R., Kim, Y. J., Kim, Y. P., Quinn, P. K., Bates, T. S., Anderson, T. L., Gong, S., Uno, I., Chin, M., Huebert, B.J., Clarke, A. D., Shinozuka , Y., Weber, R.J., Anderson, J.R., Guazzotti, S.A., Sullivan, R.C., Sodeman, D.A., Prather , K.A., and Sokolik, I.N. (2006). Characterization of Asian dust during ACE-Asia.Global and Planetary change, 52(1), 23-56.

Arimoto, R., Ray, B. J., Lewis, N. F., Tomza, U., and Duce, R. A. (1997). Mass‐particle size distributions of atmospheric dust and the dry deposition of dust to the remote ocean. Journal of Geophysical Research: Atmospheres, 102(D13), 15867-15874.

Ballhorn, U., F. Siegert, M. Mason, and Limin, S. (2009). Derivation of burn scar depths and estimation of carbon emissions with LIDAR in Indonesian peatlands, Proceedings of the National Academy of Sciences of the United States of America., 106(50), 21213-21218

Bey, I., Jacob, D. J., Yantosca, R. M., Logan, J. A., Field, B. D., Fiore, A. M., Li, Q., Liu, H. Y., Mickley, L. J., and Schultz, M. G. (2001). Global modeling of tropospheric chemistry with assimilated meteorology: Model description and evaluation. Journal of Geophysical Research: Atmospheres, 106(D19), 23073-23095.